PRE-MATING COMMUNICATION AND HYBRIDIZATION BETWEEN TWO MEADOW KATYDIDS, ORCHELIMUM NIGRIPES AND O. PULCHELLUM (ORTHOPTERA: TETTIGONIIDAE): MALE CALLING SONG AND ASYMMETRIC FEMALE PREFERENCE

Abstract

I investigated the role of male calling song and female preference on mate choice and pre-mating isolation in Orchelimum nigripes and O. pulchellum. In Chapter 1, I show that the calls of O. nigripes and O. pulchellum differ significantly in multiple temporal characteristics. Given that male signals are different, I next determined whether or not there was species discrimination by females in caged mating trials. In chapter 2, I show female O. nigripes mated preferentially with O. nigripes while O. pulchellum females mated with both O. nigripes and O. pulchellum males. To isolate the acoustic preference of females for male song from other signals and exchanges, I tested female song preference on a walking compensator (a "servosphere") with playback of male song. In chapter 3, I demonstrate that female preference in both species is more complex than a simple preference for increased call energy, and that females of both species will orient to male songs of either species. Katydids from within the hybrid zone were characterized in two ways, song (Chapter 1) and mitochondrial DNA (mtDNA, Chapter 2). Songs from hybrid populations collected within the zone differed in temporal patterning from songs of allopatric Orchelimum nigripes and O. pulchellum, and were less variable than songs of allopatrics. Individuals collected across the hybrid zone primarily carried O. pulchellum mtDNA. This is consistent with the hypothesis that the southeastern hybrid zone was formed by crosses between O. pulchellum females and O. nigripes males, and is also consistent with the results of the caged mating trials in Chapter 2.