Parnassius smintheus overwintering project
Parnassius smintheus is a high altitude butterfly which lives in the Rockies (US and Canada). The caterpillars feed on the leaves of the succulent Sedum lanceolata, and the adults feed on its nectar. Over the last 20 years, there has been dramatic variation in population growth from year to year, yet it seems that the drops in population correspond to years with excessively warm Novembers. The general hypothesis is that the warm Novembers affect the larvae's ability to survive the winter. The aim of the project is to determine the exact way in which warm Novembers affect the mechanisms of overwintering.
Understanding the mechanisms which these butterflies use to survive the winter is essential for their conservation (this is the primary focus of my collaborators in the Matter lab). Yet this project also has implications for insect thermobiology more generally. As the climate is rapidly changing, it is important to understand the ways in which overwintering conditions affect survival and population processes in different insects, in order to be able to predict and manage insect populations in the (near) future (this is the primary focus of my collaborators in the Sinclair lab).
We have collected P. smintheus eggs from the field site in Kananaskis AB (in 2015 and 2016). They incubated incubate in realistic ecological conditions (variable night and day temperatures, variable humidity) until November. Then, the eggs were divided into two groups: the control will incubate at standard (cool) November temperatures while the experimental group incubated in a warm treatment. After that, all the eggs continued incubating at realistic ecological conditions, simulating winter and spring temperatures, until they hatch. We have conducted a number of parallel experiments on the two different groups, including:
- Measurement of energy reserves
- Measurement of Supercooling Points
- Survivorship after hatching
- Energy Reserves: TBD (early 2018)
- Supercooling points: There was no effect of early-winter environment on supercooling points. Overall, the supercooling points were much lower than normal winter temperatures in the field.
- Survivorship after hatching (starvation resistance): There was no effect in starvation tolerance after hatching between the two experimental groups. This suggests that early-winter conditions do not substantially drain energy stores, but we will also test energy reserves directly (lipid content, carbohydrates and protein).
Next Steps (will be conducted by Kurtis Turnbull, Sinclair lab)
- Freezing & lack of hardening: measure mortality after long-term (chronic) cold exposure (above the supercooling points). As the supercooling points were much lower than what the larvae experience in the field (beneath snow cover), the issue could be that that warmer early-winter conditions affect the ability of the eggs to harden, making them more susceptible to freezing.
- Premature emergence: If larvae from the warm treatment emerge prematurely, they could then experience cold-related energy depletion or mortality.
- Energy Reserves: Additional experiments to be conducted.
I am indebted to the Sinclair lab (Western University) and the Matter lab (University of Cincinnati) for introducing me to these ideas, helping me out and for putting up with and engaging with an interminable number of philosophical questions. After leaving Western for Helsinki, the experimental work is being continued by Kurtis Turnbull (Western University, Sinclair lab).