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.

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.

Reptiles have been a topic for scientific study for many decades and remain widely studied around the world. In particular, their reproductive patterns and strategies have been extensively studied, proving useful in analysis of life-history strategies. A pivotal aspect of reptilian reproduction is incubation of eggs. Oviparity is found in all turtles, crocodilians and the tuatara and is prevalent in many lizards and snakes. Many aspects of the eggs, embryos and incubation conditions have been the subject of numerous scientific reports. This volume is dedicated to systematic analysis of reptilian incubation. The concept for the book is to look at reptilian eggs, development and incubation conditions in a functional way with particular emphasis on the natural incubation environment and, rather than concentrating on Family accounts, (e.g. incubation in crocodilians) the chapters review the topics in all reptile types allowing for the first time a systematic comparison of incubation between crocodilians, turtles and squamates. In addition to reviewing current information, the authors briefly look towards the future and outline areas where further research is needed.

Sexual reproduction is a fundamental aspect of life. It is defined by the occurrence of meiosis and the fusion of two gametes of different sexes or mating types. Sex-determination mechanisms are responsible for the sexual fate and development of sexual characteristics in an organism, be it a unicellular alga, a plant, or an animal. In many cases, sex determination is genetic: males and females have different alleles or different genes that specify their sexual morphology. In animals, this is often accompanied by chromosomal differences. In other cases, sex may be determined by environmental (e.g. temperature) or social variables (e.g. the size of an organism relative to other members of its population). Surprisingly, sex-determination mechanisms are not evolutionarily conserved but are bewilderingly diverse and appear to have had rapid turnover rates during evolution. Evolutionary biologists continue to seek a solution to this conundrum. What drives the surprising dynamics of such a fundamental process that always leads to the same outcome: two sex types, male and female? The answer is complex but the ongoing genomic revolution has already greatly increased our knowledge of sex-determination systems and sex chromosomes in recent years. This novel book presents and synthesizes our current understanding, and clearly shows that sex-determination evolution will remain a dynamic field of future research. The Evolution of Sex Determination is an advanced, research level text suitable for graduate students and researchers in genetics, developmental biology, and evolution.