Hold on for One More Day: Energetic Costs of Oviductal Egg Retention in Eastern Musk Turtles (Sternotherus odoratus)

In oviparous reptiles, parental care is often limited to the energy allocated to embryos before oviposition. Reproducing females can allocate energy toward vitellogenesis, determining the number and size of eggs, fertilization, eggshell calcification, retention of eggs within the oviduct after fertilization (oviductal egg retention), and nesting activities. Oviductal egg retention in turtles ranges from 2 wk to half a year, permitting flexibility in the timing of oviposition. The energetic cost of oviductal egg retention in eastern musk turtles (Sternotherus odoratus) was investigated by measuring the metabolism of females before and after oviposition. Gravid female metabolic rates were elevated relative to male and nongravid female metabolic rates, indicating an associated energetic cost for egg retention. Metabolism of gravid females was 40% higher before oviposition than after oviposition, and it was relatively constant across the period of oviductal egg retention. Metabolic costs associated with egg retention were correlated with clutch mass and female body mass but not with clutch size or the number of days leading up to oviposition. These results suggest that the strategy of oviductal egg retention has considerable energetic costs for eastern musk turtles but that it likely provides critical flexibility in nesting phenology.