Hold on for One more Day: Oviductal egg retention as a mechanism for flexible reproductive phenology in Eastern Musk Turtles (Sternotherus odoratus)

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In oviparous reptiles, parental care is often limited to the energy allocated to embryos prior to oviposition. Energy used by reproducing females is allocated towards, nutrient acquisition, fertilization, vitellogenesis, determining the number and size of eggs, eggshell calcification, oviductal egg retention (retaining eggs within the oviduct after fertilization), and nesting activities. Oviductal egg retention in turtles ranges from two weeks to half a year and permits flexibility in the timing of oviposition and is a pivotal mechanism in determining reproductive phenology. The energetic cost of oviductal egg retention in Eastern Musk Turtles (Sternotherus odoratus) was investigated by measuring the metabolism of females prior to and following oviposition. Gravid female metabolic rates were adjusted by subtracting clutch metabolic rates and were elevated relative to males and non-gravid females, indicating an associated energetic cost for egg retention. The metabolism of gravid females was relatively constant across the period of oviductal egg retention, but 40% higher pre-oviposition than post-oviposition. Metabolic costs associated with egg retention were correlated with clutch mass and female body mass, but not with clutch size or number of days leading up to oviposition. These results suggest the strategy of oviductal egg retention, has considerable energetic costs for Eastern Musk Turtles, but likely provides critical flexibility in nesting phenology.