Complex effects of day and night temperature fluctuations on thermally plastic traits in an experimental model of adaptive seasonal plasticity.

Abstract

BackgroundChanges in development in response to seasonally variable environments can produce phenotypes adjusted to fluctuating seasonal conditions and help organisms cope with temporal heterogeneity. In contrast to what happens in natural situations, experimental studies of developmental plasticity typically use environmental factors held constant during development, precluding assessment of potential environment-by-environment interaction effects.\n\nResultsWe tested effects of circadian fluctuations in temperature on a series of thermally plastic traits in a model of adaptive seasonal plasticity, the butterfly Bicyclus anynana. Comparing phenotypes from individuals reared under two types of fluctuations (warmer days with cooler nights, and cooler days with warmer nights) and those reared under a constant temperature of the same daily average allowed us to identify complex patterns of response to day and night temperatures. We found evidence of additive-like effects (for body size), but also different types of \"dominance\"-type effects where one particular period of the light cycle (for development time) or one particular extreme temperature (for eyespot size) had a relatively larger contribution to phenotype expression. We also gathered evidence against the hypothesis that thermal plasticity in development time drives thermal plasticity in other traits.\n\nConclusionsCombined effects of fluctuating day and night temperatures include additive-like effects as well as different types of environmental-dominance interaction effects. Differences between plastic traits reveal independent responses to temperature, and possible independent assessment of temperature conditions. Our study underscores the importance of understanding how organisms integrate complex environmental information towards a complete understanding of natural phenotypic variation and of the potential impact of environmental change thereon.