The Role of Sexual Selection on Speciation in Two Firefly Species: Photinus ardens and Photinus carolinus

Bole, Gregory

The objective of this dissertation is to better understand the role of sexual selection in speciation events. I have investigated the variation present in the male flash patterns used by females to identify and locate potential mates in two closely related species of fireflies (Coleoptera: Lampyridae): Photinus ardens and Photinus carolinus. I studied the preferences females have to a full range of flash signals ranging from below the population's lower limit to above the highest boundary of natural variation in order to find out what sort of potential sexual selection is imposed by female choice. A DNA phylogeny. including each species in the ardens species group and some more distantly related fireflies, suggests Photinus carolinus and the third member of the species group, Photinis consimilis, are sister species and Photinus ardens is the sister species to the clade they form. By comparing the direction of differences in flash characters between these three species and the direction that selection pressures from female choice are pushing them I tested the hypothesis that sexual selection has operated on male courtship traits creating differences that have caused or enhanced speciation. The results of this study match a number of the predictions that support my hypothesis. Three of the elements of the courtship signals in the species studied, flash length, flash interval, and flash number, have the potential to act as isolating mechanisms between P. ardens and P. carolinus or P. consimilis. These isolating mechanisms have been shown to be the primary characteristics preventing the genetic mixing of these species. Each of the characteristics acting as an isolating mechanism was demonstrated to be under directional sexual selection due to female choice. One of the three characters, flash number, shows divergent sexual selection between P. ardens and P. carolinus, demonstrating the strongest support for the hypothesis that sexual selection caused the isolation of these species.