Evol Ecol Res 3: 953-967 (2001) Full PDF if your library subscribes.
Environmental effects on fitness and consequences for sex allocation in a reptile with environmental sex determination
Steven Freedberg,* Michael A. Ewert and Craig E. Nelson
Department of Biology, Indiana University, Bloomington, IN 47405, USA
Although populations of most sexual species exhibit a 1 : 1 sex ratio, biased ratios are often associated with environmental sex determination. Theoretical models predict that species with environmental sex determination will bias sex allocation in favour of the sex produced in the environment that yields lower fitness. These models have been proposed as an explanation for the biased sex ratios observed in many reptiles with environmental sex determination. We explore the effects of developmental environment on sex allocation in Graptemys ouachitensis, a turtle with environmental sex determination. We found that developmental environments producing males were poorest for survival, growth and performance, suggesting that the sex ratio of G. ouachitensis should be male-biased. This expectation contrasts with the observed female bias in G. ouachitensis. Warmer than average temperatures may have contributed to the female-biased hatchling sex ratios reported for G. ouachitensis in some studies. However, the strongly skewed population sex ratios in map turtles indicate female-biased allocation. The frequent finding of female-biased primary sex ratios in many species indicates an overall trend of female-biased sex allocation in reptiles with environmental sex determination. The conflict between this tendency for female biases and our results suggests that environmental effects on fitness will not explain the general tendency to skewed sex ratios. The apparent incongruency between our findings and theoretical models concerning sex allocation and environmental sex determination suggests that an alternative model that focuses on nest-site inheritance might explain better the female-biased sex ratios observed for G. ouachitensis and other reptiles with environmental sex determination.
Keywords: Chelydra serpentina, Graptemys ouachitensis, nest-site inheritance, sex ratio, temperature-dependent sex determination.
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