Residual yolk energetics and postnatal shell growth in Smooth Softshell Turtles, Apalone mutica

We examined functions of residual yolk (RY) in hatchling Smooth Softshell Turtles (Apalone mutica). Removal of RY did not affect survival, shell growth, or resting metabolic rates of turtles for 40 d after hatching. Our estimates of metabolic rate suggest that RY can fuel maintenance and activity metabolism for approximately 25 days. A. mutica absorb more than 1g of water in the first 2 weeks of life, which appears to be the basis of post-hatch shell expansion rather than yolk-provisioned growth. Post-hatch growth may be limited by the magnitude of RY remaining at hatching, but RY protein and lipid proportions do not differ from those of freshly-laid eggs. In addition, A. mutica did not use RY to fuel nest emergence. Our results suggest that RY does not fulfill several hypothetical functions in A. mutica, including postnatal growth, catabolic fuel for nest emergence, and long-term nutritional sustenance for maintenance, activity, or hibernation. Instead, A. mutica appear to absorb most yolk prior to hatching, and are left with a minimum of RY. Variation in RY mass with incubation regime in other species suggests that mothers may overprovision their eggs to ensure successful development across a diversity of possible incubation conditions.