Meeting Abstract

S8-2.3  Jan. 6  Acceleration and power output in gravid green iguanas SCALES, J.A.*; BUTLER, M.A.; Univ. of Hawaii, Manoa; Univ. of Hawaii, Manoa jscales@hawaii.edu

A major selective pressure for the evolution of sexual dimorphism is differential reproductive roles of the sexes (Darwin, 1871). Females of many species experience large increases in mass and volume related to bearing a reproductive load. Carrying a reproductive load presumably encumbers locomotion, yet females must retain locomotor performance essential for predator escape and daily activities. Therefore, selection to maintain locomotor performance while gravid may lead to sexual dimorphism in morphology or performance abilities. In particular, acceleration is an ecologically important aspect of locomotor performance which should particularly be affected by reproductive load. We investigated the ability of female iguanas to produce force and power during accelerations while gravid. We found that gravid iguanas can accelerate at a similar rate to recovered “normal” iguanas by producing extremely high power (up to 1560 W/kg) for a given acceleration. The increase in power is not due to increases in peak forces, but high force production during an extended step duration. The high power outputs suggest that accelerations in gravid iguanas may be power limited, but the similarity in acceleration between gravid and recovered iguanas reveals that non-gravid iguanas have excess performance capacities. These results provide insight on the selective pressures or biomechanical constraints that may result in dimorphisms related to maintaining performance while gravid. I will discuss how these biomechanical findings may relate to other aspects of reproductive ecology.