Sperm Utilization Patterns and Reproductive Success in Captive Loggerhead Turtles (Caretta caretta)

We investigated the effects of the order of sequential matings in captive female loggerhead turtles (Caretta caretta) on the paternity of their successive clutches. Paternity analysis revealed that only 3 of the 7 successive clutches were multiply sired, although all egg-laying females were observed to copulate with multiple males prior to egg-laying. In multiply sired, successive clutches of particular females, the relative paternal contributions of different males did not vary, although some potentially successful matings were observed during internesting intervals. Prior to nesting periods, males showed mating in response to the female reproductive cycle in which the cumulative durations of mountings observed by highly sensitive cameras peaked at 21-40 days before any individual female laid her first clutch. A regression line between cumulative duration of mountings and relative parental contributions for 21-40 days before laying the first clutch fit a predictive equation for sperm competition based on the assumptions of a fair raffle. These results suggest that sperm precedence has changed with time over the course of a prenesting period and that male turtles in this study have regulated the timing of copulations in accordance with the patterns of sperm precedence.