A Biogeographical Analysis of the Tasmanian Endemic Ptunarra Brown Butterfly, Oreixenica ptunarra Couchman (Lepidoptera : Nymphalidae : Satyrinae)

Abstract

Considerable geographic variation occurs in the Tasmanian endemic butterfly, Oreixenica ptunarra, and there is a high correlation between clusters of morphological characters and ecological factors, especially climate and elevation. Evidence is presented for the existence of a longitudinal cline in phenotypic characters of wing pattern and size, which is unrelated to the modest amount of variation in the male genitalia (a possible surrogate for genetic variability). Butterflies from warmer, less cloudy eastern Tasmania are larger and less dark in colour than those from the west, culminating in the small dark populations of the north-west. This suggests selection for efficiency in thermoregulation as climatic conditions become more marginal for adult activity from east to west. The prevailing subspecies classification does not fully reflect the range of variation in this species. Conservation strategies that aim to guarantee the survival of the collective phenotype of O. ptunarra based on this taxonomy are therefore misinformed. The north-west populations are disjunct geographically and in features of phenotype, but are not especially discrete in the morphology of the male genitalia. We propose that the subspecies angeli Couchman and roonina Couchman be reduced to synonymy with nominotypical ptunarra Couchman, and a new subspecies should be recognised to incorporate populations from the montane grasslands of north-western Tasmania.