Adaptation of a tropical butterfly to a temperate climate

Abstract

Developmental plasticity enables organisms to cope with environmental heterogeneity, such as seasonal variation in climatic conditions, and is thought to affect a species’ capability to adapt to environments with novel seasonal and ecological dynamics. We studied developmental plasticity of the widespread tropical butterfly, Bicyclus safitza, which reaches the southern edge of its distribution in the temperate zone of South Africa. In wet–dry seasonal environments in tropical Africa, adults of Bicyclus butterflies are present all year round and exhibit discrete seasonal forms in alternating generations. We demonstrate that a population that colonized a more temperate climate region has adopted a different strategy to cope with the local environment. No active adults were encountered during the temperate winter. The flight season coincided with a period when evaporation stress was lowest and temperatures were higher in the South African population. Butterflies collected from the field did not express seasonal polyphenism or show full expression of the tropical wet season form phenotype. Reaction norm experiments comparing stocks from South Africa and Uganda indicated that local adaptation of this tropical butterfly to a more temperate climate involved changes in the degree of developmental plasticity, such that a more robust development in response to thermal variation was observed for a broad suite of morphological and life-history traits. Our findings have implications for understanding the mechanisms that facilitate expansion into a novel ecological niche in seasonally variable climatic conditions.