A phylogenetic revision of the New Zealand endemic ground beetle genus Oregus Putzeys 1868 (Carabidae : Broscini)

Abstract

The genus Oregus is an endemic broscine ground beetle restricted in distribution to the east coast of the South Island of New Zealand. The taxonomic and phylogenetic relationships within the genus Oregus Putzeys and the abundance and distribution of Oregus inaequalis Castelnau were examined. A cladistic analysis of external morphological and genitalic characters was conducted, as well as genetic analysis using partial cytochrome oxidase I and NADH-dehydrogenase I mitochondrial DNA sequences. A total of 2,196 specimens were examined during the course of this study. Specimens were examined from the entire geographic range of the genus. The cladistic analysis was conducted from 17 populations for the morphological characters and 12 populations for the DNA sequences.

Analysis of morphological characters indicated that male genitalic characters were less homoplasious than external morphology. Parsimony analysis of morphological data separated populations of Oregus into four species; O. aereus White, O. inaequalis Castelnau and two new species, subsequently described as O. septentrionalis n. sp. and O. crypticus n. sp. Mitochondrial DNA sequence data (analysed using parsimony and maximum likelihood) supported the morphological species designations, except for O. crypticus as fresh material for DNA analysis of this species was not available. Genetic diversity between species was between 3.05 and 5.36% across both gene regions. Intraspecific genetic diversity was generally low, except in O. aereus, which had extensive variation between populations (up to 2.48%). The genetic diversity in O. aereus was not reflected in genital morphology.

An extensive pitfall trapping trial failed to collect enough individuals of O. inaequalis at Swampy Summit (Dunedin) to allow accurate estimation of abundance using either mark-removal or mark recapture methods. However, the number of O. inaequalis caught, the low probability of capture and the ratio of O. inaequalis caught to other species of Carabidae would still indicate a relatively large population at Swampy Summit. There was an apparent contraction to the geographical range of O. inaequalis based on the historical literature, which is merely a reflection of several misidentified specimens. Presence/absence pitfall trapping did not extend the historical distribution of O. inaequalis and confirmed that O. inaequalis is a narrow range endemic, restricted to the podocarp broadleaf forests and moist tussock/shrubland ecosystems immediately to the north of Dunedin City. Pitfall trapping did not show any significant contraction to the confirmed range of O. inaequalis.

Oregus. inaequalis, though a distinct taxonomic entity is not regarded as threatened given the lack of range contraction and the apparently substantial population at Swampy Summit. As such it is not recommended as being a candidate for active conservation management.