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EXPERIMENTAL EVIDENCE FOR THE EVOLUTIONARY SIGNIFICANCE OF TEMPERATURE‐DEPENDENT SEX DETERMINATION
Author(s) -
Janzen Fredric J.
Publication year - 1995
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.1995.tb02322.x
Subject(s) - hatchling , chelydra , biology , incubation , turtle (robot) , survivorship curve , zoology , ecology , hatching , biochemistry , genetics , cancer
The evolutionary significance of sex‐determining mechanisms, particularly temperature‐dependent sex determination (TSD) in reptiles, has remained unresolved despite extensive theoretical work. To investigate the evolutionary significance of this unusual sex‐determining mechanism, I incubated eggs of the common snapping turtle ( Chelydra serpentina ) at a male‐producing temperature (26°C), a female‐producing temperature (30°C), and an intermediate temperature that produced both sexes about equally (28°C). Laboratory experiments indicated that two performance variables, but no morphological measurements, were significantly influenced by incubation temperature ( P ≤ 0.05): hatchlings from cooler incubation treatments swam faster than turtles from warmer incubation treatments, and hatchlings from 28°C exhibited a greater propensity to run than did individuals from 26°C and 30°C. In the field, hatchlings from the all‐male and all‐female producing temperatures had significantly higher first‐year survivorship than did consexuals from the incubation temperature that produced both sexes ( G = 6.622, P = 0.03). Significant directional selection was detected on propensity of hatchlings to run (β′ = –0.758, P = 0.05): turtles that tended to remain immobile had a higher probability of first‐year survivorship than did individuals that moved readily. Thus, the effects of the gender × incubation temperature interaction on survivorship of hatchling turtles observed in the field experiment may have been mediated by temperature‐dependent antipredator behavior. These results provide a possible functional explanation for the evolutionary significance of TSD in turtles that is consistent with predictions of theoretical models.