Complex multi-trait responses to multivariate environmental cues in a seasonal butterfly

Developmental plasticity in a seasonal environment allows an organism to optimally match its life-history traits with the fluctuating conditions. This critically relies on abiotic and biotic factors, such as temperature or food quality, that act as environmental cues and predict seasonal transitions. In most seasonal environments, multiple factors vary together, making it crucial to understand their combined effects on an organisms phenotype. Here, we study plasticity in a multivariate environment in the butterfly Bicyclus anynana that exhibits two distinct seasonal phenotypes. Temperature is an important cue mediating plasticity in this species, but other environmental cues such as larval host plant quality could also be informative since plant quality deteriorates during the transition from wet to dry season in the field. We examine how temperature and host plant quality interact to affect life-history traits. Using a full-factorial design, we expose cohorts of larvae to either poor (old plants) or high (young plants) quality plants at different temperatures. Our results show that plant quality had a temperature and sex-dependent effect on life-history traits. At lower and intermediate temperatures, it decreased body mass and prolonged development time, indicating that poor plant quality acted as a stressor. However, metabolic rates in adults were not affected, indicating that individuals could, at least in part, compensate for stressful juvenile conditions. In contrast, at higher temperatures poor plant quality induced a partial dry-season phenotype, indicating that it may have acted as an environmental cue. Moreover, poor plant quality, particularly in males, also decreased the correlation between life history traits, signifying disrupted phenotypic integration. Our study reveals complex interactive effects of two environmental variables on seasonal plasticity, reflecting differences in their reliability as seasonal cues. This highlights the importance of studying the combined effects of multiple environmental factors to better understand the regulation of phenotypic plasticity in wild.