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Integrative and Comparative Biology Advance Access originally published online on May 17, 2008
Integrative and Comparative Biology 2008 48(4):512-519; doi:10.1093/icb/icn041
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© The Author 2008. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oxfordjournals.org.

Evolution of sex chromosomes in Sauropsida

Christopher L. Organ1,* and Daniel E. Janes*
*Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA

Correspondence: 1E-mail: corgan{at}oeb.harvard.edu

Reptiles (sauropsids) represent the sister group to mammals, and the basal members of Reptilia may provide a good model for the condition of the common ancestor of both groups. Sex-determining mechanisms (SDM) and organizations of sex chromosomes among genotypically sex-determining (GSD) species vary widely across reptiles. Birds and snakes, for example, are entirely GSD whereas other reptiles, like all crocodilians, exhibit temperature-dependent sex determination (TSD). Here we explore the evolution of sex chromosomes and SDM within reptiles, using family-level analyses of character evolution and applying parsimony, likelihood, Bayesian, and stochastic methods. We find support for the common ancestor of amphisbaenians and whiptail lizards (Laterata) possessing the XY (male heterogametic) GSD mechanism, while the ancestors of Testudines and Crocodylia, as well as the larger group Archosauromorpha (here containing turtles) are inferred to have exhibited TSD. We also find evidence consistent with the hypothesis that the XY system is more labile and evolves faster than does the ZW (female heterogametic) system. Phylogenetic-based speciation tests do not support an association between GSD and speciation, and reject the hypothesis that the presence of the XY system is associated with speciation in reptiles.

From the symposium "Reptile Genomics and Evolutionary Genetics" presented at the annual meeting of the Society for Integrative and Comparative Biology, January 2–6, 2008, at San Antonio, Texas.


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