Environmental DNA for characterizing pollinator biodiversity of vulnerable plant communities

A cornerstone of rare plant conservation, especially for flowering plants, is understanding the mechanisms and biodiversity of pollinators to facilitate species recruitment and ensure populations are maintained. This is particularly important in Hawaii where many of the native pollinators are extinct and non-native, invasive species abound. Unfortunately, conventional methods of pollinator monitoring are often time consuming, require high taxonomic expertise, and struggle to identify pollinators to the species level. To address these limitations, environmental DNA (eDNA) analysis has been shown to be an effective and efficient method for assessing pollinator biodiversity. Here we utilize an eDNA metabarcoding analysis to elucidate pollinator (arthropod and avian) biodiversity on Hawaiian native plants. We collected 276 flower swabs (rare species) or flower washes (more abundant species) from threatened/endangered species, common native species, and invasive species across the Wai' anae Mountain Range on Oahu, totaling 88 plant species sampled. We documented a high diversity of arthropod species (180 unique species) associated with sampled plants, including numerous native and non-native pollinating species, arthropod pests, and arthropod predators. Further, we found that washing typically resulted in higher detected arthropod diversity than swabs and that pollinator species diversity varied across both sampling locations and plant species. These results highlight the applicability of eDNA for assessing pollinator diversity while shedding light on the pollinator communities associated with at-risk and invasive plants on Hawai'i.