Levels of neutral mitochondrial (mt)DNA sequence diversity play a prominent role in alpha taxonomy, with divergence thresholds of approximately 3% widely being accepted as indicative of species differences. However, a number of studies of New Zealand invertebrates conclude that intraspecific mtDNA divergences are commonly much higher. We investigated the diversity and distribution of mitochondrial cytochrome oxidase I DNA sequences from populations of the New Zealand ground weta Hemiandrus pallitarsis with respect to variation among ten morphological characters and analysis of acoustic signalling associated with mate recognition. We looked for correlation between neutral mtDNA sequence variation and potential indicators of species differences. Despite high genetic distances (> 8.0% uncorrected) among mtDNA haplotypes in this species, morphological and male precopulation signals refute a hypothesis that multiple species exist. Other possible explanations for high genetic diversity, including accidental sampling of nuclear paralogues and elevated substitution rate, are not supported, whereas there is evidence for stable population size through time. We conclude that generalizations about genetic diversity and species status are overly simplistic. In some circumstances, notably southern hemisphere invertebrate taxa, species cohesion appears to have been retained throughout the Pleistocene, indicating the persistence of a relatively high population size.

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Species' ranges along altitudinal clines are probably influenced by their ability to adapt to a range of abiotic factors. Physical adaptations in response to lower temperatures at higher altitudes often include changes in body size. We investigated the distribution and potential change in body size with altitude of two species of ground wētā, Hemiandrus maculifrons and Hemiandrus pallitarsis in the Moehau Ecological Area on the Coromandel Peninsula, North Island, New Zealand. Over eight nights of searching, 17 adult H. maculifrons and 28 adult H. pallitarsis were found. Hemiandrus maculifrons was the smaller of the two species and was found at higher altitudes compared with H. pallitarsis (91-577 m and 27-207 m, respectively). No ground wētā were caught in baited and unbaited live-catch pitfall traps (40 set at 211-242 m above sea level; 40 at 620-626 m above sea level). Despite what appeared to be a tendency for the size of male H. maculifrons to increase with altitude, we found no evidence of intraspecific variation in body size with altitude although sample sizes were small. Nevertheless, these two species of ground wētā appear well suited to further investigations into aspects associated with factors that influence body size, distributional range shifts and climate change.