Meeting Abstract
Bite force is an important measure of performance that directly relates to an organism’s fitness. The forces produced by the jaw muscles limit the types of prey that can be consumed by an individual, and therefore the nutrition and energy available to the individual. Bite forces have been recorded in diverse taxa, yet many interesting examples, such as some profoundly dimorphic species, remain to be studied. We are studying bite performance in map turtles (Graptemys species) that vary dramatically in head size. Map turtles exhibit three different trophic morphologies: The males of all species are considered microcephalic (i.e., have small heads), whereas females may be microcephalic, mesocephalic, or megacephalic (having profoundly large heads). The differences in head size are thought to relate to dietary differences, with megacephalic females being capable of durophagy, and microcephalic individuals being limited to feeding on softer prey items such as aquatic insect larvae. We are measuring bite forces in microcephalic map turtles Graptemys sabinensis and megacephalic ones Graptemys pearlensis. Our preliminary results show that microcephalic individuals generate forces comparable to many turtles that are dietary generalists, whereas megacephalic individuals are capable of producing much higher bite forces, commensurate with those of similarly sized snapping turtles (Chelydra serpentina). These results support the hypothesis that megacephalic map turtles can exploit hard prey that most other species of turtles cannot consume. In future research, we plan to quantify the muscle morphology and maximum tetanic bite forces elicited by direct muscle stimulation.
