Environmental sex determination
Environmental sex determination is the establishment of sex by a non-genetic cue, such as nutrient availability, experienced within a discrete period after conception. This is in contrast to genotypic sex determination, which establishes sex at conception by genetic factors such as sex chromosomes. Environmental sex determination is different to some forms of sequential hermaphroditism in which the sex is determined flexibly after birth.
The amphipod crustacean Gammarus duebeni produces males early in the mating season, and females later, in response to the length of daylight, the photoperiod. 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 branchiopod crustacean Daphnia magna parthenogenetically produces male progeny in response to a combination of three environmental factors, namely a reduced photoperiod in autumn, shortage of food and raised population density.
The sex of most amniote vertebrates, such as mammals and birds, is determined genetically. However, some reptiles have temperature-dependent sex determination, where sex is permanently determined by thermal conditions experienced during the middle third of embryonic development. The sex of crocodilians and sphenodontians is exclusively determined by temperature. In contrast, squamates (lizards and snakes) and turtles exhibit both genotypic sex determination and temperature-dependent sex determination, although temperature dependence is much more common in turtles than in squamates.
- Janzen, Fredric J.; Phillips, P. C. (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.
- McCabe, J.; Dunn, A. M. (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.
- Kato, Yasuhiko; Kobayashi, Kaoru; Watanabe, Hajime; Iguchi, Taisen (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. doi:10.1371/journal.pgen.1001345. PMC 3063754. PMID 21455482.
- Gilbert, Scott (2006). Developmental biology (8th ed.). Sunderland, Mass.: Sinauer Associates. p. 552. ISBN 9780878932504.
- James J. Bull (1983). Evolution of Sex Determining Mechanisms. Menlo Park, California: Benjamin Cummings. ISBN 978-0-201-11242-9.
- 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. doi:10.1086/417143. JSTOR 2830229. PMID 1891591.
- Nicole Valenzuela; Valentine A. Lance, eds. (2004). Temperature Dependent Sex Determination in Vertebrates. Smithsonian Institution. ISBN 978-1-58834-203-4.
- Janzen, Fredric J.; Krenz, James G. (2004). "Phylogenetics: which was first, TSD or GSD?". In Nicole Valenzuela; Valentine A. Lance (eds.). Temperature Dependent Sex Determination in Vertebrates (PDF). Smithsonian Institution. pp. 121–130. ISBN 978-1-58834-203-4.