Carbon dioxide influences environmental sex determination in two species of turtles

Eggs of wild caught Trachemys scripta and Graptemys pseudogeographica kohnii , two emydine turtles known to have temperature-dependent sex determination, were incubated at 28.5°C in boxes aerated with one of four gas mixtures (two in G. p. kohnii ). Across all eggs, elevated levels of carbon dioxide significantly feminized sex ratios in both species and also reduced hatching success. When eggs were grouped into clutches, all comparisons between 0% and elevated carbon dioxide showed feminization in the portions of the clutches at elevated carbon dioxide, a statistically significant result for T. scripta. Accumulation of biogenic carbon dioxide from embryonic respiration and other sources is thus likely to affect sex ratios in natural nests under some conditions, perhaps through an effect on some aspects of embryonic pH.