Physiological adapation to climate change in larval Colias butterflies

Background/Question/Methods

Understanding how local adaptation affects a population’s ability to adapt to novel thermal regimes is increasingly important given recent climate change. Colias butterflies have served as a model system for thermal adaptation for over 50 years, these butterflies range from lowland to alpine habitats across North America. Due to climate change, increased temperatures causing extended growing seasons are mainly affecting larval growth and development. We study the thermal performance curves (TPCs) of larval feeding rate for four populations of Colias eurytheme and Colias eriphyle in North America that occur over a broad range of elevations and climates. We measured their physiological adaptation to temperature by quantifying thermal performance curves (TPCs) of short-term feeding rate. Do these four populations of C. eriphyle and C. eurytheme have differences in their TPCs in regards to feeding rate? Are these differences in feeding rate due to differences in their local and seasonal environmental temperatures?  In addition, we compare our data on TPCs for two of these populations, C. eurytheme from the Sacramento Valley, CA and C. eriphyle from the Montrose Valley, CO, with historical data collected in 1971. Are there differences in TPCs for feeding rates in these populations over the past 40 years, and do those differences correspond to how climate has changed in these areas?

Results/Conclusions

Populations at lower elevations with longer growing seasons had broader TPCs for larval feeding rate. In contrast, higher elevation populations with shorter growing seasons had higher optimal and maximal temperatures for feeding. As a result, populations at higher elevations were largely restricted to feeding during daytime within the growth season, whereas populations at lower elevations could potentially feed during both daytime and nighttime conditions. Using historical data for two of the populations, we assessed changes in both climatic (T_air) conditions and TPCs for larval feeding.  Overall mean air temperatures during the growing season showed little change at the two sites, but the frequency of high air temperatures (>28°C) has increased markedly at both sites over the past 40 years.  This climatic shift was associated with increased rates of larval feeding at higher temperatures (>28°C) in both populations. These results suggest that recent climate warming has led to physiological shifts in the TPCs for larval feeding in this system, implicating larval thermal adaptation as an important response that may ameliorate the fitness consequences of rapid climate change in insects.