Reptiles are a fascinating group for the study of sexual development because they exhibit a wide range of sex-determining mechanisms, from strict genetic sex determination (GSD) to strict thermal sex determination (TSD) and intermediate systems of GSD that are to various degrees overridden by environmental effects . This thematic issue presents the latest data on different aspects of sex determination in reptiles. Following an evolutionary perspective on why reptiles might be predisposed to evolve TSD, the papers in this issue explore in detail the different genetic and molecular mechanisms of sex determination and differentiation. They consider recent findings such as the discovery of new genes differentially expressed at male and female sex-determining temperatures, a new model of the role of aromatase, and the contribution of heat-shock proteins to TSD in the American alligator. Further studies examine the role played by sex allocation, the advantage of viviparity, and the effects of anthropogenic climate change on the sex ratio in TSD reptile populations. Providing a valuable overview for both students and researchers, this publication is essential reading for developmental and reproductive biologists, herpetologists, comparative endocrinologists, evolutionary biologists and geneticists.

Edited by the world's foremost authorities on the subject, with essays by leading scholars in the field, this work shows how the sex of reptiles and many fish is determined not by the chromosomes they inherit but by the temperature at which incubation takes place.

This book is the first to report that research in allogenics/xenogenics has conclusively shown that fishes have retained bisexual potency even after sexual maturity and spermiation. The XY genotype found in the unexpected female phenotypes sired by supermales (Y1Y2) and androgenic males (Y2Y2) points out the need to employ sex specific molecular ma

Many reptiles exhibit temperature-dependent sex determination (TSD), a sex-determining mechanism in which the incubation environment permanently determines offspring sex. This research had two main objectives: (1) to evaluate the roles of two traits (nesting behavior by females and offspring sex ratios in response to thermal incubation conditions) thought to be important for maintaining sex ratios in this system, using the painted turtle (Chrysemys picta), and (2) evaluate the adaptive significance of TSD in a genotypic sex determining system (GSD). Observations on the nesting behavior of painted turtles suggest that either females in this population do not use soil surface temperature as a cue for selecting nest sites, or select sites with intermediate soil surface temperatures that may be less likely to bias sex ratios. Geographic comparisons from two populations of C. picta inhabiting differing climates (Illinois and New Mexico) demonstrated that the New Mexico population exhibited a significantly higher pivotal temperature (temperature producing a 1:1 sex ratio) than the Illinois population. However, this difference was small compared to differences in climatic conditions experienced by the populations. Chrysemys picta nests from Illinois and New Mexico experienced similar nest temperatures despite a relatively hot year in New Mexico. Nests in New Mexico were not laid in sites most likely to reduce nest temperatures, but instead at sites experiencing high soil moisture, which indirectly reduced nest temperatures. In simulation models, pivotal temperatures evolved more rapidly than did nest-site choice by females in response to perturbed sex ratios. Natal philopatry to nest sites also caused maladaptive nesting behavior in terms of Fisherian sex ratio selection. Simulation models demonstrated that TSD invades populations exhibiting GSD and reaches fixation through several avenues that do not include a widely accepted adaptive function for TSD (the Charnov-Bull model). Results from these studies suggest that the likelihood of TSD being relatively neutral compared to GSD in reptiles deserves more attention. Consequently, selection for female behavior and offspring thermal sensitivity to adaptively adjust sex ratios may be fairly weak. This conclusion is supported by the small observed differences in pivotal temperatures and lack of strong patterns of thermally-based nest-site selection.