Enhanced survival of a specialized leaf beetle reveals potential trade-offs with host utilization traits

The most evident trade-off in specialized herbivores is the reduction of host range. However, trade-offs that limit the adaptation of specialized herbivores to an evolving host could exist and have been scarcely explored. Here, we tested whether the specialized leaf beetle species Lema daturaphila expresses trade-offs related to its co-adaptation with the host plant species Datura stramonium. Firstly, we found that increases in the concentration of scopolamine, a tropane alkaloid that is produced by the plant species, reduce beetle survival, showing that scopolamine is still a defensive trait against the specialized herbivores. In addition, we performed a selection experiment to increase survival of the beetles on the normal host and explored the consequences for life history and host-related traits and the corresponding G-matrix. After three selection events, we observed an improvement of survival in the selection line, but no correlational selection on other traits. There was also evidence that the G-matrix structure changed after selection. The genetic correlations between fecundity and relative growth rate and consumption efficiency were negative in the selection line, but neutral in the control line. The change in genetic correlations after selection suggests that there are trade-offs between survival and host utilization traits, which have the potential to limit the beetles’ co-adaptation to evolving plant defenses.