Allocation of Reproductive Output: Egg- and Clutch-Size Variation in the Diamondback Terrapin

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A fundamental component of an organism's life history is the allocation of energy available for reproduction into units that will simultaneously produce successful offspring and maximize the lifetime reproductive success of the female. We present five years of data on egg- and clutch-size variation for a single population of the diamondback terrapin, Malaclemys terrapin. Clutch size ranged from 4-22 eggs and correlated weakly with female plastron length. Mean egg mass ranged from 6-12 g among clutches. Egg mass did not correlate with female plastron length and female postparturition mass. Consistent with optimal egg size theory, we observed that clutch size varied more than egg size when we considered population averages. However, egg mass correlated negatively with clutch size only during one year. Thus, there was no persistent trade-off between clutch size and egg size. On the other hand, consistent with developmental plasticity, we observed that clutch size and egg size varied simultaneously among clutches of individual females. Thus, neither optimal egg size theory nor developmental plasticity provided an informative explanation for the egg-size variation we observed in terrapins.