Sexual dimorphism and alternative reproductive tactics in the Midland Painted Turtle (Chrysemys(picta(marginata)

Abstract

The reproductive strategy of Painted Turtles (Chrysemys picta) has been described as a combination of male courtship and female mate choice. However, in situ field observations from a long-term study of C. picta in Algonquin Provincial Park (Ontario, Canada) suggest that males also demonstrate coercive mating tactics. Males are equipped with prominent tomiodonts, tooth-like cusps of the upper jaw, which seemingly function in restraining mates and result in wounding to the head and neck of females. I propose that the tomiodonts of male C. picta serve as sexual weapons used to coerce females into mating. This thesis has two main objectives: 1) to describe the tomiodont morphology of C. picta, and 2) to test the functional significance of tomiodonts in the mating tactics of male C. picta. In Chapter I, I investigate the overall cranial morphology of C. picta with an emphasis on sexual dimorphism of the tomiodonts. I show that male C. picta have sexually size dimorphic tomiodonts with an optimized arrangement for biting and gripping. In Chapter II, I investigate the soft tissue wounding demographics of a C. picta population as these wounds relate to antagonistic sexual interactions. Using a 24-year dataset on wounding I show that large females experience the highest wounding probability and that elevated rates of wounding occur during the late summer breeding period. In Chapter III, I use behavioural trials during the spring and late summer reproductive seasons to evaluate male reproductive behaviour. I show that small males court females through titillation, whereas larger males employ coercive tactics, such as biting and forced submergence. My findings are contrary to the female choice mating system reported for C. picta and join a growing body of research demonstrating the importance of coercive tactics in the reproduction of male emydid turtles.