A test of trade-offs in dispersal and reproduction within and between a sister species pair of specialist insect herbivores

Abstract A critical question in understanding the origin of trade-offs and their impact on trait evolution is whether trade-offs between species originate from within-species variation. Despite their importance, studies linking interspecific divergence between closely related species to intraspecific trait variation are still rare. In this study, we describe a trade-off between dispersal and reproductive effort between two sympatric sister species of wasps in the genus Belonocnema (Hymenoptera: Cynipini: Cynipidae) that form galls on live oaks: B. fossoria , which specializes on Quercus geminata , and B. treatae , which specializes on Q. virginiana . Specifically, our results suggest that B. fossoria has evolved reduced flight capability and smaller wings, but a larger abdomen and greater total reproductive effort than B. treatae , which has larger wings and is a stronger flier, but a smaller abdomen and reduced total reproductive effort. Despite these significant morphological and reproductive differences, these traits remain unchanged when transplanting B. fossoria and B. treatae onto the alternative host plant, suggesting that divergence in these traits is likely genetic as opposed to a plastic response to the different rearing environments. However, we did not find evidence of intraspecific trade-offs between wing length and reproductive traits within either B. fossoria or B. treatae , indicating that trade-offs in life history traits between the two species is a result of independent adaptations in response to different environments. Our study informs our understanding of the evolution of trade-offs among life history traits by examining trade-offs at different biological organizations.