A macroevolutionary perspective on species interactions in the carnivorous pitcher plant genus Sarracenia
Stephens, Jessica Deene
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How species interactions influence ecological and evolutionary processes has been a driving interest among biologists. My dissertation research has largely focused on understanding the ecological and evolutionary outcomes of plant interactions with insects and microbes, and how these interactions have potentially lead to the diversification of carnivorous plants. I have focused this work on the genus Sarracenia (pitcher plants). Pitcher plants are found in nutrient poor habitats and have evolved complex trapping structures used in attraction, retention, and digestion of prey. Within these trapping structures are communities of microbes that may be involved in digestion of prey. These plants are highly dependent on insects to obtain nutrients, and prey capture can directly affect seed production. This dependence on prey is predicted to create intense competition among sympatric species leading to strong selection on traits related to prey attraction and capture, as well as selection on the plant microbiome to facilitate the digestion of prey. Insight into the patterns and processes of these interactions requires an explicit understanding of evolutionary relationships of interest. Often species level relationships in groups that exhibit highly convergent traits are the result of recent radiations, which can complicate phylogenetic analyses. Therefore, I used a combination of target enrichment and recently developed coalescent methods to resolve relationships in these ‘difficult’ groups. I have used these techniques to resolve species level relationships in both the genus Sarracenia and also Helianthus. The resulting Sarracenia phylogeny was then used to assess whether this group has evolved suites of trapping traits to attract specific prey types through a common garden approach. Results indicate there are in fact strong correlations among suites of traits and the prey captured for each species across the entire genus of Sarracenia. Together these data support the hypothesis of carnivorous syndromes within the genus Sarracenia. Additionally, these plants rely on their microbiota to digest prey. The diversity and structure of these microbial communities is largely unknown. I sequenced the microbiome across all Sarracenia species in a common garden approach to examine whether host species, season, and/or year structured communities. Results suggest that there are significant differences in microbial communities with the majority of variation explained by pitcher plant species. This suggests that the plant is exerting some selection pressure on the microbiome community. Future work examining the proteome of Sarracenia could elucidate this process. Furthermore, experimental approaches across all these interaction types can further our understanding of the evolutionary of carnivory.