Biogeography of The New Zealand Subantarctic Islands: Phylogenetics of Pseudhelops (Coleoptera: Tenebrionidae)

Abstract

Pseudhelops (Titaeini, Tenebrionidae) is distributed on all New Zealand subantarctic islands, and the more northern Chatham and Stewart Islands. The species are saprophagous and feed mainly on rotten wood or lichen. The taxonomic limits of the species of Pseudhelops are re-evaluated in the context of a cladistic study of nine terminal taxa (11 characters from larvae and adults rooted with Cerodolus) and a population genetics study of the Auckland Island species P. tuberculatus. Based on the mitochondrial cytochrome c oxidase subunit I (COI) gene (Auckland island species rooted with P. posticalis) and morphological assessment of larval and adult characters, P. wenhami is removed from synonymy with P. tuberculatus and reinstated as a valid species. Pseudhelops wenhami is present mainly at higher altitudes on Auckland islands, while P. tuberculatus is found at lower altitudes. Pseudhelops tuberculatus COI haplotype clades were poorly-supported but displayed a clear isolation-by-distance pattern with geographically proximate populations possessing identical or closely related haplotypes. All of the haplotypes observed from the southernmost, pristine and predator-free Adams Island were also shared with Auckland Island. Twenty-six trees produced in the cladistic analysis showed the following island relationships in the consensus tree: Snares + Chatham (Stewart (Antipodes, Auckland, Campbell, Auckland (Bounty + Antipodes))). The biogeographic pattern suggests that island populations more distant from the mainland are more derived and that P. antipodensis represents either a recent coloniser from west Campbell Plateau, or is a remnant from a previously widespread ancestor. A polytomy for most of the species furthest from the mainland could be the result of recent and simultaneous speciation, though the lack of phylogenetic resolution could also be the result of a soft polytomy. Phylogenetic placements, presence of two Pseudhelops species on the Antipodes Islands and the isolated species, Pseudhelops liberalis and P. clandestinus on the eastern Bounty Platform may be in conflict with geological dates derived from volcanics for Antipodes Islands and suggest the presence of sunken islands, or at least older dates for the Bounty Platform. Sympatry on two islands, as in the case of Pseudhelops, is not unusual for beetles. There are at least 15 other occurrences of co-existence on the subantarctic islands. Some of the morphological synapomorphies that unite P. liberalis and P. clandestinus may be related to feeding in rocky habitats that lack herbaceous or woody vegetation.