Genetic responses to climate change in the common brown butterfly (Heteronympha merope)

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

Climate change is occurring rapidly and has already been shown to affect species in a variety of ways such as shifts in species distribution and abundance as well as changes to phenology. Species responses’ to climate change will depend on many factors including the ability to genetically adapt and with very little literature providing direct evidence for genetic adaptation to climate change across a species range, further research is needed to understand the potential of a species to do so. In this thesis a model species, the Common Brown butterfly Heteronympha merope has been used to study the temporal and spatial changes in potentially adaptive genes (allozyme loci previously shown to have an adaptive role in other butterfly species) in relation to recorded changes in maximum and minimum temperature, rainfall and humidity. Heteronympha merope provides a baseline for this work as past research by Pearse (1978) provides historical allozyme allele frequencies for three loci (Aat, Gpi and Pgm) in populations across the entire range. These have been compared to contemporary allele frequencies. Loci with no known adaptive association, including nuclear DNA markers, were included to provide a potential scale of neutral divergence in the contemporary analyses. In contemporary populations, there is evidence of drift, locally adaptive selection and balancing selection. The majority of loci show an association with site characteristics (either spatial or environmental or both). Temporally, changes in allozyme allele frequencies across the species range were associated with changes in maximum temperature (Gpi), minimum temperature (Pgm), rainfall and humidity (Aat). Significant variation over time was more likely in isolated populations, suggesting fewer constraints on evolution in these populations. These results provide evidence for the potential for genetic adaptation to occur over a relatively short time period (30 years or generations) at a species level.