Growth, developmental and stress responses of larvae of the clouded sulphur butterfly Colias eriphyle to repeated exposure to high, sub-lethal temperatures

The optimal temperature at which an organism grows and develops is commonly correlated with latitude and elevation; however, the maximum temperature for physiological performance often is not. This makes performance at temperatures between the optimum and themaximum of particular interest. Temperature can influence long-term performance (growth and development), as well as short-term performance (heat shock protein) responses differentially. In the present study, two populations of the clouded sulphur butterfly Colias eriphyle Edwards that differ in elevation, thermal regime and optimal and maximum temperatures are studied to quantify their responses to repeated, sub-lethal heat treatments early in development (second instar). Heat treatments accelerate development during the second to fourth instars in both populations initially, although this effect disappears by pupation. Heat treatment decreases pupal mass in the lower elevation population, suggesting that repeated exposure to high temperatures early in developmentmay reduce final size and fecundity in this population. Heat shock protein gene (hsp70) expression levels in the lower elevation (1633m a.s.l.) population are highest 24 h after the start of the heat treatment and then the fall to pre-exposure levels by 36–72 h, suggesting a rapid response to stressful temperatures. By contrast, heat treatment has no significant effect on pupal mass in the higher elevation (2347m a.s.l.) population. This population has higher levels of hsp70 expression overall but constant expression levels, suggesting that the temperature treatments used are insufficient to elicit a heat stress response. Overall, the effects of repeated exposure to sub-lethal high temperatures early in development on growth, final size and gene expression differ between populations that differ in thermal sensitivity.