Meeting Abstract

P3.85  Sunday, Jan. 6  Evolution of Rostrum Shape Variation in Mantis Shrimp STEVES, I.D.*; WRIGHT, M.L.; CALDWELL, R.L.; University of California, Berkeley; University of California, Berkeley; University of California, Berkeley isteves@berkeley.edu

Widespread in tropical waters, mantis shrimp rely on their powerful raptorial appendages and keen eyesight to smash or spear their prey. Examined in isolation, the rostrum, a segment of exoskeleton at the base of mantis shrimp eyes, appears to have a singular function: to protect the eye stalk. The rostrum’s large interspecific variation in shape (triangular, trispinous, semi-circular, etc.) suggests that a combination of selection pressures are acting on it. Here, we investigated whether sexual selection facilitated changes in rostrum shape by testing for (1) sexual dimorphism and (2) changes in rostrum proportions associated with sexual maturity. To study the effects of sex and age on the rostrum, we measured rostrum lengths and body sizes of eight species (approximately 40 individuals each) across five superfamilies. An analysis of covariance showed that rostrum lengths differed significantly between males and females in five of the eight species measured. Rostrum proportions in these species generally remained constant across adult body size, but decreased among the Gonodactyloid mantis shrimps. A preliminary examination of these results indicates that the presence or absence of sexual dimorphism may be associated with ecological factors related to habitat, such as space competition and predation style.