An analysis of skeletal size variation in Mystacina robusta Dwyer, 1962 (Chiroptera: Mystacinidae)

Size variation within the presumably extinct greater short-tailed bat Mystacina robusta is described from a variety of teeth and longbone measurements. Data from recent specimens collected from Big South Cape and Solomon Islands are compared with those from fossil bones, mainly of Holocene age, from the Waitomo - Hawkes Bay and Martinborough regions of the North Island, and Takaka, North Canterbury and South Canterbury in the South Island, New Zealand. Variation is clinal, with size decreasing significantly southwards. The hypothesis is proposed that this clinal variation is a net response to two selection pressures. Firstly, it was advantageous for M. robusta to be relatively large to exploit the abundant macro-invertebrates and microvertebrates available on the forest floor. Secondly, large size would have been increasingly cold-limited towards the south, where the energy required to rewarm the animals from the near-ambient temperatures reached during torpor was greatest.