Mating asymmetry and the direction of evolution in the Hawaiian cricket genus Laupala

Based on studies from native Hawaiian Drosophila, a model was proposed to e xplain sexual isolation and mating asymmetry, from which one could potentia lly infer the 'direction of evolution'. We examined sexual isolation betwee n allopatric cricket species of the genus Laupala, another endemic Hawaiian insect with an elaborate mating system, to begin to explore the nature of sexual isolation and mating asymmetry in closely related Hawaiian organisms . We studied sexual isolation and mating asymmetry in two contrasts. First, an inter-island comparison, including L. makaio from the older island of M aul and L. paranigra from the younger island of Hawaii, and second, an intr a-island (Hawaii) comparison, including L. nigra from the older volcano of Mauna Kea and L. paranigra with a primary distribution on the younger volca noes of Mauna Loa and Kilauea. We used a 'no-choice' experimental design, p airing individual males and females in homospecific or heterospecific combi nations. Several behavioural aspects of courtship (proportion of male singi ng, latency to male singing, production of spermatophores and courtship ini tiation speed) were quantified as well as the success or failure of matings . We demonstrate asymmetry in sexual isolation between reciprocal combinati ons of L. makaio and L. paranigra. This result is examined in light of the differences in courtship behaviour manifest in the experiments with these t wo species. We did not find evidence of asymmetry in sexual isolation betwe en L. nigra and L. paranigra, although differences in courtship initiation speed were evident between reciprocal combinations of these two species. In addition to the geological argument that species on older islands and olde r volcanoes give rise to species on younger islands and younger volcanoes, we discuss phylogenetic evidence consistent with these biogeographic hypoth eses of relationships among the focal taxa. The patterns of asymmetrical se xual isolation and mating asymmetry are consistent with those found in the native Hawaiian Drosophila.