Hybridization affects life-history traits and host specificity in Diorhabda spp.

Hybridization is an influential evolutionary process that has been viewed alternatively as an evolutionary dead-end or as an important creative evolutionary force. In colonizing species, such as introduced biological control agents, hybridization can offset losses in genetic variation due to population bottlenecks and genetic drift. Increased genetic variation associated with hybridization could benefit biological control programs, by increasing the chances of establishment success. However, hybridization also can lead to the emergence of transgressive phenotypes, potentially including changes in host use; an important consideration when assessing potential non-target impacts of planned agents. In a series of laboratory experiments, we investigated the effects of hybridization between three species of Diorhabda released to control invasive Tamarix (saltcedar), evaluating effects on development time, adult mass, and fecundity over two generations for all three cross types, and over a third generation for one cross. Depending on the cross, hybridization had either a positive or neutral impact on the measured traits. We evaluated preference for the target (saltcedar) relative to a non-target host Tamarix aphylla (athel), and found hybridization influenced preference in two of the three cross types, demonstrating the possibility for hybridization to shape host use. The overall effects of hybridization varied by cross, suggesting that the outcome of hybridization will be difficult to predict a priori.