Meeting Abstract
Increased jaw loading during feeding induces a strong hypertrophic response in jaw bones and adductor muscles in mammals, but such plasticity has not been investigated in reptiles. The American alligator (Alligator mississippiensis) is an opportunistic predator, capable of swallowing small items with minimal oral processing, as well as tearing large prey apart in a violent death roll. The latter behaviour exerts large forces on the crocodilian jaw apparatus, which may alter its cranial growth trajectory. We studied whether death-roll training can induce a plastic response in skull shape and bite-force performance in juvenile (400-2500 g) female alligators (n=32 per group). For eight months, experimental animals fed by performing death rolls on chicken drumsticks twice a week, while control animals were fed small chunks of chicken meat. Following training, unilateral bite forces were measured in triplicate, and the jaw out-lever for each trial determined from a video recordings. Body mass and head size had a significant effect on the maximum bite torque, but death roll did not. There was no significant difference of feeding mode on relative cranial shape (head width:length, snout:braincase length). The correlation coefficient of standardised bite force on body mass was greater in experimental animals (0.76) than controls (0.38), suggesting that muscle activation is more finely tuned in animals exposed to unyielding prey items. Overall, the alligator skull does not exhibit bone plasticity in response to long-term exposure to high feeding forces. We propose that bone plasticity is not observed in crocodilians, given their sit-and-wait predatory strategy. Whether apparent lack of musculoskeletal plasticity is ancestral for archosaurs, or derived in crocodilians, is yet to be determined.
