Non-parallel morphological divergence following colonization of a new host plant

Abstract

Divergent ecological selection may diversify populations of the same species evolving in different niches. However, for adaptation to result in speciation, the ecologically divergent populations have to experience at least some degree of reproductive isolation. While ecological selection pressures in similar environments are expected to result in convergent adaptation, sexually selected traits may diverge in different directions in different locations. Here, we use a host shift in the phytophagous peacock fly Tephritis conura, with both host races represented in two geographically separate areas, East and West of the Baltic Sea, to investigate convergence in morphological adaptations. We asked i) if there are consistent morphological adaptations to a host plant shift and ii) if the adaptations to secondary sympatry with the alternate host race are consistent across contact zones. We found low, albeit significant, divergence between host races, but only a few traits, including the female ovipositor, were consistently different. Interestingly, co-existence with the other host race significantly increased the degree of morphological divergence, but the patterns of divergence were not consistent across the two sympatric contact zones. Thus, local stochastic fixation or reinforcement could generate trait divergence, and evidence from additional sources is hence needed to conclude whether divergence is adaptive.

Non-parallel morphological divergence following colonization of a new host plant

“…This study was financed by a Wenner-Gren Fellowship, a Crafoord grant and a Swedish Research Council grant to AR. Finally, thanks to BioRXiv for hosting a previous version of this manuscript (Nilsson et al 2021).…”