Biogeography and Evolution of New Zealand Priasilphidae (Coleoptera: Cucujoidea)

Abstract

The phylogenetic relationships of the seven species of the endemic New Zealand genus Priasilpha were reconstructed by a cladistic analysis of 22 adult characters. One fully resolved tree was produced that was rooted with the Tasmanian species Priastichus megathorax with the following relationships among Priasilpha (distributions in square brackets): (P. aucklandicus [Auckland Island] + P. obscura [South Island and southern North Island]) (P. angulata [Franz Joseph Glacier, Westland] (P. earlyi [Kellys Creek, Arthurs Pass] (P. carinata [Mt. Arthur, Northwest Nelson] (P. bufonia [Richmond Range, Northwest Nelson, Marlborough] + P. embersoni [Paparoa Range, Buller Region])))). The only winged species, P. obscura, is placed as a sister taxon to P. aucklandicus, both of which are in a basal clade that is a sister group to the remaining species. Aptery evolved early in the genus and there is a statistically significant morphological trend towards body roundness, with basal species elongate in shape and derived species progressively more rounded. The P. angulata clade is found to the west of the Alpine Fault and is part of the Challenger Plateau, a cratonic fragment forming the southernmost limit of the Melanesian Rift. Priasilpha obscura is found mainly on Torlesse and Waipapa terranes and is of east Gondwanan origin. Priasilpha aucklandicus is restricted to the Campbell Plateau, a cratonic fragment derived from west Gondwana. The phylogeny of Priasilpha suggests that the Melanesian Rift-Torlesse split occurred prior to the East-West Gondwanan split (hypothesis 1), which is clearly contradicted by their relative ages. If the flighted P. obscura is deleted from consideration or if it is assumed that it was once a Campbell Plateau species, then this older distribution supports a hypothesis that there is a basal East-West Gondwanan split occurring about 100 Ma. If, however, P. aucklandicus evolved from a P. obscura + P. aucklandicus ancestor some time after 20 Ma, then the derived east-west Gondwanan split is falsified and the distributions are an artefact due to faunal mixing (hypothesis 2). Examination of a 3-taxon statement for the genera of Priasilphidae (Chileosilpha [Southern Chile] (Priastichus [Tasmania] + Priasilpha [New Zealand])) supports hypothesis 2 where the East-West Gondwana split preceded one between East Gondwana and the Melanesian Rift.