D3412: Analyzing thermal performance of butterflies across a broad latitudinal range to predict responses to climate change

Insects whose ranges occupy broad latitudinal or elevation gradients must be physiologically capable of persisting across a broad range of climates. This may be accomplished via a single, highly plastic physiology, by local genetic or epigenetic adaptation, or a combination of these mechanisms. As ectotherms, it is well known that insect development is highly dependent on temperature. However, the mechanisms used by single species of butterflies - or other insects that persist across large latitudinal ranges - with broadly different temperature regimes is not well understood. Here, we investigated the growth rates from two populations of silvery blue (Glaucopsyche lygdamus) and Western white (Pontia occidentalis) butterflies, both of which have ranges that reach from the Arctic Ocean to Southern California. We hypothesized that thermal performance is locally adapted within butterfly species. If this is true, we predict that larvae from California will have higher survival rates, growth rates, and body mass at pupation in the warmest treatments and and high mortality in the coldest treatments. In contrast, larvae from Alaska will be most successful in the coldest treatments with high mortality in the warmest treatments. To test this we are conducting growth trials at four temperatures (16C, 21C, 26C, and 30C) on wild caught G.lygdamus andP. occidentalis from Fairbanks, Alaska and Davis, California. Preliminary analyses indicate that populations from both regions have similar temperature-growth responses, but Alaskan larvae in the warmest treatments exhibited lower survivorship indicating a potential trade-off between survivorship and development time.