Populus hybrid hosts drive divergence in the herbivorous mite, Aceria parapopuli: Implications for conservation of plant hybrid zones as essential habitat

Plant hybrid zones receive little conservation attention, yet they may be centers of diversity and evolutionary opportunity for dependent species. In previous studies, cottonwood hybrid zones have been shown to be important drivers of biological diversity and herbivore evolution. Despite these findings, no studies have examined whether hybrid host use drives herbivore genetic divergence across a broad geographic range. Here, we examined the role of Populus hybridization on the evolution of the eriophyid mite, Aceria parapopuli, using ITS1 sequence differentiation. We found support for the hypothesis that Populus hybridization has driven genetic divergence in mites in multiple hybrid zones. Furthermore, our data suggest that hybrid host use has followed at least two instances of mite genetic divergence. Our findings have several important conservation implications. First, they suggest that cottonwood hybrid zones can be important drivers of evolutionary divergence in a dependent herbivore. Second, different hybrid zones represent different ecological environments, and provide independent opportunities for local adaptation and divergence. Although hybrid plants are not considered a high priority for conservation management, and in some cases viewed as "evolutionary dead ends", our results suggest that new consideration ought to be given to plant hybrid zones. As shown here, natural hybrid zones provide unique ecological and evolutionary opportunities, and essential habitat for dependent species, all of which deserve conservation attention and increased protection.