Host-associated hybrid behavior: A novel aspect of postmating isolation in Neochlamisus bebbianae leaf beetles

Ecological speciation is the process by which reproductive isolation arises between populations as a result of divergent natural selection between habitats. Behavioral postmating isolation is caused by behavioral differences in hybrids that lead to decreased fitness. This form of reproductive isolation has rarely been tested even though it could commonly play a role in the speciation process. We investigate this phenomenon in maple- and willow-associated populations of Neochlamisus bebbianae leaf beetles. Behavioral data were collected from ‘hybrid’ and ‘pure’ offspring as they interacted with leaf cuttings from the two parental host plants as well as a non-host. In these assays hybrids exhibited decreased efficiency and decisiveness in using and choosing hosts compared to the pure offspring. Furthermore, hybrids spent more time on the non-host, illustrating transgressive segregation, whereby hybrids exhibit phenotypes beyond the range of either parent. Our results suggest that hybrid ‘confusion’ contributes to host-associated post-mating isolation.