Meeting Abstract

52.1  Sunday, Jan. 5 10:00  Does Size Really Matter? The Effect of Genital Size on Reproductive Success DREYER, AP*; SHINGLETON, AW; Michigan State University; Michigan State University dreyerau@gmail.com

From flies to spiders and crabs to beetles, genital size remains near constant among individuals in a population despite considerable phenotypic plasticity in body size and the size of other organs. Several competing hypotheses have been proposed to explain the selective pressures underlying this commonly observed phenomenon, however, a lack of experimental data has made it difficult to distinguish between them. Any comprehensive test of these hypotheses requires high levels of variation in genital size alone, which does not exist in natural populations. We have designed a method to circumvent this problem and test the hypotheses experimentally. Our design uses targeted gene expression to up- or down-regulate insulin-signaling in the developing genitalia of Drosophila melanogaster and produce male flies with extreme genital morphologies. Male flies with proportionally small, wild-type or large genitalia are then paired with female flies in up to three contexts; (1) no male competition, (2) direct male-male competition, (3) indirect male-male competition. Specific aspects of male reproductive success are measured to compare across the three genital sizes: courtship and copulation latency, and duration; post-mating egg production, proportion of fertilized eggs and egg paternity. Our results suggest that females prefer males with wild-type size genitalia even though they are physically able to mate with, and fertilize eggs using sperm from, males that have proportionally small or large genitalia.