Impacts of climate driven range changes on the genetics and morphology of butterflies

This thesis studied the genetic responses of butterflies to climate induced distribution shifts in terms of patterns of genetic diversity at expanding and contracting range margins, the relative importance of genes versus environment on adaptations to dispersal and local adaptation to temperature during range expansion.

Loss of genetic diversity during range expansion in Pararge aegeria was confirmed using neutral genetic markers (AFLPs). High reductions of genetic diversity were discovered at the range margin relative to the distribution core. Range margin populations exhibit a nearly 50% reduction in neutral genetic diversity, and lower genetic divergence between sites.

The contracting southern range margin of the butterfly Erebia aethiops has not suffered a reduction in genetic diversity relative to the distribution core. As genetic diversity remains relatively high population extinction is unlikely to be exacerbated by inbreeding or reduced fitness from low genetic diversity during range contraction.
Contrary to results from laboratory reared butterflies, wild male P. aegeria do not have significant differences in flight morphology between core and margin sites. This suggests developmental influences suppress the expression of genetic adaptations to dispersal. Wild butterflies also represent a smaller range of phenotypes possibly indicating balancing selection on morphological traits.

Little to no evidence for local adaptation to temperature is apparent at the expanding range margin of P. aegeria. Neither was there evidence for reduced fitness due to lower genetic diversity, as F2 butterflies from core sites had poorer survival rates than the less genetically diverse margin sites.

This study found that neutral genetic diversity is unlikely to affect species during distribution shifts as even high losses during distribution expansion do not appear to affect survival rates. Also adaptation to dispersal and temperature may be limited during range expansion both by environmental constraints and limited selection pressure respectively.