The Mecyclothorax beetles (Coleoptera, Carabidae, Moriomorphini) of West Maui, Hawaii: taxonomy, biogeography, and conservation

Abstract

Species of the genus Mecyclothorax Sharp are taxonomically revised for West Maui, resulting in recognition of 27 species, 23 newly described: M. allostriatus, M. arcanus, M. badius, M. bartletti, M. ceteratus, M. clermontiae, M. curtimutinus, M. excavatus, M. exilioides, M. ferovipennis, M. filitarsis, M. geminatus, M. improcerus, M. kahalawaiae, M. lyratus, M. minimops, M. oppenheimeri, M. pallidus, M. platops, M. scapulatus, M. ustulatus, M. vicinus, and M. vulcanoides. Among the species are two pairs of cryptic sibling species best diagnosed by male and female genitalia. In the sibling species pair M. lyratus and M. arcanus, the former species is geographically restricted to Hanaula, an isolated southern massif in West Maui, whereas the latter is distributed on the main massif, Puu Kukui. Mecyclothorax scapulatus is also restricted to Hanaula supporting recognition of this massif as a distinct area of endemism within the Mauna Kahalawai mountain system. Species comprising a second sibling species pair, M. allostriatus and M. geminatus, exhibit a mosaic geographic distribution wherein each locality supports only one species, but the species distributions interdigitate among the various isolated localities from which the two species are known suggesting a more complicated speciation history. The genus Mecyclothorax is treated as part of an austral assemblage of genera classified as the tribe Moriomorphini (stat. n.). Species richness and endemism are compared among West Maui carabid beetles, land snails (Gastropoda), and Drosophilidae (Diptera). Carabid beetles with 46 species present in West Maui are less rich than the land snail fauna of 59 species and drosophilid fly fauna of 51 species. Over all genera, carabid beetles exhibit 87% species-level endemism to West Maui, with Mecyclothorax species 100% precinctive. Percentage endemism across all snail groups is somewhat lower – 73% – but among the more diverse snail families Achatinellidae and Amastridae, fraction endemism is similar to beetles, being 80% and 88% respectively. Drosophilidae exhibit much lower levels of endemism, with only 25% of West Maui species restricted to the volcano. Authochthonous speciation occurs at similar rates in all three groups, with species duration in all three groups estimated to be 0.2–0.3 Myr. The higher fraction endemism in beetles versus flies can be explained in part by absence of metathoracic flight wings in 48 of the 51 resident carabid species versus the retention of flight by the flies. Mecyclothorax species diversity peaks at 1200–1300 m elevation. This elevational zone supports closed canopy forest with a well-developed forest floor leaf litter microhabitat, enabling occupation by subarboreal trunk and moss inhabitants as well as terrestrial litter-inhabiting taxa. Mecyclothorax species are recorded in habitats ranging from 600m to the highest West Maui summit at 1760 m elevation. Their present-day persistence in this broad range of natural habitats makes them suitable subjects for habitat monitoring and continued biotic survey. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)