Meeting Abstract

P1.19  Thursday, Jan. 3  Bateman Gradients and Alternative Mating Strategies SAUNDERS, Katharine M.*; SHUSTER, Stephen M. ; The University of Texas at Austin; Northern Arizona University k.saunders@mail.utexas.edu

Among the available methods for estimating the intensity of sexual selection, the Bateman gradient is considered one of the most accurate, because it specifically measures the standardized covariance between mate numbers and offspring numbers for members of each sex. Although widely used to compare sex differences in selection intensity, it has yet to be used to examine the covariance between mate numbers and offspring numbers among alternative mating strategies. We allowed marine isopods (Paracerceis sculpta) representing the 3 genetically distinct male morphs in this species to mate from 1 to 5 times, and we allowed females to mate 1, 3 and 5 times. We compared the total number of offspring produced by each mating or sequence of matings using 2-way ANOVA. We found that females gained no additional fitness from mating with multiple males, whereas male fitness increased with increasing mate numbers. There were no significant differences in the Bateman gradients for α-, β- and γ-males, and no significant differences in the fitnesses of α-, β- and γ-males allowed to mate with 1-5 females in succession. In nature, the fitnesses of the 3 morphs are highly variable, apparently due to differences in the availability of receptive females. Our results suggest that differences in mate availability, not differences in sexual competence, are responsible for observed variance in fitness within, and for the equality of fitnesses among, the 3 male morphs in this species.