Effects of arthropod inquilines on growth and reproductive effort among metacommunities of the purple pitcher plant (Sarracenia purpurea var. montana)

Anthocyanin Impacts Multiple Plant-Insect Interactions in a Carnivorous Plant

AbstractAlthough there are many hypothesized ecological functions of plant coloration, they have been only partly resolved by examining ecological hypotheses in isolation. Multiple ecological interactions may act in concert or in opposition to fix or maintain variation in plant coloration, that is, via ecological pleiotropy. To investigate the adaptive value of red plant pigment (anthocyanin) in a carnivorous plant, we compared insect prey capture, herbivore damage, and recruitment of specialist insect larvae in naturally occurring sympatric red and green color morphs of the pitcher plant Sarracenia purpurea. We integrated field and laboratory bioassays, visual modeling, chemical analysis of anthocyanins, and a long-term demographic study to investigate multiple ways anthocyanins mediate plant-insect interactions. In support of ecological pleiotropy, each morph performed better in one or more ecological contexts, providing evidence for ecological interactions exerting opposing selection on plant color and thus maintaining variation. The mixture of both ecological benefits and costs to anthocyanin production is further supported by stable color polymorphism and seed set data consistent with balancing selection. More broadly, this work reveals the impacts of a single anthocyanin compound on multiple key plant-insect interactions, demonstrating evidence for ecological pleiotropy maintaining intraspecific diversity in plant color.

Analysis of the northern pitcher plant (Sarracenia purpurea L.) phytotelm bacteriome throughout a temperate region growing season

The insectivorous Northern Pitcher Plant, Sarracenia purpurea, recruits a dynamic biotic community in the rainwater collected by its pitcher-shaped leaves. Insect capture and degradation within the pitcher fluid (phytotelma) has been well documented as a mechanism for supplementing the plant's nitrogen, phosphorous, and micronutrient requirements. Metagenomic studies have shown a diverse microbiome in this phytotelm environment, including taxa that contribute metabolically to prey digestion. In this investigation, we used high-throughput 16S rDNA sequencing and bioinformatics to analyze the S. purpurea phytotelm bacteriome as it changes through the growing season (May-September) in plants from the north-central region of the species' native range. Additionally, we used molecular techniques to detect and quantify bacterial nitrogenase genes (nifH) in all phytotelm samples to explore the hypothesis that diazotrophy is an additional mechanism of supplying biologically available nitrogen to S. purpurea. The results of this study indicate that while prokaryote diversity remains relatively stable in plants at different locations within our region, diversity changes significantly as the growing season progresses. Furthermore, nifH genes were detected at biologically significant concentrations in one hundred percent of samples, suggesting that nitrogen fixation may be an important contributor to the S. purpurea nutrient budget.

Selective Bacterial Community Enrichment between the Pitcher Plants Sarracenia minor and Sarracenia flava

The interconnected and overlapping habitats present in natural ecosystems remain a challenge in determining the forces driving microbial community composition. The cuplike leaf structures of some carnivorous plants, including those of the family Sarraceniaceae, are self-contained ecological habitats that represent systems for exploring such microbial ecology questions. We investigated whether Sarracenia minor and Sarracenia flava cultivate distinct bacterial communities when sampled at the same geographic location and time. This sampling strategy eliminates many abiotic environmental variables present in other studies that compare samples harvested over time, and it could reveal biotic factors driving the selection of microbes. DNA extracted from the decomposing detritus trapped in each Sarracenia leaf pitcher was profiled using 16S rRNA amplicon sequencing. We identified a surprising amount of bacterial diversity within each pitcher, but we also discovered bacteria whose abundance was specifically enriched in one of the two Sarracenia species. These differences in bacterial community representation suggest some biotic influence of the Sarracenia plant on the bacterial composition of their pitchers. Overall, our results suggest that bacterial selection due to factors other than geographic location, weather, or prey availability is occurring within the pitchers of these two closely related plant species. This indicates that specific characteristics of S. minor and S. flava may play a role in fostering distinct bacterial communities. These confined, naturally occurring microbial ecosystems within Sarracenia pitchers may provide model systems to answer important questions about the drivers of microbial community composition, succession, and response to environmental perturbations. IMPORTANCE This study uses amplicon sequencing to compare the bacterial communities of environmental samples from the detritus of the leaf cavities of Sarracenia minor and Sarracenia flava pitcher plants. We sampled the detritus at the same time and in the same geographic location, eliminating many environmental variables present in other comparative studies. This study revealed that different species of Sarracenia contain distinct bacterial members within their pitchers, suggesting that these communities are not randomly established based on environmental factors and the prey pool but are potentially enriched for by the plants' chemical or physical environment. This study of these naturally occurring, confined microbial ecosystems will help further establish carnivorous pitcher plants as a model system for answering important questions about the development and succession of microbial communities.