Presentation on theme: "Chelydra serpentina and possible origins of TSD Alexandra Eckart Biology Department Eastern Ct. State University."— Presentation transcript:
Chelydra serpentina and possible origins of TSD Alexandra Eckart Biology Department Eastern Ct. State University
Experimental evidence for the evolutionary significance of temperature-dependent sex determination. Evolution (1995) 49: 864-873 Frederic J. Janzen
Charnov and Bull (1977) pioneers in research: GSD- ESD sex determination –TSD- temperature sex determination TSD considered to be favored by natural selection. They proved that incubation temperature influenced offspring gender. Certain temperature ranges also improved overall fitness for females and males.
Experiments 26ºC produced all male hatchlings. 28ºC produced a mix of both male and female hatchlings. 30ºC produced only female hatchlings.
Frederic Janzen: Incubation temperature and behavioral responses Evolutionary adaptations –TSD- temperature sex determination as an evolved antipredator mechanism.
Life history Snapping turtles live > 50 yrs. Reach sexual maturation by the 19 th yr. High fecundity (up to 83 eggs /clutch). Most perish during the first year of life. Wide range of habitat.
Study : National Wildlife Refuge (Illinois). Eggs were collected from five fresh nest sites and divided into groups of twenty. Eggs were rehydrated weekly in vermiculate to provide a constant hydric environment. Hatchlings were incubated at preset temperatures of 26, 28 and 30ºC producing three experimental groups of all males, all females and mixed hatchlings.
Sex determined by direct examination of gonadal morphology, (Otoscopic procedure). Released into experimental pond in Nov. 1 st,1995 and recollected the following May. Measurement of carapace, mass, plastron length and the logs of swimming and running speed, the square roots of both propensities to run and swim (Cubic spline Analysis).
Survivorship The percent of survival was greatest for incubation of male hatchlings at 26ºC and 30ºC for females.
Early behavior and survivorship correlation: predator avoidance Less motility during 1 st year of development showed greater degree of survivability. snapping turtles have plastrons that enable greater leg movement for walking on the bottom of ponds or streams.
Summary The higher the temperature the more likely female offspring will be produced. Cooler temperatures produce significantly more male offspring. Hatchlings incubated at 28ºC had higher tendencies to run and therefore experienced greater rates of mortality.
Offspring from the cooler incubation temperatures swam faster than those incubated in the warmer temperatures, this data however was not used. The more motionless a turtle remains during the first year of development the greater chances of survival, due to substrate camouflaging. Environmental impacts: Global warming
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