Incubation temperature effects on hatchling growth and metabolic rate in the African spurred tortoise, Geochelone sulcata


We tested competing hypotheses regarding the persistence of temperature-dependent sex determination (TSD) in the African spurred tortoise (Geochelone sulcata (Miller, 1779)), by measuring the effects of incubation temperature (Tinc) on a suite of physiological and behavioral endpoints, including resting metabolic rate, yolk-to-tissue conversion efficiency, posthatching growth, and temperature preference. Correlations of these variables with Tinc could lend support to the hypothesis that TSD persists owing to sex-specific benefits of development at specific temperatures, whereas absence of Tinc effects support the null hypothesis that TSD persists simply because selection favoring alternate sex determining mechanisms is weak or absent. The metabolic rate Q10 value exhibited temporal variation and was higher immediately after hatching compared with 40 or 100 days posthatching, and mass conversion efficiency varied among clutches. Incubation temperature correlated inversely with duration of embryonic development, but did not influence yolk conversion efficiency, growth, or resting metabolic rate. Thus, our results provide little evidence indicating contemporary benefits of TSD, suggesting that TSD in G. sulcata is no longer evolutionarily adaptive but persists because selection against it and in favor of other sex-determining mechanisms is weak, or that TSD is an adaptive trait but for reasons not elucidated by this study.

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Canadian Journal of Zoology