Host use, mutualism and parasitism in the Lycaeides butterfly complex
AuthorScholl, Cynthia F.
AdvisorForister, Matthew L
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Changes in host use in herbivorous insects can lead to diversification, speciation, and changes in other ecological interactions. In the first chapter, larval performance was investigated in three species of <italic>Lycaeides</italic> butterflies and placed into the context of other already studied ecological traits that potentially contribute to reproductive isolation in this system. For the larval performance experiment, caterpillars from seven populations were reared on five host plants, asking if host-specific, adaptive larval traits exist. We found large differences in performance across plants and fewer differences among populations. These patterns of performance are complex and suggest both conserved traits (i.e. plant effects across populations) and more recent dynamics of local adaptation, in particular for <italic>L. melissa</italic> that has colonized an exotic host. Finally, we put larval performance within the context of several other traits that might contribute to ecologically-based reproductive isolation in the <italic>Lycaeides</italic> complex. This larger context, involving multiple ecological and behavioral traits, highlights the complexity of ecological diversification and emphasizes the need for detailed studies on the strength of putative barriers to gene flow in order to fully understand the process of ecological speciation. One ecological factor that could affect diversification in this group is interactions with other trophic levels. In the second chapter, interactions with mutualistic ants and parasitoids were investigated in the context of current adaptation to a new host, alfalfa, within one of the species previously studied, <italic>L. melissa</italic>. Over the course of two summers, caterpillars and mutualistic ants were collected from sites with both native hosts and sites with an exotic host. Our understanding of the natural history of this system was broadened by identifying tending ants to species and parasitoids to subfamily. It was found that parasitoid abundance and diversity varied considerably across space and time; however, the presence of mutualistic ants did not reduce parasitism rates. These studies highlight the importance of investigating ecological interactions, including interactions with other trophic levels, when studying host dynamics and diversification in herbivorous insects.