Intraspecific phytochemical variation in Ceanothus velutinus along an elevational gradient and the associated herbivores

Background/Question/Methods

Phytochemical diversity is an emerging focus of research on plant functional diversity. Recently, we have set forth on quantifying the "phytochemical landscape" (Hunter 2016), to understand how spatial and temporal variation in phytochemistry across multiple scales can affect the diversity of multitrophic interactions associated with Ceanothus velutinus (Rhamaceae). This species is ubiquitous throughout the Sierra Nevada and northern parts of the Great Basin, is a host to nitrogen-fixing bacteria, and is often one of the first species to establish after forest fires. Ceanothus spp. are also known to produce a variety of cyclopeptides, a class of phytochemicals with wide ranging biological activity (ceanothines, Tan and Zhou 2006). Despite its importance to establishing new communities post-fire and known bioactivity, the ecological relevance of Ceanothus phytochemistry is poorly understood. We set up two elevational transects on the eastern slope of the Sierra Nevada mountains near Reno, NV covering an elevational range of 1600m to 2500m. Along these transects we established temporary 10 m plots, recorded plant diversity and lepidopteran herbivore diversity, and collected C. velutinus leaves for chemical analysis. We revisited the plots monthly to collect data. Using an untargeted metabolomics approach we analyzed 500 leaf samples using LC-MS to quantify phytochemical variation along the elevational gradient and seasonally.

Results/Conclusions

Phytochemical variation across spatial and temporal gradients was linked to herbivore community, and phenology. Overall, we found that plot level intraspecific variation in phytochemical diversity mediates herbivore diversity. Using a metabolomics approach, we identified relationships between elevation and flavonoid production that contribute to phytochemical variation. By identifying the contributions of phytochemical variation to herbivore community assemblages across the landscape, we can begin to understand the role of phenotypic variation in the maintenance of interaction diversity.