Abstract

The 15 species of Mecyclothorax Sharp precinctive to New Caledonia are revised and shown by cladistic analysis to comprise a monophyletic lineage, here treated as subgenus Phacothorax Jeannel. The New Caledonian species of subgenus Phacothorax include Mecyclothoraxfleutiauxi (Jeannel), M.najtae Deuve, and 13 newly described species: M.jeanneli sp. n., M.laterobustus sp. n., M.laterorectus sp. n., M.laterosinuatus sp. n., M.laterovatulus sp. n., M.manautei sp. n., M.megalovatulus sp. n., M.octavius sp. n., M.paniensis sp. n., M.picdupinsensis sp. n., M.plurisetosus sp. n., and two jointly authored species; M.kanak Moore & Liebherr sp. n., and M.mouensis Moore & Liebherr sp. n.. subgenus Phacothorax is one of five subgenera recognized within genus Mecyclothorax based on cladistic analysis of 65 exemplar taxa utilizing information from 137 morphological characters. The four other monophyletic subgenera include the precinctive Australian Eucyclothorax subgen. n. (type species Mecyclothoraxblackburni [Sloane]), the precinctive Queensland Qecyclothorax subgen. n. (type species Mecyclothoraxstoreyi Moore), the precinctive New Zealand Meonochilus Liebherr & Marris status n., and the geographically widespread and very diverse nominate subgenus, distributed from St. Paul and Amsterdam Islands, eastward across Australia and New Guinea, and in the Sundas, Timor Leste, Lord Howe and Norfolk Islands, New Zealand, and the Society and Hawaiian Islands. The biogeographic history of Mecyclothorax can be derived from the parsimony cladogram time-calibrated by times of origin of particular geographic areas inhabited by resident representative species. Based on sister-group status of subgenus Phacothorax and subgenus Mecyclothorax, and occupation of Lord Howe Island–an island originating no earlier than 6 Ma–by the earliest divergent lineage within subgenus Mecyclothorax, the ancestor of present-day Phacothorax spp. is hypothesized to have colonized New Caledonia 6 Ma, subsequent both to Cretaceous Gondwanan vicariance as well as any Oligocene submergence. Area relationships among the New Caledonian Phacothorax point to earliest diversification incorporating the northern massifs, and most recent diversification on the ultramafic volcanic substrates in the south of Grand Terre. Flight wing loss has played an important role in shaping the various island faunas, both in their morphology as well as their diversity. The retention of flight capability in only a few of the many hundred Mecyclothorax spp. is presented in light of how populations evolve from macropterous colonizing propagules to vestigially winged specialists. Interspecific differences in genitalic structures for the sister-species pair M.fleutiauxi + M.jeanneli are shown to involve functional complementarity of male and female structures. Extensive geographic variation of male genitalia is demonstrated for several New Caledonian Mecyclothorax spp. This variation deviates from the geographically uniform male genitalia exhibited by species in the hyperdiverse Mecyclothorax radiation of Haleakalā volcano, Maui, suggesting that extensive sympatry occurring among species in that diverse species swarm selects for stability within this mate recognition system. Conversely, lower levels of sympatry characterizing the depauperate New Caledonian radiation permit the presence of more extensive male genitalic variation, this variation not selected against due to the lower likelihood of interspecific mating mistakes.

Highlights

  • The carabid beetle fauna of New Caledonia comprises elements ranging from the mundane to the bizarre

  • Though the New Caledonian N. kanak is precinctive to the island, and is the product of speciation within New Caledonia, its presence on the island can tell us little about the history of New Caledonia

  • Abacophrastus Will, an endemic New Caledonian genus of pterostichine Carabidae with seven precinctive New Caledonian species (Will 2011), is a candidate for implicating events of earth history based on the phylogenetic relationships both within and external to the genus

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Summary

Introduction

The carabid beetle fauna of New Caledonia comprises elements ranging from the mundane to the bizarre. Of much more interest both morphologically and potentially biogeographically are those lineages that have radiated in New Caledonia resulting in numerous native, precinctive species. Such biological diversity may belie longer periods of residency by these lineages offering the possibility that earlier geological events influenced their phylogenetic history. Immense disparity across an island radiation may evolve adaptively in isolated and restricted island situations over a very short time, such as with Mecyclothorax carabid beetles of the Society and Hawaiian Islands (Liebherr 2013, 2015) Characterizing such biological diversity is the first step toward hypothesizing the context within which a particular lineage has evolved. Can biogeographic hypotheses be proposed and tested using area-based methods such as vicariance biogeography (Nelson and Platnick 1981, Ladiges and Cantrill 2007), or temporal-calibration methods such as lineage divergence dating based on molecular sequence data (Grandcolas et al 2008, Nattier et al 2017)

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