PHYSIOLOGICAL-RESPONSES TO CARBON-DIOXIDE IN EMBRYONIC RED-EARED SLIDER TURTLES, TRACHEMYS-SCRIPTA

In the red-eared slider turtle, Trachemys scripta, sex is determined by the incubation temperature of the egg: warm temperatures produce females, cool ones produce males, and a narrow range of intermediate temperatures produce both sexes. We asked whether the influence of temperature is modified by the effects of carbon dioxide. Under one current hypothesis, sex is more closely linked to total incubation time than to temperature. Higher levels of carbon dioxide should lengthen total incubation time and thus mimic the longer incubation times produced by low incubation temperatures. By this hypothesis longer incubation times should increase the tendency to produce males. Trachemys scripta eggs were incubated in atmospheres containing various concentrations of carbon dioxide. While total incubation times were significantly lengthened with elevated carbon dioxide (as if mimicking cool temperatures), sex ratios were altered in favor of females (as if mimicking warm temperatures). This result is compatible with a hypothesis that pH changes affect sex in turtles with TSD. Turtles incubated at elevated levels of carbon dioxide absorbed less yolk, had more residual yolk, and were somewhat smaller than turtles incubated at lower levels of carbon dioxide. In some cases, clutches were heterogeneous in their responses to the various levels of carbon dioxide.