TingetalPNAS2000 - The phylogeny of closely related species...

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The phylogeny of closely related species as revealed by the genealogy of a speciation gene, Odysseus Chau-Ti Ting*, Shun-Chern Tsaur*, and Chung-I Wu ² Department of Ecology and Evolution, University of Chicago, Chicago, IL 60637 Edited by M. T. Clegg, University of California, Riverside, CA, and approved February 24, 2000 (received for review December 14, 1999) Molecular differentiation between races or closely related species is often incongruent with the reproductive divergence of the taxa of interest. Shared ancient polymorphism and y or introgression during secondary contact may be responsible for the incongruence. At loci contributing to speciation, these two complications should be minimized (1, 2); hence, their variation may more faithfully reflect the history of the species’ reproductive differentiation. In this study, we analyzed DNA polymorphism at the Odysseus ( OdsH ) locus of hybrid sterility between Drosophila mauritiana and Drosophila simulans and were able to verify such a prediction. Interestingly, DNA variation only a short distance away (1.8 kb) appears not to be influenced by the forces that shape the recent evolution of the OdsH coding region. This locus thus may represent a test case of inferring phylogeny of very closely related species. S pecies are delineated by shared reproductive physiology, development, sexual behavior, and morphology (3, 4). Di- vergence in these systems is manifested as hybrid sterility, hybrid inviability, premating isolation, and morphological differences, respectively. Races are less well defined but members often may cluster by morphological traits. One of the paradoxes concerning race or species differentiation is the common occurrences of ambiguity in distinguishing taxa by molecular means, even when grouping by reproductive or morphological traits is straightfor- ward and clearcut. Human racial differentiation may be a most obvious example in which many morphological characters cluster by geographical origin, whereas almost all molecular polymor- phisms are extensively shared among races (5). Morphological distinction among dog breeds is another example (6). In Dro- sophila , sexual isolation between the Zimbabwe and non-African races of Drosophila melanogaster is clearly determined by many genes spread over the autosomal genome (7), and yet, recent molecular data have failed to show much differentiation at autosomal loci (8, 9). An explanation for the discordance between the ‘‘reproduc- tive’’ and ‘‘molecular’’ phylogeny is that genomes may be mosaics with respect to molecular genealogy, as illustrated in Fig. 1. Most loci, chosen without regard to their roles in reproductive differ- entiation, may not reflect the biological divergence in their sequence polymorphism because of either shared ancient poly- morphism or gene introgression through secondary contact (Fig.
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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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TingetalPNAS2000 - The phylogeny of closely related species...

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