Experimentally induced host-shift changes morphology and fluctuating asymmetry in sex-specific manner in a seed beetle: an experimental evolution approach

Abstract

Host-shift induced stress in phytophagous insects could have effect on developmental destabilization. Indicator of developmental instability is fluctuating asymmetry (FA)- small random deviations between right and left side of bilateral symmetrical traits. In theory, symmetry is subject to sexual selection in insects, since FA is considered as an indicator of male quality. Response to environmental variation is commonly sex-specific and can affect patterns of sexual dimorphism. We performed reciprocal transplant experiment in eight replicated seed beetle (Acanthoscelides obtectus) populations adapted to bean and chickpea. Within the framework of experimental evolution and using the method of geometric morphometrics we: 1. observed the effects of long and short term host-shift on patterns of shape variation of beetles of both sexes and 2. tested hypothesis that both sexes will have a higher level of FA after long or short term change from optimal to suboptimal host. We found that long term host-shift process affected shape in a way that bean adapted beetles had wider and shorter abdomen compared to chickpea adapted ones. Short-term effects are more notable in bean selected beetles, especially in the abdominal region. Bean adapted males had the most canalized development, i.e. the lowest level of FA, compared to chickpea beetles. In chickpea adapted females, difference in level of FA significantly decreased after the short term host-shift. Our work indicates that host-shift process can change morphological aspects of beetles in a sex-specific manner and consequently influence their developmental trajectories.