Life history consequences of miniaturization in turtles: evidence from the subfamily Kinosterninae (Testudines: Kinosternidae)

A miniaturized species is one that has endured ecological, physiological or life history costs due to small size and has implemented discrete strategies to compensate for those costs. We studied the impact of small size on the reproductive biology of the miniaturized turtle, Sternotherus minor (Kinosternidae: Kinosterninae), by exploring two alternative hypotheses that explain within-clutch trade-offs: the Optimal Egg Size Theory (OEST) and the Morphological Constraint Hypothesis (MCH). Female S. minor in this study showed a combination of reproductive parameters that support both the MCH and the OEST. Small individuals follow the MCH and larger individuals follow the OEST, fitting the previously proposed 'threshold size-constrained' model of egg size to female size. The large proportion of suboptimally-sized eggs (31.1%) produced in our study population is evidence that a novel strategy that compensates for very small size exists in this kinosternine turtle. Early reproduction in our study population, as well as a mobile plastron made up of a reduced number of bones and scutes in all members of this subfamily, is strong evidence of paedomorphosis, a frequent consequence of miniaturization. Re-examination of reproduction in other kinosternines will further test how this life history strategy facilitated miniaturization in testudines.