Host specificity in subarctic aphids

The specificity of parasitic interaction depends on the adaptations of both the host and the parasite. Over time, these interactions evolve and change as a result of an “arms race” between host and parasite, and the resulting species-specific adaptations may be maintained, perpetuating these interactions across speciation events. With speciation and species sorting over time, complex systems of interactions evolve. Here, we elucidate some of these interactions using the aphids (Hemiptera: Aphididae) of Churchill as a model system. We analyzed these interactions by testing for two patterns in host-specificity: monophagy and phylogenetic clustering. We defined monophagy as one species feeding upon a single host plant species, an association which is driven by arms races in morphology, chemical resistance/tolerance, and camouflage; this pattern was observed in 7 of 22 aphid species. Secondly, we observed three separate cases where groups of closely related aphid species fed upon individual plant species (examples of phylogenetic clustering). One explanation for uncovering species-specific interactions in a recently deglaciated, sub-arctic locality is that the species involved in the associations moved north together. Testing different levels of specificity in species interactions allows us to accurately elucidate these patterns and gives us insight into where to direct future research.