Environmental sex determination
Environmental sex determination or ESD is any sex-determination system in which sex is established by a nongenetic cue (e.g. nutrient availability) experienced within a discrete period after conception. In contrast, genotypic sex determination (GSD) occurs when sex is established by genetic factors (e.g. sex chromosomes) at conception. Environmental sex determination should also not be confused with some forms of hermaphroditism in which the sex is determined flexibly after birth, such as dichogamy.
In the season in the amphipod Gammarus duebeni, photoperiod induces production of males earlier, and females later. Because male fitness improves more than female fitness with increased size, environmental sex determination is adaptive in this system by permitting males to experience a longer growing season than females. The adaptive significance of environmental sex determination is not so clear for amniotes, however, the clade in which this it is perhaps most common.
Most amniote vertebrates have genetic sex determination, but a small highly diverse set of taxa in this clade show environmental sex determination. In these latter animals, environmental sex determination occurs as temperature-dependent sex determination (TSD), wherein sex of individuals is permanently determined by thermal conditions experienced approximately during the middle one-third of embryonic development. Mammals and birds only have genetic sex determination, whereas crocodilians and sphenodontians exclusively have temperature-dependent sex determination. In contrast, squamates (lizards and snakes) and turtles exhibit both genotypic sex determination and temperature-dependent sex determination, although the latter is much more common in turtles than in squamates.
- F. J. Janzen & P. C. Phillips (2006). "Exploring the evolution of environmental sex determination, especially in reptiles" (PDF). Journal of Evolutionary Biology 19 (6): 1775–1784. doi:10.1111/j.1420-9101.2006.01138.x. PMID 17040374.
- J. McCabe & A. M. Dunn (1997). "Adaptive significance of environmental sex determination in an amphipod". Journal of Evolutionary Biology 10 (4): 515–527. doi:10.1046/j.1420-9101.1997.10040515.x.
- Fredric J. Janzen & Gary L. Paukstis (1991). "Environmental sex determination in reptiles: ecology, evolution, and experimental design". Quarterly Review of Biology 66 (2): 149–179. JSTOR 2830229. PMID 1891591.
- Nicole Valenzuela & Valentine A. Lance, ed. (2004). Temperature Dependent Sex Determination in Vertebrates. Smithsonian Institution. ISBN 978-1-58834-203-4.
- James J. Bull (1983). Evolution of Sex Determining Mechanisms. Menlo Park, California: Benjamin Cummings. ISBN 978-0-201-11242-9.
- Fredric J. Janzen & James G. Krenz (2004). "Phylogenetics: which was first, TSD or GSD?" (PDF). In Nicole Valenzuela & Valentine A. Lance. Temperature Dependent Sex Determination in Vertebrates. Smithsonian Institution. pp. 121–130. ISBN 978-1-58834-203-4.
- Yasuhiko Kato, Kaoru Kobayashi, Hajime Watanabe, Taisen Iguchi (2011). "Environmental Sex Determination in the Branchiopod Crustacean Daphnia magna: Deep Conservation of a Doublesex Gene in the Sex-Determining Pathway". PLoS Genetics 7 (3): 1–12. PMID 21455482.