The Influence of Fluctuating Countervailing Selection in Maintaining within Population Variation in Sexually Selected Traits

Arizona State University, Scottsdale AZ

Investigators

Abstract

Abstract: Susan Bertram 0131728 This research addresses how heritable variation may be maintained within a population. Research on heritable variation is important because it has implications for biodiversity: extinction removes species, speciation adds them; and heritable variation is the fodder for speciation. While data suggests that genetic variation in traits that enhance fitness is quite common, current theory predicts almost no heritable variation in fitness conferring traits. This inconsistency between theory and data reveals the importance of determining the underlying mechanisms responsible for maintaining heritable variation. The goal of this research is to investigate how heritable variation may be maintained in sexually selected traits by directly testing the hypothesis that heritable variation in mating signals can be maintained by temporally fluctuating and opposing forces of sexual and natural selection. The Texas field cricket, Gryllus texensis, is an ideal system to test this hypothesis as male crickets display extensive mating signal variation, all signaling components measured to date exhibit high heritabilities, and signals are easily measured. Further, female crickets discriminate between potential mates based on mating signals, and signaling males are often attacked and killed by acoustically orienting parasitoids. Crickets have two breeding seasons, spring and fall. In the spring cricket and parasitoid densities are low, in the fall they are high. Density influences the intensity of selection, because in the low-density spring populations female crickets discriminate between mates with different songs. In the high-density fall populations selection appears reversed, with female crickets selecting mates randomly and signaling males being targeted by parasitoids. To test whether temporally fluctuating natural versus sexual selection can maintain variation, my research will first confirm that the mating signals are heritable. Selection experiments will then determine how natural and sexual selection influence variation in calling behavior over several generations. The proposed research will be the first experimental test of the hypothesis that conflicting selection forces shape mating signal variation within a population.