Temperature dependent sex determination: Evaluation and hypotheses

Publisher Summary This chapter discusses the concept of temperature dependent sex determination (TSD). TSD is most frequently observed in species that lack heteromorphic sex chromosomes. The phenomenon of TSD was first recorded by Charnier in 1966 when he observed that the lizard, Agama agama , had a skewed sex ratio, which was dependent upon the temperature of egg incubation. The phenomenon of TSD has been shown to exist in the wild and in laboratories; the studies of the American alligator have shown that the sex ratio in the wild is approximately five females to every male. For animals with TSD, sex is not determined at conception, but rather some time during embryonic development by the temperature of egg incubation. A single sex is commonly seen to develop at extreme temperatures, with a mixture of sexes developing at intermediate temperatures. TSD is the predominant sex determining mechanism in turtles; the only documented occurrence of sex chromosomes is one of male heterogamety in the mud turtle, family Kinosternidae. The chapter also reviews the problems associated with TSD.