BackgroundDevelopmental plasticity is thought to have profound macro-evolutionary effects, for example, by increasing the probability of establishment in new environments and subsequent divergence into independently evolving lineages. In contrast to plasticity optimized for individual traits, phenotypic integration, which enables a concerted response of plastic traits to environmental variability, may affect the rate of local adaptation by constraining independent responses of traits to selection. Using a comparative framework, this study explores the evolution of reaction norms for a variety of life history and morphological traits across five related species of mycalesine butterflies from the Old World tropics.ResultsOur data indicate that an integrated response of a suite of key traits is shared amongst these species. Interestingly, the traits that make up the functional suite are all known to be regulated by ecdysteroid signalling in Bicyclus anynana, one of the species included in this study, suggesting the same underlying hormonal regulator may be conserved within this group of polyphenic butterflies. We also detect developmental thresholds for the expression of alternative morphs.ConclusionsThe phenotypic plasticity of a broad suite of morphological and life history traits is integrated and shared among species from three geographically independent lineages of mycalesine butterflies, despite considerable periods of independent evolution and exposure to disparate environments. At the same time, we have detected examples of evolutionary change where independent traits show different patterns of reaction norms. We argue that the expression of more robust phenotypes may occur by shifting developmental thresholds beyond the boundaries of the typical environmental variation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-0907-1) contains supplementary material, which is available to authorized users.

We would like to thank Andrew Balmer for help with the plant measurements, and the Radiating Butterflies Group for helpful discussions. This study was

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 organism’s 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.