Adaptations of an insect to a novel host plant: a phylogenetic approach

Abstract

1 The importance of behavioural vs physiological adaptations in the evolution of host associations by herbivorous insects is largely unknown. 2 We compared sister species of beetles, one of which, Ophraella slobodkini, feeds on the lineage's ancestral host, Ambrosia artemisiifolia, while O. notulata has shifted to a novel host, Iva frutescens. Assuming O. slobodkini represents the features of the Ambrosia-feeding ancestor, we asked if behavioural and physiological barriers to utilizing Iva existed and if adaptation to these barriers occurred. We also tested for trade-offs between use of novel and ancestral hosts by O. notulata. 3 We found evidence that the ancestor of O. notulata would have been deterred from feeding on Iva and suffered lower conversion efficiency. 4 Ophraella notulata appears to have adapted behaviourally by increasing consumption of Iva, but we did not detect a significant increase in its physiological capacity to use Iva. Additionally, the switch to Iva by O. notulata did not reduce its physiological capacity to use the ancestral host, Ambrosia. 5 Our results suggest that novel host associations may arise from behavioural adaptations, with physiological adaptations a secondary result of behavioural changes. We discuss implications for hypotheses of host shifts and the evolution of specialization.