Wing pattern morphometrics: genetic adaptation of an Australian butterfly to global warming

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Life Sciences, College of Science, Health and Engineering, La Trobe University, Bundoora.

Global surface temperature has increased over the past 30 years and both rainfall and humidity have spatially and temporally altered. The models often used to predict species distributional responses to climate change, do not consider that organisms can genetically adapt to change. Methods of predicting species’ responses must take this into account. In the 1970s Pearse and Murray investigated geographic variation in genetically determined wing-characters of both female and male Common Brown butterflies (Heteronympha merope). In females, geographic variation in wing phenotypes was found to have climatic associations. Given the magnitude of recent climatic changes I hypothesise that H. merope will have correspondingly responded via genetic adaptation, which will be evident in wing morphological characters. In this study I have analysed geographic variation in contemporary H. merope populations using the previously studied characters. Associations of female wing phenotypic characters with the moisture-related climatic variables rainfall and humidity have been found. Some male wing characters are associated with minimum temperature. It is argued that these associations reflect sex-specific consequences of thermoregulatory biology. Consistent patterns of association exist in both the Australian south-eastern mainland subspecies H. m. merope and in Tasmanian populations (H. m. salazar). Comparisons of contemporary populations with Pearse’s data and with Museum specimens reveal temporal changes in wing characters some of which are associated with population-specific changes in climatic variables over the thirty year period. The results of this study, taken together with recent genetical and ecophysiological studies of H. merope, indicate that this species has been able to adapt genetically to shifts in climate that have occurred in south-eastern Australia since the 1970s. This is an important outcome for understanding implications of climate change, and the extent to which this may apply to other species is also considered.