Klimanetal_2000 - Copyright 2000 by the Genetics Society of...

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Copyright 2000 by the Genetics Society of America The Population Genetics of the Origin and Divergence of the Drosophila simulans Complex Species Richard M. Kliman,* ,1 Peter Andolfatto, ²,2 Jerry A. Coyne, ‡,3 Frantz Depaulis, §,2 Martin Kreitman, ‡,3 Andrew J. Berry, ‡,4 James McCarter, ‡,5 John Wakeley** ,4 and Jody Hey* * Department of Genetics, Rutgers University, Piscataway, New Jersey 08854-8082, ² Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637, Department of Ecology, Evolution and Behavior, Princeton University, Princeton, New Jersey 08544, § Laboratoire d’Ecologie, Universite ´ Paris 6, CNRS-UMR 7625 Case 237, 75252 Paris Cedex 05, France and ** Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138 Manuscript received April 14, 2000 Accepted for publication September 11, 2000 ABSTRACT The origins and divergence of Drosophila simulans and close relatives D. mauritiana and D. sechellia were examined using the patterns of DNA sequence variation found within and between species at 14 different genes. D. sechellia consistently revealed low levels of polymorphism, and genes from D. sechellia have accumulated mutations at a rate that is z 50% higher than the same genes from D. simulans. At synonymous sites, D. sechellia has experienced a significant excess of unpreferred codon substitutions. Together these observations suggest that D. sechellia has had a reduced effective population size for some time, and that it is accumulating slightly deleterious mutations as a result. D. simulans and D. mauritiana are both highly polymorphic and the two species share many polymorphisms, probably since the time of common ancestry. A simple isolation speciation model, with zero gene flow following incipient species separation, was fitted to both the simulans / mauritiana divergence and the simulans / sechellia divergence. In both cases the model fit the data quite well, and the analyses revealed little evidence of gene flow between the species. The exception is one gene copy at one locus in D. sechellia , which closely resembled other D. simulans sequences. The overall picture is of two allopatric speciation events that occurred quite near one another in time. S EVERAL hundred thousand years ago one species Historically there have been two main approaches to of Drosophila gave rise to three that today we call the genetic study of species divergence. The classical Drosophila simulans , D. mauritiana , and D. sechellia. Today approach is to genetically map traits that are thought the three species are morphologically distinct (primarily to be important in speciation. Such traits tend to fall on the basis of male genitalia), partially intersterile into one of three categories. (male hybrids are sterile, female hybrids fertile), and 1. The most straightforward are those for which the largely allopatric ( D. simulans is a nearly cosmopolitan species exhibit characteristic differences and that human commensal, while the other two are island en- probably represent species-specific adaptations. Ma- demics). The combination of clear phenotypic distinc-
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This note was uploaded on 12/18/2010 for the course GENETICS 486 taught by Professor Hey during the Fall '10 term at Rutgers.

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Klimanetal_2000 - Copyright 2000 by the Genetics Society of...

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