Predicting host range evolution: colonization of Coronilla varia by Colias philodice (Lepidoptera: Pieridae)

Abstract

Extensive sympatry is currently arising between the common sulfur butterfly Colias philodice and a potential leguminous host plant, Coronilla varia. In laboratory trials, larval survivorship and growth were higher on the primary host, Medicago sativa than on the nonhost C. varia, but because females reared from C. varia were on average more fecund than females reared from M. sativa, fitness on C. varia (approximately as survivorship times fecundity) was commensurate with fitness on M. sativa. Thus, it is predicted that selection would favor oviposition on C. varia. Significant among-family variation exists for several measures of larval performance on both C. varia and M. sativa, indicating that C. philodice can potentially respond to selection for increased performance on each species. Larval performance was significantly positively correlated across these species, suggesting that selection for increased performance on each species will facilitate, not constrain, evolution of increased performance on the other. -from Author