Ecological speciation and adaptive evolution in a herbivorous mite

Plant-herbivore interactions often promote the evolution of host specialization, where different herbivore types adapt to one or a few closely related plant species. This can prompt the evolution of barriers to hybridization between populations of a herbivore that have adapted to different host species. Only a few herbivore species are known to be generalists, which are able to exploit a large number of unrelated plant taxa. A well-studied example with a world-wide distribution is the two-spotted spider mite, Tetranychus urticae. It causes significant damage to economically-important crops, where extensive use of chemical control agents has led to the evolution of resistance to many different acaricidal compounds. The mechanisms by which generalist herbivores exploit a large number of host species are poorly understood, and research is largely biased towards populations associated to agricultural settings. Across this dissertation, I present evidence supporting the role of host plant adaptation in promoting evolutionary divergence between populations of the two-spotted spider mite that occur in nature. Patterns of genetic variation within and between spider mite populations are investigated in two sites located in the Dutch dunes. I characterize the mechanisms by which mites adapt to honeysuckle, a widespread plant species in this ecosystem, and discuss on how these mechanisms can promote the reproductive isolation of host-associated mite genotypes. In several experimental evolution experiments coupled with whole genome sequencing, the loci that are selected upon host adaptation and acaricide resistance are mapped. I discuss the contribution of genetic evolution to the processes of host adaptation and acaricide resistance, and present several possible avenues for future research.