Understanding the mechanisms and evolutionary processes that lead to reproductive isolation between populations is the major goal of speciation research. Here, I integrated approaches from phylogenetics, population genetics, and behavioral ecology to gain perspective on a behavioral isolating mechanism between two species of Chihuahuan desert katydids. Previously little was known about the genus Obolopteryx described over 100 years ago. In the first chapter I built the first molecular phylogeny from two mitochondrial DNA genes and compared my hypothesis to previous morphology-based hypotheses. In the second chapter I used Amplified Fragment Length Polymorphisms (AFLP) to compare total genetic similarity of allopatric and sympatric populations of the two focal species: O. oreoeca and O. brevihastata. I found substantial evidence that O. oreoeca was experiencing a gene-flow restriction between the allopatric population in the Chisos Mountains of the Big Bend National Park and the population in the Davis Mountains sympatric with O. brevihastata. I did not find equivalent support for differentiation between the two O. brevihastata populations. In the third chapter I explored the calling behavior of the males in both species, and the phonotactic responses of O. oreoeca females between allopatry and sympatry. I quantitatively described the calls of both species. I then tested whether various aspects of calls differed in allopatry and sympatry within each species. I tested for character displacement in call syllable durations of both species. I found that O. oreoeca populations showed no differences in most call features, but they did show character displacement in the syllable duration. Interestingly, while I failed to find character displacement in O. brevihastata's syllable duration, I found that other unexpected call features differ between their populations. Controlled experiments show that a high amplitude component of the male call is important for female O. oreoeca phonotaxis. Sympatric O. oreoeca females showed significantly decreased phonotactic responses to heterospecific calls compared to allopatric O. oreoeca females. This combined molecular and behavior data suggest a unique example of reinforcement in which females in a peripheral sky island population, sympatric with a non-sister species, have evolved strong heterospecific mating discrimination due to heterospecific competition for mates.Zoolog
