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Convergent Evolution

“For just the same reason, it is vanishingly improbable that exactly the same evolutionary pathway should ever be traveled twice. And it would seem similarly improbable, for the same statistical reasons that two lines of evolution should converge on exactly the same endpoint from different starting points”--Richard Dawkins (TBW:94).

Initially Posted: July 10, 2005

Last Updated: October 13, 2007

Convergent Evolution Defined:

“When similar structures that are not inherited from a common ancestor evolve in unrelated animals, we call it convergence, or convergent evolution.” This phenomenon is also known as parallel evolution"(IPZ:339).

 

 

The Design Significance of Convergence:

1. “Repeatable Evolution or Repeated Creation?” , By Fazale R. Rana, Ph.D.

 

2. "Convergence: Evidence for a Single Creator", By Fazale R. Rana, Ph.D.

 


Convergent Animal Behaviors:

Echolocation in Birds and Bats:

“This is nowhere better illustrated than in the case we used for our basic illustration of good design itself-echolocation. Most of what we know about echolocation comes from bats (and human instruments), but it also occurs in a number of unrelated groups of animals. At least two separate groups of birds do it, and it has been carried to a very high level of sophistication by dolphins and whales. Moreover, it was almost certainly ‘discovered’ independently by at least two different groups of bats. The birds that do it are the oil birds of South America, and the cave swiftlets of the Far East, the ones whose nests are used for birds’ nest soup. Both types of bird nest deep in caves where little or no light penetrates, and both navigate through the blackness using echoes from their own vocal clicks. In both cases the sounds are audible to humans, not ultrasonic like the more specialized bat clicks. Indeed, neither bird species seems to have developed echolocation to such a pitch of sophistication as bats have. Their clicks are not FM, nor do they appear suitable for Doppler-shift speed metering. Probably, like the fruit bat Rousettus, they just time the silent interval between each click and its echo.

In this case we can be absolutely certain that the two bird species have invented echolocation independently of bats, and independently of each other" (TBW:95).

Echolocation in Dolphins:

“Dolphins emit rapid trains of high-pitched clicks, some audible to us, some ultrasonic. It is probable that the ‘melon,’ the bulging dome on the front of a dolphin’s head, looking-pleasing coincidence-like the weirdly bulging radar dome of a Nimrod ‘advance-warning’ surveillance aircraft, has something to do with beaming the sonar signals forwards, but its exact workings are not understood. As in the case of bats, there is a relatively slow ‘cruising rate’ of clicking, rising to a high-speed (400 clicks per second) buzz when the animal is closing in on prey. Even the ‘slow’ cruising rate is pretty fast. The river dolphins that live in muddy water are probably the most skilled echolocators, but some open-sea dolphins have been shown in tests to be pretty good too. An Atlantic bottlenose dolphin can discriminate circles, squares and triangles (all of the same standardized area), using only its sonar. It can tell which of two targets is the nearer, when the difference is only 11/4 inches at an overall distance of about 7 yards. It can detect a steel sphere half the size of a golf ball, at a range of 70 yards. This performance is not quite as good as human vision in a good light, but probably better than human vision in moonlight” (TBW:96).

“At least two groups of bats then, two groups of birds, toothed whales, and probably several other kinds of mammals to a smaller extent, have all independently converged on the technology of sonar, at some time during the last hundred million years. We have no way of knowing whether any other animals not extinct—pterodactyls perhaps?-also evolved the technology independently” (TBW:97).

Electrolocation in South American and the African Fish:

“No insects and no fish have so far been found to use sonar, but two quite different groups of fish, one in South America and one in Africa, have developed a somewhat similar navigation system, which appears to be just about as sophisticated and which can be seen as a related, but different solution to the same problem. These are so-called weakly electric fish. The word ‘weakly’ is to differentiate them from strongly electric fish, which use electric fields, not to navigate, but to stun their prey. The stunning technique, incidentally, has also been independently invented by several unrelated groups of fish, for example electric ‘eels’(which are not true eels but whose shape is convergent on true eels) and electric rays.

The South American and the African weakly electric fish are quite unrelated to each other, but both live in the same kinds of waters in their respective continents, waters that are too muddy for vision to be effective. The physical principle that they exploit-electric fields in water-is even more alien to our consciousness than that of bats and dolphins. We at least have a subjective idea of what an echo is, but we have almost no subjective idea of what it might be like to perceive an electric field. We didn’t even know of the existence of electricity until a couple of centuries ago. We cannot as subjective human beings empathize with electric fish, but we can, as physicists, understand them.

It is easy to see on the dinner plate that the muscles down each side of any fish are arranged as a row of segments, a battery of muscle units. In most fish they contract successively to throw the body into sinuous waves, which propel it forwards. In electric fish, both strongly and weakly electric ones, they have a battery in the electric sense. Each segment (‘cell’) of the battery generates a voltage. These voltages are connected up in series along the length of the fish so that, in a strongly electric fish such as an electric eel, the whole battery generates as much as 1 amp at 650 volts. An electric eel is powerful enough to knock a man out. Weakly electric fish don’t need high voltages or currents for their purposes, which are purely information-gathering ones.

The principle of electrolocation, as it has been called, is fairly well understood at the level of physics though not, of course, at the level of what it feels like to be an electric fish. The following account applies equally to African and South American weakly electric fish: the convergence is that thorough. Current flows from the front half of the fish, out into the water in lines that curve back and return to the tail end of the fish. There are not really discrete ‘lines’ but a continuous ‘field’, an invisible cocoon of electricity surrounding the fish’s body. However, for human visualization it is easiest to think in terms of a family of curved lines leaving the fish through a series of portholes spaced along the front half of the body, all curving round in the water and diving into the fish again at the tip of its tail. The fish has what amounts to a tiny voltmeter monitoring the voltage at each ‘porthole.’ If the fish is suspended in open water with no obstacles around, the lines are smooth curves. The tiny voltmeters at each porthole all register the voltage as ‘normal’ for their porthole. But if some obstacle appears in the vicinity, say a rock or an item of food, the lines of current that happen to hit the obstacle will be changed. This will change the voltage at any porthole whose current line is affected, and the appropriate voltmeter will register the fact. So in theory a computer, by comparing the pattern of voltages registered by the voltmeters at all the portholes, could calculate the pattern of obstacles around the fish. This is apparently what the fish brain does. Once again, this doesn’t have to mean that the fish are clever mathematicians. They have an apparatus that solves the necessary equations, just as our brains unconsciously solve equations every time we catch a ball.

It is very important that the fish’s own body is kept absolutely rigid. The computer in the head couldn’t cope with the extra distortions that would be introduced if the fish’s body were bending and twisting like an ordinary fish. Electric fish have, at least twice independently, hit upon this ingenious method of navigation, but they have had to pay a price: they have had to give up the normal, highly efficient, fish method of swimming, throwing the whole body into serpentine waves. They have solved the problem by keeping the body stiff as poker, but they have a single long fin all the way along the length of the body. Then instead of the whole body being thrown into waves, just the long fin is. The fish’s progress through the water is rather slow, but it does move, and apparently the sacrifice of fast movement is worth it: the gains in navigation seem to outweigh the losses in speed of swimming. Fascinatingly, the South American electric fish have hit upon almost exactly the same solution as the African ones, but not quite. The difference is revealing. Both groups have developed a single long fin that runs the whole length of the body, but in the African fish it runs along the back whereas in South American fish it runs along the belly. This kind of difference in detail is very characteristic of convergent evolution, as we have seen. It is characteristic of convergent designs by human engineers too, of course” (bold emphasis is mine) (TBW:97-99).

Convergent Behavior in Finches:

"The other seven species divide into three groups: those who live in the trees on fruits and insects; strict vegetarians of the trees; and tree-dwellers who embody 'convergent evolution'-they sing, act, and feed so much like warblers that they were at first taken to be warblers" (AG:30).

Convergence Between Moles and Other Burrowing Animals:

“…the profound and extensive convergence between the moles and the many other burrowing animals (Nevo 1999)….” (GD:336).

  • “…the close similarity in the societal structure of sperm whales and elephants (Weilgart et al. 1996)…” (GD:336).

 

Evidence from opsin genes rejects nocturnality in ancestral primates

( color vision | diurnal | nocturnal | primate life style | prosimian )

Ying Tan *, Anne D. Yoder , Nayuta Yamashita , and Wen-Hsiung Li *¶
*Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637; Department of Biology, University of Massachusetts, 100 Morrissey Boulevard, Boston, MA 02125; Department of Ecology and Evolutionary Biology, Yale University, P.O. Box 208105, 21 Sachem Street, New Haven, CT 06520; and Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089

Contributed by Wen-Hsiung Li, August 14, 2005

"It is firmly believed that ancestral primates were nocturnal, with nocturnality having been maintained in most prosimian lineages. Under this traditional view, the opsin genes in all nocturnal prosimians should have undergone similar degrees of functional relaxation and accumulated similar extents of deleterious mutations. This expectation is rejected by the short-wavelength (S) opsin gene sequences from 14 representative prosimians. We found severe defects of the S opsin gene only in lorisiforms, but no defect in five nocturnal and two diurnal lemur species and only minor defects in two tarsiers and two nocturnal lemurs. Further, the nonsynonymous-to-synonymous rate ratio of the S opsin gene is highest in the lorisiforms and varies among the other prosimian branches, indicating different time periods of functional relaxation among lineages. These observations suggest that the ancestral primates were diurnal or cathemeral and that nocturnality has evolved several times in the prosimians, first in the lorisiforms but much later in other lineages. This view is further supported by the distribution pattern of the middle-wavelength (M) and long-wavelength (L) opsin genes among prosimians.

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Author contributions: Y.T. and W.-H.L. designed research; Y.T. performed research; A.D.Y. and N.Y. contributed new reagents/analytic tools; Y.T., A.D.Y., and W.-H.L. analyzed data; and Y.T., A.D.Y., N.Y., and W.-H.L. wrote the paper.

¶To whom correspondence should be addressed.

Wen-Hsiung Li, E-mail: whli@uchicago.edu"

 

 


Convergent Animal Structures:

  • “…the huge stabbing canines of the saber-toothed cats and the marsupial thylacosmilids (Churcher 1985)…” (GD:336).
  • “As is well known, the vertebrae eye is strongly convergent on that of the squid and octopus, advanced representatives of the cephalopod mollusks. This is a textbook example of evolutionary convergence, and although there are differences the overall similarity is impressive” (GD:337).
  • “It is much less often remarked that the camera-eye has evolved independently several other times, notably in the alciopid polychaetes (Hermans and Eakin 1974), as well as in at least three groups of snails: heteropods, littoriniids (Hamilton et al. 1983), and strombids (Gillary and Gillary 1979)” (GD:337).
  • "First evidence of a venom delivery apparatus in extinct mammals

    Nature 435, 1091-1093 (23 June 2005) | doi: 10.1038/nature03646

    Richard C. Fox and Craig S. Scott

    Numerous non-mammalian vertebrates have evolved lethal venoms to aid either in securing prey or as protection from predators, but modern mammals that use venoms in these ways are rare, including only the duck-billed platypus (Ornithorhynchus), the Caribbean Solenodon, and a few shrews (Soricidae) (Order Insectivora)1. Here we report evidence of a venom delivery apparatus in extinct mammals, documented by well-preserved specimens recovered from late Palaeocene rocks in Alberta, Canada2, 3. Although classified within Eutheria, these mammals are phylogenetically remote from modern Insectivora4 and have evolved specialized teeth as salivary venom delivery systems (VDSs) that differ markedly from one another and from those of Solenodon and shrews. Our discoveries therefore show that mammals have been much more flexible in the evolution of VDSs than previously believed, contradicting currently held notions that modern insectivorans are representative of the supposedly limited role of salivary venoms in mammalian history. Evidently, small predatory eutherians have paralleled colubroid snakes5 in evolving salivary venoms and their delivery systems several times independently.

    1. Laboratory for Vertebrate Paleontology, Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada

    Correspondence to: Richard C. Fox Correspondence and requests for materials should be addressed to R.C.F. (Email: richard.fox@ualberta.ca).

    Received 14 February 2005; Accepted 15 April 2005"

 

Edited by F. Clark Howell, University of California, Berkeley, CA, and approved October 7, 2005 (received for review June 12, 2005)

"The "false thumb" of pandas is a carpal bone, the radial sesamoid, which has been enlarged and functions as an opposable thumb. If the giant panda (Ailuropoda melanoleuca) and the red panda (Ailurus fulgens) are not closely related, their sharing of this adaptation implies a remarkable convergence. The discovery of previously unknown postcranial remains of a Miocene red panda relative, Simocyon batalleri, from the Spanish site of Batallones-1 (Madrid), now shows that this animal had a false thumb. The radial sesamoid of S. batalleri shows similarities with that of the red panda, which supports a sister-group relationship and indicates independent evolution in both pandas. The fossils from Batallones-1 reveal S. batalleri as a puma-sized, semiarboreal carnivore with a moderately hypercarnivore diet. These data suggest that the false thumbs of S. batalleri and Ailurus fulgens were probably inherited from a primitive member of the red panda family (Ailuridae), which lacked the red panda's specializations for herbivory but shared its arboreal adaptations. Thus, it seems that, whereas the false thumb of the giant panda probably evolved for manipulating bamboo, the false thumbs of the red panda and of S. batalleri more likely evolved as an aid for arboreal locomotion, with the red panda secondarily developing its ability for item manipulation and thus producing one of the most dramatic cases of convergence among vertebrates."

 

" By Paul Rincon, BBC News Online science staff

Tuna and mako sharks have evolved very similar swimming anatomy despite being separated by millions of years of evolution, the journal Nature reports.

The findings provide an exceptional example of "convergent evolution", US and German researchers claim.

The two fish types diverged on separated evolutionary paths about 400 million years ago, yet their bodies have come together on a similar design.

This could be the result of exploiting similar ecological niches, experts say.


"It's a fairly major change in anatomy to have that happen. That is the thing that makes it remarkable to us, that this arose independently in the two fish," Professor Robert Shadwick, of Scripps Institution of Oceanography, US, told BBC News Online.

Most fish move their tails by sending a wave of contraction along the length of the body. But this contraction must be limited in its power because each movement of the tail involves bending much of the fish's body.

Red and white

Tuna can drive a powerful tail movement by making forceful muscle contractions in the centre of their bodies. This is facilitated by a unique anatomical arrangement under the skin.

The complex evolutionary changes that gave rise to this anatomy were thought only to have occurred in tuna.

But when researchers from Scripps studied the swimming of mako sharks - related to the famous great white shark - they made some important findings.


The scientists placed mako sharks on a kind of aquatic treadmill - a tube that circulates water from the tail of the fish to the head - so that they swam in place.

They measured the shortening, or contraction, of two different types of muscle in the sharks: red and white.

Fish use white muscle for short bursts of power, but it rapidly fatigues. Active swimming requires red muscle, which is fatigue-resistant.

In tunas and makos, muscle mass is concentrated at the centre of the body and linked to the tail via long tendons. In other fish, the muscle is arranged in blocks along the body attached to the vertebral column, which corresponds with their style of swimming.

When mako sharks swim actively, shortening of red muscle occurs in step with bending of the backbone nearer the tail. Therefore, red muscle at the centre of the body causes movement toward the end of the tail, a pattern of movement seen in tuna.

Supreme predators

Professor Ian Johnston, of St Andrews University, UK, said he could think of more striking examples of convergent evolution.

"If you take biological antifreezes, completely unrelated taxonomic and geographical groups have come up with the same molecule, in some cases deriving it from a different starter molecule.


"[Mako sharks and tuna] inhabit tropical, semi-tropical oceans which are effectively like deserts in terms of food supply. So they have to migrate over long distances, swim very efficiently; they're large and reach high speeds.

"They're supreme predators of the ocean, so they've both evolved from different starting points to that top predator, pelagic niche."

Dr Adam Summers, of the University of California, Irvine, US, speculated that understanding the mechanisms behind the locomotion of tuna and mako sharks could lead to high-speed autonomous underwater vehicles.

"The data from these two high-speed swimmers seem clearly to endorse a solution that puts as much emphasis on the placement of actuators as on the overall shape of the vehicle," he said."

 

 

Convergent Defense Mechanisms:

1. Convergent evolution of chemical defense in poison frogs and arthropod prey between Madagascar and the Neotropics

" Valerie C. Clark *, , , Christopher J. Raxworthy , Valérie Rakotomalala , Petra Sierwald ¶ and Brian L. Fisher ||

*Department of Chemistry, Columbia University, New York, NY 10027; Department of Herpetology, American Museum of Natural History, New York, NY 10024; Department of Animal Biology, Université d'Antananarivo, Antananarivo, 1001, Madagascar; ¶Department of Zoology, Field Museum of Natural History, Chicago, IL 60605; and ||Department of Entomology, California Academy of Sciences, San Francisco, CA 94103

Edited by Jerrold Meinwald, Cornell University, Ithaca, NY, and approved July 1, 2005 (received for review April 27, 2005)

With few exceptions, aposematically colored poison frogs sequester defensive alkaloids, unchanged, from dietary arthropods. In the Neotropics, myrmicine and formicine ants and the siphonotid millipede Rhinotus purpureus are dietary sources for alkaloids in dendrobatid poison frogs, yet the arthropod sources for Mantella poison frogs in Madagascar remained unknown. We report GC-MS analyses of extracts of arthropods and microsympatric Malagasy poison frogs (Mantella) collected from Ranomafana, Madagascar. Arthropod sources for 11 "poison frog" alkaloids were discovered, 7 of which were also detected in microsympatric Mantella. These arthropod sources include three endemic Malagasy ants, Tetramorium electrum, Anochetus grandidieri, and Paratrechina amblyops (subfamilies Myrmicinae, Ponerinae, and Formicinae, respectively), and the pantropical tramp millipede R. purpureus. Two of these ant species, A. grandidieri and T. electrum, were also found in Mantella stomachs, and ants represented the dominant prey type (67.3% of 609 identified stomach arthropods). To our knowledge, detection of 5,8-disubstituted (ds) indolizidine iso-217B in T. electrum represents the first izidine having a branch point in its carbon skeleton to be identified from ants, and detection of 3,5-ds pyrrolizidine 251O in A. grandidieri represents the first ponerine ant proposed as a dietary source of poison frog alkaloids. Endemic Malagasy ants with defensive alkaloids (with the exception of Paratrechina) are not closely related to any Neotropical species sharing similar chemical defenses. Our results suggest convergent evolution for the acquisition of defensive alkaloids in these dietary ants, which may have been the critical prerequisite for subsequent convergence in poison frogs between Madagascar and the Neotropics.

alkaloid occurrence | dietary sequestration | nicotine

 

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Author contributions: V.C.C. and C.J.R. designed research; V.C.C., V.R., P.S., and B.L.F. performed research; V.C.C. analyzed data; and V.C.C. and C.J.R. wrote the paper.
This paper was submitted directly (Track II) to the PNAS office.

Abbreviations: ds, disubstituted; SpiroP, spiropyrrolizidine; Saha, Sahavondrona; Vato, Vatoharanana; GCT, GC-TOF mass spectrometer; TAS, transcutaneous amphibian stimulator.

To whom correspondence should be sent at the present address: Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853. E-mail: vcc4@cornell.edu.

© 2005 by The National Academy of Sciences of the USA"

 

Convergent Evolution in the Fossil Record:

1. Macroevolutionary interplay between planktic larvae and benthic predators

Kevin J. Peterson1

1 Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA

"Many marine invertebrates have a complex life cycle in which the egg develops into an intermediate planktic larval form rather than developing directly to the benthic juvenile stage. Because of the evolutionary and ecological complexity of pelagic-benthic life cycles, the reasons behind the origin of larvae and their subsequent maintenance over geological time are not well understood. Using both a molecular clock and the fossil record, I show that the initial exploitation of the predator-free pelagic realm by lecithotrophic larvae was achieved independently multiple times by the end of the Early Cambrian, and that the convergent evolution of planktotrophy from lecithotrophic ancestors evolved between the latest Cambrian and Middle Ordovician at least four, and possibly as many as eight, times. Both the exploitation of the pelagic realm by nonfeeding larvae and the acquisition of planktotrophy correlate in time with novel modes of benthic predation, including the dramatic rise in the number and type of epifaunal suspension feeders in the Early Ordovician."

2. A gliding lizard from the Early Cretaceous of China

Pi-Peng Li*, Ke-Qin Gao{dagger}, Lian-Hai Hou*,{ddagger}, and Xing Xu*,{ddagger},§

Shenyang Normal University, Shenyang 110034, People's Republic of China; Peking University, School of Earth and Space Sciences, Beijing 100871, People's Republic of China; and Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, People's Republic of China

Edited by David B. Wake, University of California, Berkeley, CA, and approved February 7, 2007 (received for review October 27, 2006)

"Gliding is an energetically efficient mode of locomotion that has evolved independently, and in different ways, in several tetrapod groups. Here, we report on an acrodontan lizard from the Early Cretaceous Jehol Group of China showing an array of morphological traits associated with gliding. It represents the only known occurrence of this specialization in a fossil lizard and provides evidence of an Early Cretaceous ecological diversification into an aerial niche by crown-group squamates. The lizard has a dorsal-rib-supported patagium, a structure independently evolved in the Late Triassic basal lepidosauromorph kuehneosaurs and the extant agamid lizard Draco, revealing a surprising case of convergent evolution among lepidosauromorphans. A patagial character combination of much longer bilaterally than anteroposteriorly, significantly thicker along the leading edge than along the trailing edge, tapered laterally to form a wing tip, and secondarily supported by an array of linear collagen fibers is not common in gliders and enriches our knowledge of gliding adaptations among tetrapods."

 

Convergent Insect Behaviors:

1. The evolution of fungus-growing termites and their mutualistic fungal symbionts

" Duur K. Aanen , Paul Eggleton , Corinne Rouland-Lefèvre ¶, Tobias Guldberg-Frøslev ||, Søren Rosendahl || and Jacobus J. Boomsma

Department of Population Ecology, Zoological Institute, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark; Entomology Department, The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom;¶ Laboratoire d'Ecophysiologie des Invertébrés, University of Paris-XII-Val de Marne, 61, Avenue du Général de Gaulle, 94010 Créteil Cedex, France; and ||Department of Mycology, Botanical Institute, Øster Farimagsgade 2D, 1353 Copenhagen, Denmark

Edited by Charles D. Michener, University of Kansas, Lawrence, KS, and approved September 5, 2002 (received for review May 24, 2002)

We have estimated phylogenies of fungus-growing termites and their associated mutualistic fungi of the genus Termitomyces using Bayesian analyses of DNA sequences. Our study shows that the symbiosis has a single African origin and that secondary domestication of other fungi or reversal of mutualistic fungi to a free-living state has not occurred. Host switching has been frequent, especially at the lower taxonomic levels, and nests of single termite species can have different symbionts. Data are consistent with horizontal transmission of fungal symbionts in both the ancestral state of the mutualism and most of the extant taxa. Clonal vertical transmission of fungi, previously shown to be common in the genus Microtermes (via females) and in the species Macrotermes bellicosus (via males) [Johnson, R. A., Thomas, R. J., Wood, T. G. & Swift, M. J. (1981) J. Nat. Hist. 15, 751–756], is derived with two independent origins. Despite repeated host switching, statistical tests taking phylogenetic uncertainty into account show a significant congruence between the termite and fungal phylogenies, because mutualistic interactions at higher taxonomic levels show considerable specificity. We identify common characteristics of fungus-farming evolution in termites and ants, which apply despite the major differences between these two insect agricultural systems. We hypothesize that biparental colony founding may have constrained the evolution of vertical symbiont transmission in termites but not in ants where males die after mating.

 

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To whom correspondence should be addressed. E-mail: dkaanen@zi.ku.dk.
This paper was submitted directly (Track II) to the PNAS office.

Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. AY127701–AY127852)."

 

2. New study rewrites evolutionary history of vespid wasps

"Diana Yates, Life Sciences Editor
217-333-5802; diya@uiuc.edu


Released 3/1/07

CHAMPAIGN, Ill. — Scientists at the University of Illinois have conducted a genetic analysis of vespid wasps that revises the vespid family tree and challenges long-held views about how the wasps’ social behaviors evolved. In the study, published in the Feb. 21 Proceedings of the National Academy of Sciences, the researchers found genetic evidence that eusociality (the reproductive specialization seen in some insects and other animals) evolved independently in two groups of vespid wasps.

These findings contradict an earlier model of vespid wasp evolution, which placed the groups together in a single lineage with a common ancestor.

Eusocial behavior is quite rare, and generally involves the breeding of different reproductive classes within a colony. The sterile members of the group perform tasks that support their fertile counterparts. Eusociality occurs in only a few species of insects, rodents, crustaceans and other arthropods.

The evolution of eusociality in wasps has long been a source of debate, said U. of I. entomology graduate student Heather Hines and entomology professor Sydney Cameron, who is the principal investigator of the study. A prior model of vespid wasp evolution placed three subfamilies of wasps – the Polistinae, Vespinae and Stenogastrinae – together in a single evolutionary group with a common ancestor. This model did not rely on a genetic analysis of the wasps, but instead classified them according to several physical and behavioral traits.

Cameron’s team included University of Missouri biology professor James H. Hunt, an expert on the evolution of social behavior in the vespid wasps. Hunt observed that many behavioral characteristics of the vespid wasps contradicted this model of the vespid family tree.

Hunt’s observations, along with those of other behavioral experts in the field, prompted the new analysis.

Instead of affirming a linear, step-wise evolution of social behavior from solitary to highly social, Cameron said, her team’s analysis shows that the Polistinae and Vespinae wasp subfamilies evolved their eusocial characteristics separately from the eusocial Stenogastrinae subfamily of vespid wasps.

Experts on vespid wasp behavior have long noted the significant behavioral differences between the Stenogastrinae subfamily and the group that includes Polistinae and Vespinae. And others have tried, unsuccessfully, to challenge the earlier non-genetic model of vespid wasp evolution. In 1998, German researchers J. Schmitz and R. Moritz also used a genetic analysis to propose that the subfamily Stenogastrinae was evolutionarily distinct from the Polistinae and Vespinae subfamilies.

Proponents of the non-genetic model criticized their work, however, because it relied on an analysis of less than 600 base pairs from two genes (one ribosomal RNA, the other mitochondrial DNA) and included very few representative species, some of which were unsuitable for the analysis.

The new study examined variations in fragments of four genes across 30 species of vespid wasps. Four independent statistical analyses tested the reliability of the pattern of relationships that emerged from the data.

This work confirms the ideas of Schmitz and Moritz, said Cameron, by adding to the weight of evidence that their hypothesis was accurate.

The fact that eusociality evolved independently in two groups of vespid wasps also sheds light on the complexity of evolutionary processes, Cameron said.

“Scientists attempt to make generalizations and simplify the world. But the world isn’t always simple and evolution isn’t simple. This finding points to the complexity of life.”

Convergent Insect Structures:

1. Raptorial Forelimbs:

  • “…be it the example of convergence between the raptorial forelimbs of the praying mantis and the neuropteran Mantispa (Ulrich 1965…” (GD:336).

 

2. Convergent Evolution of Insect Hearing Organs from a Preadaptive Structure

Reinhard Lakes-Harlan, Heiko Stolting, Andreas Stumpner
Proceedings: Biological Sciences, Vol. 266, No. 1424
(Jun. 7, 1999), pp. 1161-1167

Abstract:

"Flies of the taxon Emblemasomatini (Sarcophagidae: Diptera) independently evolved an ear with the same anatomy and location as the Ormiini (Tachinidae: Diptera). Both ears represent a first case of convergent evolution of homologous insect ears, which raises the question for a preadaptation. Physiological and anatomical data indicate a preadaptive-sound-insensitive, but vibration-sensitive scolopidial chordotonal organ in non-hearing flies. As selective pressure for the evolutionary transformation from a vibration receiver into a sound receiver, fast and precise cues for the localization and detection of the sound producing hosts can be presumed."

 

Convergent Plant Structures:

  • "Convergent developments have occurred in many animal taxa, but they also occur among plants" (WEI:222).

1.  Molecular relationships, biogeography, and evolution of Gondwanan Campylopus species (Dicranaceae, Bryopsida)

"Title: Molecular relationships, biogeography, and evolution of Gondwanan Campylopus species (Dicranaceae, Bryopsida)
Author(s): Stech M, Wagner D
Source: TAXON 54 (2): 377-382 MAY 2005
Document Type: Article
Language: English
Cited References: 22      Times Cited: 0       

Abstract: Circumscription, intraspecific variation, and biogeography of five Campylopus species of putative Gondwanan origin, C. flexuosus, C. fragilis, C. pyriformis, C. savannarum, and C. thwaitesii, are evaluated based on parsimony and likelihood analyses of nuclear ribosomal ITS1/ITS2 and chloroplast atpB-rbcL spacer sequences, and are compared with those of C. introflexus and C. pilifer. Campylopus introflexus and C thwaitesii are monophyletic with low intraspecific sequence variation; specimens of C savannarum appear on one well-supported clade together with two closely related species. In contrast, specimens of C. flexuosus, C. fragilis, C pilifer, and C.pyriformis do not form monophyletic groups but are spread over several clades, which partly correspond to geographical regions. Apparently, these morphologically defined species are comprised of groups of populations that are morphologically similar due to convergent evolution. It is concluded that the circumscription and distribution patterns of these widespread Campylopus species are to be revised.

Author Keywords: atpB-rbcL spacer; biogeography; Campylopus; Gondwanan species; ITS; molecular relationships

KeyWords Plus: TAXONOMY; DNA
Addresses: Stech M (reprint author), Free Univ Berlin, Inst Biol Systemat Bot & Pflanzengeog, Altensteinstr 6, Berlin, D-14195 Germany
Free Univ Berlin, Inst Biol Systemat Bot & Pflanzengeog, Berlin, D-14195 Germany
E-mail Addresses: mstech@zedat.fu-berlin.de
Publisher: INT ASSOC PLANT TAXONOMY, C/O UNIV VIENNA, INST BOTANY, RENNWEG 14, A-1030 VIENNA, AUSTRIA
Subject Category: EVOLUTIONARY BIOLOGY; PLANT SCIENCES
IDS Number: 938JS

ISSN: 0040-0262 "


2. "The various kinds of cactus in America are paralleled by analogs among the Euphorbiaceae of Africa" (WEI:222-223).

Molecular Convergence:

1. Convergent Evolution of antifreeze glycoproteins in Antarctic nototheniod Fish and Arctic Cod.

"Convergent evolution of antifreeze glycoproteins in Antarctic notothenioid fish and Arctic cod.

Chen L, DeVries AL, Cheng CH.

Department of Molecular and Integrative Physiology, University of Illinois , Urbana 61801 , USA .

Antarctic notothenioid fishes and several northern cods are phylogenetically distant (in different orders and superorders), yet produce near-identical antifreeze glycoproteins (AFGPs) to survive in their respective freezing environments. AFGPs in both fishes are made as a family of discretely sized polymers composed of a simple glycotripeptide monomeric repeat. Characterizations of the AFGP genes from notothenioids and the Arctic cod show that their AFGPs are both encoded by a family of polyprotein genes, with each gene encoding multiple AFGP molecules linked in tandem by small cleavable spacers. Despite these apparent similarities, detailed analyses of the AFGP gene sequences and substructures provide strong evidence that AFGPs in these two polar fishes in fact evolved independently. First, although Antarctic notothenioid AFGP genes have been shown to originate from a pancreatic trypsinogen, Arctic cod AFGP genes share no sequence identity with the trypsinogen gene, indicating trypsinogen is not the progenitor. Second, the AFGP genes of the two fish have different intron-exon organizations and different spacer sequences and, thus, different processing of the polyprotein precursors, consistent with separate genomic origins. Third, the repetitive AFGP tripeptide (Thr-Ala/Pro-Ala) coding sequences are drastically different in the two groups of genes, suggesting that they arose from duplications of two distinct, short ancestral sequences with a different permutation of three codons for the same tripeptide. The molecular evidence for separate ancestry is supported by morphological, paleontological, and paleoclimatic evidence, which collectively indicate that these two polar fishes evolved their respective AFGPs separately and thus arrived at the same AFGPs through convergent evolution.

MeSH Terms:
  • Amino Acid Sequence
  • Animals
  • Antarctic Regions
  • Antifreeze Proteins
  • Arctic Regions
  • Base Sequence
  • Evolution, Molecular*
  • Fishes/genetics*
  • Glycoproteins/genetics*
  • Molecular Sequence Data
  • Research Support , U.S. Gov't, Non-P.H.S.

Substances:

  • Antifreeze Proteins
  • Glycoproteins

Secondary Source ID:

  • GENBANK/U43149
  • GENBANK/U43200
  • GENBANK/U77676

PMID: 9108061 [PubMed - indexed for MEDLINE]"

2. Convergent Evolution of intertebrate defensins and nematode antibacterial factors

Trends in Microbiology
Volume 13, Issue 7 , July 2005, Pages 314-319

"Oren Froy

Institute of Biochemistry, Food Science and Nutrition, Faculty of Agricultural, Food and Environmental Quality, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel

Available online 23 May 2005.

Antibacterial factors (ABFs) are secreted polypeptides that have an important role in the innate immune system of nematodes. Comparison of these polypeptides revealed similarity in bioactivity, protein sequence and 3D structure, suggesting that they originated from a common ancestor. Comparison of gene organization of nematode ABF genes revealed that all except one contain a Phase 0 intron at a conserved location. The intron phase and location are congruent with the postulated intron gain rules, suggesting a gain of intron before duplication and divergence of the ancestral gene. Although nematode ABFs display similarity in activity and structure to invertebrate (arthropod and mollusk) defensins, lack of sequence similarity and the different genomic organization suggest that these two polypeptide families exhibit convergent evolution.

3. Parallel genotypic adaptation: when evolution repeats itself

"Troy E. Wood, John M. Burke2 and Loren H. Rieseberg1

(1)  Indiana University, 1001 E. Third St, Jordan Hall 142, Bloomington, IN, 47405, U.S.A
(2)  Department of Biological Sciences, Vanderbilt University, VU Station B 351634, Nashville, TN, 37235, U.S.A

Received: 01 January 2002  Accepted: 13 February 2003  

Abstract  Until recently, parallel genotypic adaptation was considered unlikely because phenotypic differences were thought to be controlled by many genes. There is increasing evidence, however, that phenotypic variation sometimes has a simple genetic basis and that parallel adaptation at the genotypic level may be more frequent than previously believed. Here, we review evidence for parallel genotypic adaptation derived from a survey of the experimental evolution, phylogenetic, and quantitative genetic literature. The most convincing evidence of parallel genotypic adaptation comes from artificial selection experiments involving microbial populations. In some experiments, up to half of the nucleotide substitutions found in independent lineages under uniform selection are the same. Phylogenetic studies provide a means for studying parallel genotypic adaptation in non-experimental systems, but conclusive evidence may be difficult to obtain because homoplasy can arise for other reasons. Nonetheless, phylogenetic approaches have provided evidence of parallel genotypic adaptation across all taxonomic levels, not just microbes. Quantitative genetic approaches also suggest parallel genotypic evolution across both closely and distantly related taxa, but it is important to note that this approach cannot distinguish between parallel changes at homologous loci versus convergent changes at closely linked non-homologous loci. The finding that parallel genotypic adaptation appears to be frequent and occurs at all taxonomic levels has important implications for phylogenetic and evolutionary studies. With respect to phylogenetic analyses, parallel genotypic changes, if common, may result in faulty estimates of phylogenetic relationships. From an evolutionary perspective, the occurrence of parallel genotypic adaptation provides increasing support for determinism in evolution and may provide a partial explanation for how species with low levels of gene flow are held together.

  Troy E. Wood
Email: trowood@indiana.edu
Phone: +1-812-856-4996
Fax: +1-812-855-6705

References

Andreev, D., Kreitman, M., Phillips, T.W., Beeman, R.W., ffrench-Constant, R.H. (1999) "Multiple origins of cyclodiene insecticide resistance in Tribolium castaneum (Coleoptera: Tenbrionidae)" J. Mol. Evol. 48: 615-624"

 

4. The molecular evolution of pancreatic ribonuclease

Jaap J. Beintema1, Wim Gaastra1, Johannes A. Lenstra1, Gjalt W. Welling1 and Walter M. Fitch2

(1)  Biochemisch Laboratorium, Rijksuniversiteit, Groningen, The Netherlands
(2)  Department of Physiological Chemistry, University of Wisconsin, 53706 Madison, WI, USA

Received: 5 February 1977  Revised: 17 April 1977  

The primary structures of pancreatic ribonucleases from 26 species (18 artiodactyls, horse, whale, 5 rodents and turtle) are known. Several species contain identical ribonucleases (cow/bison; sheep/goat), other species show polymorphism (arabian camel) or the presence of two structural gene loci (guinea pig pancreas contains two ribonucleases that differ at 31 positions). 26 different sequences (including the ribonuclease from bovine seminal plasma which is paralogous to the pancreatic ribonucleases) were used to construct a most parsimonious tree. A second tree that most closely approximates current biological opinion requires 402 whereas the most parsimonious tree requires 389 nucleotide substitutions. The artiodactyl part of the most parsimonious tree conforms quite well with the biological one of this order, except for the position of the giraffe which is placed with the pronghorn. Other parts of the most parsimonious tree agree less with the biological tree, probably as a result of the occurrence of many parallel and back substitutions. Bovine seminal ribonuclease was found to be the result of a gene duplication which occurred before the divergence of the true ruminants, but after the divergence of this group from the cameloids.

The evolutionary rate of ribonuclease was found to be 390, 3.0 and 11 nucleotide substitutions per 109 yrs per ribonuclease gene, codon and covarion respectively. However, there is much variation in evolutionary rate in different taxa. Values ranging from about 100 (in the bovidae) to about 700 (in the rodents) nucleotide substitutions per 109 yrs per gene were found.

A method for counting parallel and back mutations is presented. The 389 nucleotide substitutions in the most parsimonious tree occur at 88 codon positions; 154 of them are the result of parallel and back mutations. Parallel evolution to a similar structure, including the presence of 2 sites with carbohydrate, was demonstrated in an extensive region at the surface of pig and guinea pig ribonuclease B. The presence of carbohydrate probably is important in a number of species. A correlation between the presence of heavily glycosidated ribonucleases and coecal digestion was observed. Hypothetical sequences of ancestral ungulate ribonucleases contain many recognition sites for carbohydrate attachment; this suggests that herbivores with coecal digestion might have preceded the true ruminants in mammalian evolution.

 

5. “…and even the independent evolution of a protein that prevents ice-crystal formation in the tissues of unrelated Arctic and Antarctic fish (Chen et al. 1997) (GD:336).

 

6. The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes

Abstract:

"Recent molecular phylogenetic studies revealed the extraordinary diversity of single-celled eukaryotes. However, the proper assessment of this diversity and accurate reconstruction of the eukaryote phylogeny are still impeded by the lack of molecular data for some major groups of easily identifiable and cultivable protists. Among them, amoeboid eukaryotes have been notably absent from molecular phylogenies, despite their diversity, complexity, and abundance. To partly fill this phylogenetic gap, we present here combined small-subunit ribosomal RNA and actin sequence data for the three main groups of "Heliozoa" (Actinophryida, Centrohelida, and Desmothoracida), the heliozoan-like Sticholonche, and the radiolarian group Polycystinea. Phylogenetic analyses of our sequences demonstrate the polyphyly of heliozoans, which branch either as an independent eukaryotic lineage (Centrohelida), within stramenopiles (Actinophryida), or among cercozoans (Desmothoracida), in broad agreement with previous ultrastructure-based studies. Our data also provide solid evidence for the existence of the Rhizaria, an emerging supergroup of mainly amoeboid eukaryotes that includes desmothoracid heliozoans, all radiolarians, Sticholonche, and foraminiferans, as well as various filose and reticulose amoebae and some flagellates.

 

--------------------------------------------------------------------------------
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: BV, bootstrap support value; ML, maximum likelihood; PP, posterior probability; SSU rRNA, small-subunit ribosomal RNA.

Data deposition: The sequences reported in this paper have been deposited in the GenBank/EMBL database (accession nos. AY268041–AY26843, AY268045, AY283744–AY283746, AY283754–AY283762, AY305008–AY305013, and AY507123–AY507125).

To whom correspondence should be addressed. E-mail: jan.pawlowski@zoo.unige.ch."



7. Convergent evolution of molecules in electric fish

"March 2, 2006

AUSTIN, Texas—Having a set of extra genes gave fish on separate continents the ability to evolve electric organs, report researchers from The University of Texas at Austin.

Dr. Harold Zakon and colleagues, in a paper recently published in Proceedings of the National Academy of Sciences, show that African and South American groups of fish independently evolved electric organs by modifying sodium channel proteins typically used in muscle contraction.

Mutations in sodium channel proteins can cause serious muscular disorders, epilepsy and heart problems in humans and other vertebrates.

But fish have two copies of many of their genes, and Zakon found that the duplicate sodium channel gene could mutate and evolve without harming the fish.

“The spare gene gave [the electric fish] a little bit of evolutionary leeway,” says Zakon, professor of neurobiology. “This is really one of the first cases that the ancestral gene duplication in fish has actually been linked to a gene that has been freed up and evolving in accordance with a ‘new lifestyle.’”

Zakon and colleagues looked at two sodium channel genes in the electric organs and muscles in electric and non-electric fish. Electric fish use their electric organs, which are modified muscles, to communicate with each other and sense their environment.

The researchers found that electric fishes expressed one of the sodium channel genes in their electric organs only, while non-electric fish express both genes in their muscles.

“Most fish have both genes in the muscle, but as the new electric organ was evolving, the sodium channel—by being lost from the muscle—became devoted to the electric organ,” Zakon says. “So two times, independently, the gene has been ‘lost’ from the muscle. It’s no longer able to turn on in a cell that for millions of years it turned on in, and now it’s turning on in this new organ.”

When the research team looked at the sodium channel protein sequences, they found that some of the mutations occurred at the same or very close to sites in the protein where mutations have been shown to cause disease in humans.

“Functionally important parts of this molecule are changing in order to change the electrical discharge in the fish—changes that would be detrimental in a human muscle,” says Zakon.

Looking at the convergent evolution of sodium channels in these fish helps neurobiologists identify important parts of these proteins relevant to human health, adds Zakon.

“When natural selection is acting to cause changes in a part of a molecule, you know it’s functionally important,” he says. “Natural selection can start showing you the important parts of molecules. We took the evolutionary approach, which is very compatible with the clinical approach.”
The research team included evolutionary biologist Dr. David Hillis, graduate student Derrick Zwickl and research associate Ying Lu.

For more information contact: Harold Zakon, 512-471-0194."

 

8. Research updates 65-year-old genetic discovery

"Gene variants determine which humans and which chimpanzees can taste bitter substances. For humans, this taste sensitivity may influence nutritional choices (and, ultimately, their health), as well as behaviors such as smoking. For chimpanzees, it provides a way to live safely in their environments by avoiding toxic plants and other harmful compounds.

Research conducted more 65 years ago by a team of scientists led by British statistician and geneticist Sir Ronald Aylmer Fisher concluded that this gene variant was the same in humans and chimpanzees and existed throughout time – an example of balancing selection. Their findings were published in 1939 in Nature, one of the world's leading science journals.

A new team of researchers – including Anne Stone, an anthropological geneticist at ASU – writes in the cover story of the April 13 edition of Nature that, while the observations made by Fisher and his team were accurate, “their explanation was wrong.” Instead of being an example of balancing selection, the researchers conclude that humans and chimpanzees have gene variants, but for different reasons – and is an example of convergent evolution.

It was just a few years ago, in 2003, that sensitivity to a bitter compound known as phenylthiocarbamide (PTC) was mapped in human genes.

“That gene was found to be controlling whether you can taste PTC or not,” says Stone, an associate professor in ASU's School of Human Evolution & Social Change in the College of Liberal Arts and Sciences.

“We decided to look at this in chimpanzees and see if Fisher was right,” she says.

The “we” includes authors of the report Stephen Wooding, Michael T. Howard, Diane M. Dunn, Robert B. Weiss and Michael J. Bamshad in the Department of Human Genetics at the University of Utah; Bernd Bufe and Wolfgang Meyerhof of the German Institute of Human Nutrition Postdam-Rehbruecke; and Christina Grassi and Maribel Vazquez in the Department of Comparative Medicine at the Southwest Foundation for Biomedical Research.

Stone, who works on applications of population genetics to questions concerning the origins, population history and evolution of humans and the great apes, sent DNA samples of each of three subspecies of chimpanzees to the University of Utah.

“No chimpanzees were harmed to obtain the samples,” Stone says.

The DNA is provided by veterinarians and comes from either blood samples or cheek swabs. She uses these samples to help zoos, sanctuaries and primate centers identify subspecies of chimpanzees.

“My goal is to better understand chimpanzees in their own right, and to ultimately help with their preservation,” she says.

Her samples contributed to this latest research, which found that, when compared to human non-taster gene variants, “chimps don't have the same change in the middle of the gene variant as humans, but rather have a change at the start.” Both changes in the sequences nullify this bitter taste receptor. These are the findings that demonstrate that, while some humans and some chimpanzees cannot taste this bitter substance, the reasons why are different.

This new information can be used by researchers to understand bitter-taste receptors, and how having particular bitter-taste receptors affect nutrition and health, Stone says.

With this Nature cover story, Stone joins a growing list of researchers from ASU's College of Liberal Arts and Sciences whose research has made the cover of either Nature or Science this academic year.

While that's an exceptional achievement in itself, what's noteworthy is that three of the researchers are junior faculty members. Stone, an associate professor, joins Gro Amdam and Kevin McGraw, both assistant professors, on the list. Amdam and McGraw are in the college's School of Life Sciences.

Amdam's research found a link between social behavior and maternal traits in bees. A paper describing her experiments was the cover story of the Jan. 5 issue of Nature, which she wrote with M. Kim Fondrk and Robert Page from ASU, and Angela Csondes from the University of California-Davis. Fondrk is a program manager, and Page is a professor and director in the School of Life Sciences.

McGraw's research showed that the female North American barn swallow, even after pairing with a male, still “comparison shops” for sexual partners. His study was featured on the Sept. 30 cover of the journal Science.

Carol Hughes, carol.hughes@asu.edu

(480) 965-6375"

9. Convergent Evolution of Receptors for Protein Import into Mitochondria

"Background

Mitochondria evolved from intracellular bacterial symbionts. Establishing mitochondria as organelles required a molecular machine to import proteins across the mitochondrial outer membrane. This machinery, the TOM complex, is composed of at least seven component parts, and its creation and evolution represented a sizeable challenge. Although there is good evidence that a core TOM complex, composed of three subunits, was established in the protomitochondria, we suggest that the receptor component of the TOM complex arose later in the evolution of this machine.

Results

We have solved by nuclear magnetic resonance the structure of the presequence binding receptor from the TOM complex of the plant Arabidopsis thaliana. The protein fold suggests that this protein, AtTom20, belongs to the tetratricopeptide repeat (TPR) superfamily, but it is unusual in that it contains insertions lengthening the helices of each TPR motif. Peptide titrations map the presequence binding site to a groove of the concave surface of the receptor. In vitro functional assays and peptide titrations suggest that the plant Tom20 is functionally equivalent to fungal and animal Tom20s.

Conclusions

Comparison of the sequence and structure of Tom20 from plants and animals suggests that these two presequence binding receptors evolved from two distinct ancestral genes following the split of the animal and plant lineages. The need to bind equivalent mitochondrial targeting sequences and to make similar interactions within an equivalent protein translocation machine has driven the convergent evolution of two distinct proteins to a common structure and function."

10. Sodium channel genes and the evolution of diversity in communication signals of electric fishes: Convergent molecular evolution

"Harold H. Zakon, Ying Lu, Derrick J. Zwickl, and David M. Hillis

Sections of Neurobiology and Integrative Biology and Center for Computational Biology and Bioinformatics, University of Texas, Austin, TX 78712; and Bay Paul Center for Comparative and Molecular Biology, Marine Biological Laboratory, Woods Hole, MA 02543

Communicated by Gene E. Robinson, University of Illinois at Urbana–Champaign, Urbana, IL, January 6, 2006 (received for review November 10, 2005)

We investigated whether the evolution of electric organs and electric signal diversity in two independently evolved lineages of electric fishes was accompanied by convergent changes on the molecular level. We found that a sodium channel gene (Nav1.4a) that is expressed in muscle in nonelectric fishes has lost its expression in muscle and is expressed instead in the evolutionarily novel electric organ in both lineages of electric fishes. This gene appears to be evolving under positive selection in both lineages, facilitated by its restricted expression in the electric organ. This view is reinforced by the lack of evidence for selection on this gene in one electric species in which expression of this gene is retained in muscle. Amino acid replacements occur convergently in domains that influence channel inactivation, a key trait for shaping electric communication signals. Some amino acid replacements occur at or adjacent to sites at which disease-causing mutations have been mapped in human sodium channel genes, emphasizing that these replacements occur in functionally important domains. Selection appears to have acted on the final step in channel inactivation, but complementarily on the inactivation "ball" in one lineage, and its receptor site in the other lineage. Thus, changes in the expression and sequence of the same gene are associated with the independent evolution of signal complexity.

To whom correspondence should be addressed. E-mail: h.zakon@mail.utexas.edu"

 

11. Independent evolution of bitter-taste sensitivity in humans and chimpanzees

Stephen Wooding1, Bernd Bufe2, Christina Grassi3, Michael T. Howard1, Anne C. Stone4, Maribel Vazquez3, Diane M. Dunn1, Wolfgang Meyerhof2, Robert B. Weiss1 and Michael J. Bamshad1,5
Top of page

"It was reported over 65 years ago that chimpanzees, like humans, vary in taste sensitivity to the bitter compound phenylthiocarbamide (PTC)1. This was suggested to be the result of a shared balanced polymorphism, defining the first, and now classic, example of the effects of balancing selection in great apes. In humans, variable PTC sensitivity is largely controlled by the segregation of two common alleles at the TAS2R38 locus, which encode receptor variants with different ligand affinities2, 3, 4. Here we show that PTC taste sensitivity in chimpanzees is also controlled by two common alleles of TAS2R38; however, neither of these alleles is shared with humans. Instead, a mutation of the initiation codon results in the use of an alternative downstream start codon and production of a truncated receptor variant that fails to respond to PTC in vitro. Association testing of PTC sensitivity in a cohort of captive chimpanzees confirmed that chimpanzee TAS2R38 genotype accurately predicts taster status in vivo. Therefore, although Fisher et al.'s observations1 were accurate, their explanation was wrong. Humans and chimpanzees share variable taste sensitivity to bitter compounds mediated by PTC receptor variants, but the molecular basis of this variation has arisen twice, independently, in the two species.

1. Department of Human Genetics, University of Utah, 15 North 2030 East, Salt Lake City, Utah 84112-5330, USA
2. German Institute of Human Nutrition Potsdam-Rehbruecke, Arthur-Scheunert-Allee 114-116, Nuthetal 14558, Germany
3. Department of Comparative Medicine, Southwest Foundation for Biomedical Research, San Antonio, Texas 78245-0549, USA
4. School of Human Evolution and Social Change, Arizona State University, Tempe, Arizona 85287-2402, USA
5. †Present address: Departments of Pediatrics and Genome Sciences, University of Washington, Seattle, Washington 98195, USA

Correspondence to: Stephen Wooding1Michael J. Bamshad1,5 Correspondence and requests for materials should be addressed to S.W. (Email: swooding@genetics.utah.edu) or M.J.B. (Email: mbamshad@u.washington.edu).

Received 17 November 2005 | Accepted 16 February 2006"

12. Parallel evolution: proteins do it, too

"June 12, 2006


Parallel evolution: proteins do it, too

ANN ARBOR, Mich.—Wings, spines, saber-like teeth—nature and the fossil record abound with examples of structures so useful they've evolved independently in a variety of animals. But scientists have debated whether examples of so-called adaptive, parallel evolution also can be found at the level of genes and proteins.

In the June 11 issue of Nature Genetics, evolutionary biologist Jianzhi (George) Zhang presents evidence for one such instance in a gene for an enzyme that helps leaf-eating monkeys digest their food.

"We know that parallel, or convergent, evolution is very common at the level of morphology—birds can fly, insects can fly, bats can fly, and they've all evolved this capability independently. But at the DNA and protein sequence level, it's very rare to find parallel evolution. This paper provides a real example," said Zhang, an associate professor of ecology and evolutionary biology.

The new work builds on previous research in which Zhang showed that the duplication of a gene encoding a pancreatic enzyme helped Asian colobine monkeys cope with an unusual diet.

"Colobines are different from other monkeys in that they primarily eat leaves rather than fruit or insects, and leaves are very difficult to digest," Zhang said. The monkeys manage with a digestive system similar to a cow's. Bacteria in the gut ferment the leaves and take up nutrients that are released in the process. The monkeys, in turn, digest the bacteria to recover the nutrients, such as protein and ribonucleic acid (RNA), a particularly important source of nitrogen in leaf eaters.

Zhang focused his attention on RNASE1, a pancreatic enzyme that breaks down bacterial RNA. Most primates have one gene encoding the enzyme, but he found that the douc langur, a colobine from Asia, has two—one encodes RNASE1, and its duplicate encodes a new enzyme, RNASE1B. The duplicate enzyme, it turns out, works better than the original in the acidic conditions of the colobine small intestine, making it more efficient at recovering nutrients from bacteria.

Zhang's initial analysis showed that the duplication occurred about four million years ago, some nine million years after the two main groups of colobines—Asian and African—split into separate lineages. To confirm that the duplication occurred after the split, he analyzed DNA samples from an African colobine known as the guereza or colobus monkey.

"We sequenced the gene, and to our surprise we found not one, not two, but three RNASE1 genes," Zhang said. "Further analysis showed that the duplications in African monkeys and Asian monkeys were separate, independent events." Next, Zhang wanted to know if the duplications resulted in similar functional changes in the enzyme. Just as in the Asian colobine, the duplicated genes in African colobines functioned more efficiently at the typical acidity level of the colobine small intestine, he found.

"Then our question was whether the similar functional changes were due to identical amino acid changes at the protein sequence level," Zhang said. "Indeed, we found three amino acid changes that were identical in the two lineages. They occurred independently, but they were identical." Additional experiments confirmed that the three, independent, parallel amino acid changes were responsible for the change in enzyme function.

In both Asian and African colobines, the original, less efficient, gene is not discarded after duplication. But why, Zhang wondered.

"The guess is that the old copy is still doing something important," he said. "RNASE1 has another function, which is to degrade double-stranded RNA. Double-stranded RNA is not normally found in food, but it's found in some viruses, so the old gene may be useful in defending against viral infection." Zhang checked the new and old genes in both lineages and found the same pattern: the new genes have lost the ability to degrade double-stranded RNA, but the older genes have kept it.

"So it looks like, after gene duplication, there is a division of labor," Zhang said. "Before duplication, the gene is supposed to do both jobs: digestion and degrading double-stranded RNA. After duplication, one copy seems to retain the activity of degrading double-stranded RNA while the other copy has adapted to changed pH in the small intestine so it can better digest food."

Even after clearly demonstrating parallel evolution in this case, Zhang believes the phenomenon is uncommon at the protein sequence level. However, he proposes a list of criteria in the Nature Genetics paper that he and other researchers can use to test apparent examples in the future.

The work was funded by National Institutes of Health.

Jianzhi Zhang

Contact: Nancy Ross-Flanigan
Phone: (734) 647-1853"

 

13. Cell cycle control in bacteria and yeast: a case of convergent evolution?

"Brazhnik P, Tyson JJ.

Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0406, USA. brazhnik@vt.edu

Superficially similar traits in phylogenetically unrelated species often result from adaptation to common selection pressures. Examples of convergent evolution are known at the levels of whole organisms, organ systems, gene networks and specific proteins. The phenotypic properties of living things, on the other hand, are determined in large part by complex networks of interacting proteins. Here we present a mathematical model of the network of proteins that controls DNA synthesis and cell division in the alpha-proteobacterium, Caulobacter crescentus. By comparing the protein regulatory circuits for cell reproduction in Caulobacter with that in budding yeast (Saccharomyces cerevisiae), we suggest that convergent evolution may have created similar molecular reaction networks in order to accomplish the same purpose of coordinating DNA synthesis to cell division. Although the genes and proteins involved in cell cycle regulation in prokaryotes and eukaryotes are very different and (apparently) phylogenetically unrelated, they seem to be wired together in similar regulatory networks, which coordinate cell cycle events by identical dynamical principles."

 

14. Molecular Phylogeny and Evolution of Morphology in the Social Amoebas


Science 27 October 2006:
Vol. 314. no. 5799, pp. 661 - 663
DOI: 10.1126/science.1130670

Molecular Phylogeny and Evolution of Morphology in the Social Amoebas

Pauline Schaap,1 Thomas Winckler,2 Michaela Nelson,3 Elisa Alvarez-Curto,1 Barrie Elgie,3 Hiromitsu Hagiwara,4 James Cavender,5 Alicia Milano-Curto,1 Daniel E. Rozen,1* Theodor Dingermann,6,7 Rupert Mutzel,8 Sandra L. Baldauf3{delta}

"The social amoebas (Dictyostelia) display conditional multicellularity in a wide variety of forms. Despite widespread interest in Dictyostelium discoideum as a model system, almost no molecular data exist from the rest of the group. We constructed the first molecular phylogeny of the Dictyostelia with parallel small subunit ribosomal RNA and a-tubulin data sets, and we found that dictyostelid taxonomy requires complete revision. A mapping of characters onto the phylogeny shows that the dominant trend in dictyostelid evolution is increased size and cell type specialization of fruiting structures, with some complex morphologies evolving several times independently. Thus, the latter may be controlled by only a few genes, making their underlying mechanisms relatively easy to unravel."

 

15. Molecular Evolutionary Convergence of the Flight Muscle Protein Arthrin in Diptera and Hemiptera

Stephan Schmitz*, Christoph J. Schankin*, Heino Prinz§, Rachel S. Curwen*, Peter D. Ashton*, Leo S. D. Caves*, Rainer H. A. Fink, John C. Sparrow*, Peter J. Mayhew* and Claudia Veigel*

* Department of Biology, University of York, York, United Kingdom
National Institute for Medical Research, London, United Kingdom
Department of Physiology and Pathophysiology, University of Heidelberg, Heidelberg, Germany
§ Max Planck Institute of Molecular Physiology, Dortmund, Germany

E-mail: stephan.schmitz@nimr.mrc.ac.uk.

"Uniquely, the asynchronous flight muscle myofibrils of many insects contain arthrin, a stable 1:1 conjugate between actin and ubiquitin. The function of arthrin is still unknown. Here we survey for the presence of arthrin in 63 species of insect across nine orders using Western blotting. Analysis of the evolutionary distribution shows that arthrin has evolved a limited number of times but at least once in the Diptera and once in the Hemiptera. However, the presence of arthrin does not correlate with any observed common features of flight mechanism, natural history, or morphology. We also identify the site of the isopeptide bond in arthrin from Drosophila melanogaster (Diptera) and Lethocerus griseus (Hemiptera) using mass spectrometry. In both species, the isopeptide bond is formed between lysine 118 of the actin and the C-terminal glycine 76 of ubiquitin. Thus, not only the ubiquitination of actin but also the site of the isopeptide bond has evolved convergently in Diptera and Hemiptera. In terms of the actin monomer, lysine 118 is near neither the binding sites of the major actin-binding proteins, myosin, tropomyosin, or the troponins, nor the actin polymerization sites. However, molecular modeling supports the idea that ubiquitin bound to an actin in one F-actin strand might be able to interact with tropomyosin bound to the actin monomers of the other strand and thereby interfere with thin filament regulation."

 

16. Convergent evolution in primates and an insectivore

Dario Boffelli, Jan-Fang Cheng and Edward M. RubinCorresponding Author Contact Information, E-mail The Corresponding Author

Genome Sciences Department, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 84-171, Berkeley, California 94720, USA

Received 19 February 2003; accepted 1 May 2003. ; Available online 15 August 2003.

Abstract:

"The cardiovascular risk factor LPA has a puzzling distribution among mammals, its presence being limited to a subset of primates and a member of the insectivore lineage, the hedgehog. To explore the evolutionary history of LPA, we performed extensive genomic sequence comparisons of multiple species with and without an LPA gene product, such as human, baboon, hedgehog, lemur, and mouse. This analysis indicated that LPA arose independently in a subset of primates, including baboon and human, and an insectivore, the hedgehog, and was not simply lost by species lacking it. The similar structural domains shared by the hedgehog and primate LPA indicate that they were formed by a unique molecular mechanism involving the convergent evolution of paralogous genes in these distant species."

 

17. Convergent evolution of gene circuits

Gavin C Conant & Andreas Wagner

Department of Biology, 167 Castetter Hall, The University of New Mexico, Albuquerque, New Mexico 87131, USA.


Correspondence should be addressed to Andreas Wagner wagnera@unm.edu

Convergent evolution is a potent indicator of optimal design. We show here that convergent evolution occurs in genetic networks. Specifically, we show that multiple types of transcriptional regulation circuitry in Escherichia coli and the yeast Saccharomyces cerevisiae have evolved independently and not by duplication of one or a few ancestral circuits.

Convergent evolution occurs on all levels of biological organization, from organ systems to proteins. For instance, eyes and wings have evolved independently multiple times, and many aquatic vertebrates share a streamlined shape, despite their independent evolutionary origins1. On the smaller scale of proteins, lysozymes have been recruited independently for foregut fermentation in bovids, colubine monkeys and a bird2, 3. Antifreeze glycoproteins in antarctic notothenioids and northern cod (living at opposite ends of the globe) have independently evolved similar amino acid sequences4.

Recent studies have identified abundant genetic circuit motifs in transcriptional regulation networks of the yeast S. cerevisiae5, 6 and the bacterium E. coli6, 7. These circuit motifs include regulatory chains, feed-forward circuits and a 'bi-fan' (Fig. 1). Such motifs may have had two principal evolutionary origins. First, they may have come about through the random duplication and subsequent diversification of a few ancestral circuits. Given the high frequency at which genes and genomes undergo duplication8, this is a plausible scenario. It is equally possible, however, that these circuits arose independently by recruitment of unrelated genes. If such convergent circuit evolution is prevalent, then these circuits owe their abundance to the action of natural selection.

(a) Two indicators of common ancestry for gene circuits. Each of n = 5 circuits of a given type (a feed-forward loop for illustration) is represented as a node in a circuit graph. Nodes are connected if they are derived from a common ancestor, that is, if all k pairs of genes in the two circuits are pairs of duplicate genes. A = 0 if no circuits share a common ancestor (the graph has n isolated vertices); A 1 if all circuits share one common ancestor (the graph is fully connected). The number C of connected components indicates the number of common ancestors (two in the middle panel) from which the n circuits derive. Fmax is the size of the largest family of circuits with a single common ancestor (the graph's largest component). (b) Little common ancestry in six circuit types. We considered two circuits to be related by common ancestry if each pair of genes at corresponding positions in the circuit had significant sequence similarity. Each row of the table shows values of C, A and Fmax for a given circuit type, followed in parentheses by their average values plusminus standard deviations and P values, as defined by a permutation test described in Supplementary Methods online.


To determine the evolutionary origin of transcriptional regulation circuits, we defined two indicators of common circuit ancestry, A and Fmax. Consider a genome containing n regulatory circuits, each with k genes and identical topology (for details see Supplementary Methods online). A pair of circuits shares a common ancestor if all k gene pairs in the circuit pair are gene duplicates. We next defined a 'circuit graph' whose n nodes represent the n circuits and where an edge connects two nodes (circuits) if the circuits have a common ancestor. Our first indicator, A, of common circuit ancestry, is equal to A = 1 - (C/n), where C is the number of components in the graph (Fig. 1a). The greater A is, the greater is the fraction of circuits sharing a common ancestor. Our second indicator is Fmax, the size of the largest family of circuits with common ancestry (Fig. 1a).

We identified duplicate genes using BLASTP9 at a significance threshold of E 10-5 (E values between 10-3 and 10-11 yield the same results). Using this criterion, neither of two circuit types in E. coli showed evidence of common ancestry (A = 0 and Fmax = 1 for both; Fig. 1b). We also studied 18 yeast circuit types, and only three (feed-forward loops, multi-input modules of size 2 and bi-fans) showed evidence of common ancestry (A > 0 and Fmax > 1; Fig. 1b). This may be due to chance alone, however, simply because duplicate genes are abundant in the yeast genome. Therefore, we used permutation tests (described in Supplementary Methods online) to assess the statistical evidence of A and Fmax. For no circuit type was A significantly different from the chance expectation. For example, yeast contains 542 bi-fan motifs with A = 0.197. The probability of observing A = 0.197 by chance is P = 0.18: too large to reject the null hypothesis. We observed a marginally significant value of Fmax = 5 for feed-forward loops (P = 0.05). Even for this circuit type, however, most circuits (43 of 48) showed independent ancestry.

Our analysis of yeast circuits rests on genome-scale chromatin precipitation experiments that use a statistical error threshold (Pe) to identify true regulatory interactions5. The results reported in Figure 1b are based on Pe = 10-3, but we found the same results when varying Pe between 10-2 and 10-5. As above, only feed-forward loops yielded a marginally significant value of A = 0.11 (P = 0.03) and Fmax = 3 (P = 0.03) at Pe 10-4. Lowering Pe further to Pe = 10-5 yielded A = 0 and Fmax = 1.

We also asked whether members of one gene family preferentially occurred in one type of gene circuit. This would be expected if many circuits originated through duplication. Specifically, we asked whether the likelihood of a gene occurring in a given circuit type increases if one of its duplicates occurs in that type. The answer is no (Table 1).

In sum, we found no common ancestry among the E. coli circuit types, the yeast regulatory chains or the yeast multi-input motifs with more than two regulators. Of the remaining three yeast circuit types, two showed common ancestry indistinguishable from that expected by chance. Only feed-forward loops showed marginally significant values of either A or Fmax, but this finding is not statistically robust. Moreover, most (43 of 48) feed-forward loops have clearly independent origins. We also note that the probability of falsely identifying a pair of circuits as duplicates decreases with increasing circuit size. The larger a circuit is, the less evidence of duplication it shows in our analysis.

Multiple lines of evidence indicate that duplicate genes diverge rapidly in function10, 11, 12. Our findings that gene circuits do not share common ancestry and that duplicate regulatory genes are randomly distributed across gene circuit types underscore this point, because they imply that duplicate transcriptional regulators can readily evolve new interactions. The short DNA binding sites of transcriptional regulators account for much of this plasticity. In microbes like yeast and E. coli, new regulatory interactions can arise rapidly13, even on the time scale of laboratory evolution experiments14. Transcriptional regulation circuits are thus ideal systems for studying convergent evolution, because natural selection has much raw material (variation in regulatory interactions) to shape such circuits.

The finding that gene circuits have evolved repeatedly makes a strong case for their optimal design. For example, the design of a feed-forward loop may serve to activate the regulated (downstream) genes only if the farthest-upstream regulator is persistently activated. Moreover, the same design rapidly deactivates genes once this regulator is shut off7. Our results also suggest that convergent evolution, probably rare in protein sequences, may have an important role in the higher organizational level of gene circuits. Stephen Jay Gould famously asked what would be conserved if life's tape, its evolutionary history, was replayed15. Transcriptional regulation circuits, it seems, might come out just about the same.

Note: Supplementary information is available on the Nature Genetics website.

Received 28 March 2003; Accepted 21 May 2003; Published online: 22 June 2003.


REFERENCES

1. Futuyma, D.J. Evolutionary Biology 3rd edn. (Sinauer Associates, Sunderland, Massachusetts, 1998).
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3. Kornegay, J.R., Schilling, J.W. & Wilson, A.C. Mol. Biol. Evol. 11, 921–928 (1994). | PubMed | ISI | ChemPort |
4. Chen, L., DeVries, A.L. & Cheng, C.-H.C. Proc. Natl. Acad. Sci. USA 94, 3817–3822 (1997). | Article | PubMed | ChemPort |
5. Lee, T.I. et al. Science 298, 799–804 (2002). | Article | PubMed | ISI | ChemPort |
6. Milo, R. et al. Science 298, 824–827 (2002). | Article | PubMed | ISI | ChemPort |
7. Shen-Orr, S.S., Milo, R., Mangan, S. & Alon, U. Nat. Genet. 31, 64–68 (2002). | Article | PubMed | ISI | ChemPort |
8. Lynch, M. & Conery, J.S. Science 290, 1151–1155 (2000). | Article | PubMed | ISI | ChemPort |
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10. Wagner, A. Mol. Biol. Evol. 18, 1283–1292 (2001). | PubMed | ISI | ChemPort |
11. Dermitzakis, E.T. & Clark, A.G. Mol. Biol. Evol. 19, 1114–1121 (2002). | PubMed | ISI | ChemPort |
12. Wagner, A. Proc. Natl. Acad. Sci. USA 97, 6579–6584 (2000). | Article | PubMed | ChemPort |
13. Stone, J.R. & Wray, G.A. Mol. Biol. Evol. 18, 1764–1770 (2001). | PubMed | ISI | ChemPort |
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15. Gould, S.J. Wonderful Life: The Burgess Shale and the Nature of History (W.W. Norton, New York, 1989).

 

18. Mcm4,6,7 uses a “pump in ring1 mechanism to unwind DNA by steric exclusion and actively translocate along a duplex


Daniel L. Kaplan, Megan J. Davey, and Mike O'Donnell

Laboratory for DNA Replication, Rockefeller University, New York, NY 10021

Corresponding Author: dkaplan@mod.rockefeller.edu

Mcm4,6,7 is a ring-shaped heterohexamer and the putative eukaryotic replication fork helicase. In this study, we examine the mechanism of Mcm4,6,7. Mcm4,6,7 binds to only one strand of a duplex during unwinding, corresponding to the leading strand of a replication fork. Mcm4,6,7 unwinding stops at a nick in either strand. The Mcm4,6,7 ring also actively translocates along duplex DNA, enabling the protein to drive branch migration of Holliday junctions. The Mcm4,6,7 mechanism is very similar to DnaB, except the proteins translocate with opposite polarity along DNA. Mcm4,6,7 and DnaB have different structural folds and evolved independently; thus, the similarity in mechanism is surprising. We propose a “pump in ring” mechanism for both Mcm4,6,7 and DnaB, wherein a single-strand DNA pump is situated within the central channel of the ring-shaped helicase, and unwinding is the result of steric exclusion. In this example of convergent evolution, the “pump in ring” mechanism was probably selected by eukaryotic and bacterial replication fork helicases in order to restrict unwinding to replication fork structures, stop unwinding when the replication fork encounters a nick, and actively translocate along duplex DNA to accomplish additional activities such as DNA branch migration.

 

19. Molecular adaptation of a leaf-eating bird: stomach lysozyme of the hoatzin

JR Kornegay, JW Schilling and AC Wilson
Department of Molecular and Cell Biology, University of California, Berkeley 94720.

This report describes a lysozyme expressed at high levels in the stomach of the hoatzin, the only known foregut-fermenting bird. Evolutionary comparison places it among the calcium-binding lysozymes rather than among the conventional types. Conventional lysozymes were recruited as digestive enzymes twice in the evolution of mammalian foregut fermenters, and these independently recruited lysozymes share convergent structural changes attributed to selective pressures in the stomach. Biochemical convergence and parallel amino acid replacements are observed in the hoatzin stomach lysozyme even though it has a different genetic origin from the mammalian examples and has undergone more than 300 million years of independent evolution.

 

Convergent Evolution Defined

The Design Significance of Convergence

Convergent Animal Behaviors

Convergent Animal Structures

Convergent Defense Mechanisms


Convergent Evolution in the Fossil Record

Convergent Insect Behaviors

Convergent Insect Structures

Convergent Plant Structures

Molecular Convergence

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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