The loss of biological diversity is considered one of the principal environmental challenges of the 21st century, and there are hints that this massive reorganization of food webs could affect how parasites are transmitted among hosts. Parasites are often hidden and can be easy to overlook, but they are ecologically important and ubiquitous - so it is important to understand whether we should expect more or fewer of them as biodiversity disappears. Does biodiversity loss increase the abundance of parasites by eroding natural "checks and balances" on transmission? Or does it decrease parasite abundance by removing the free-living biodiversity on which parasites depend? Answers to these questions are urgently needed if we are to mitigate or prevent an uptick in parasite transmission for ecosystems experiencing biodiversity loss. In a joint collaborative research project among the University of Washington, Scripps Institution of Oceanography at UC San Diego, and California State University Monterey Bay, we addressed these questions using a dataset of unprecedented size and taxonomic resolution. We sampled parasites of coral reef fishes from 19 replicate islands in the central equatorial Pacific to study how biodiversity and parasite burden covaried. The specific objectives of this study were to: (1) assess the direction and shape of the relationship between biodiversity and parasite abundance, and (2) understand whether there are factors (e.g., parasite traits like transmission strategy or dispersal capacity, host traits like body size, spatial scale of observation) that influence the relationship between biodiversity and parasite abundance. The highlights of this study to date are: (1) We built a dataset of parasite diversity and abundance from >4,000 fish hosts from 19 islands, including eight Society Islands (Moorea, Tahiti, Huahine, Tetiaroa, Raiatea, Tikehau, Rangiroa, Takapoto) and 11 Line Islands (Kingman, Palmyra, Teraina, Tabuaeran, Kiritimati, Jarvis, Malden, Starbuck, Millennium, Vostok, and Flint), which yielded millions of individual parasites across hundreds of parasite species. (2) Results from a subset of these data showed that geographic features, including island area and island isolation, were the best predictors of parasite abundance within the Line Islands archipelago. We also found that life history moderated this relationship. (3) Given that island area was tightly associated with human population density, we cannot say whether island area or human population density is the true driver, but our findings are consistent with a positive influence of human population density / island area on directly transmitted parasites and a negative influence on complex life cycle parasites. This suggests that human impacts might shape the broad geographic distribution of parasites. Research team and benefits to society: We created and published a peer-reviewed, open-access learning module on parasite biodiversity (Claar et al. 2020). This module is designed for undergraduate biology courses and is available in the open-access database of the American Museum of Natural History's Network of Conservation Educators and Practitioners, at this link: https://ncep.amnh.org/index.php/Detail/objects/1071. We ran a paid summer research internship for undergraduates: the Research Internship in Molecular Ecology (RIME). This program placed a group of underrepresented undergraduates in a central research role, as the team used molecular techniques to investigate the dispersal distance of parasite specimens collected from the central Pacific. RIME students spent a total of 15 weeks performing DNA sequencing of parasite vouchers in the Molecular Ecology Lab at California State University Monterey Bay. Each student led an independent research project with molecular data generated from parasite vouchers to address questions in parasite ecology and presented a poster on their project at the CSUMB Undergraduate Summer Research Poster Symposium and the Western Society of Naturalists Meeting. This grant has supported the graduate-level training of three women scientists, one at each collaborating university. Our reach extends beyond the individuals who were funded by the grant (2 PIs, 1 postdoc, 1 PhD student, 2 MS students, 2 laboratory technicians, 1 project supervisor, 6 RIME interns), as we have leveraged other funds and used our network of collaborations to include an additional postdoc, 2 additional PhD students, 1 undergraduate McNair Scholar, and 9 undergraduate research assistants. Conclusions and future directions: Our research will provide the world's first insights into the direction, magnitude, shape, and scale-dependence of the biodiversity-parasite abundance relationship across a diversity of parasite taxa, host taxa, and spatial scales. This study has identified conditions under which biodiversity is likely to be important in determining the abundance of parasites - a fundamental contribution that can be readily extrapolated from our marine focal system to freshwater and terrestrial ecosystems. No prior study has attempted such a comprehensive investigation of how biodiversity-parasite abundance relationships play out in real ecosystems, and this will contribute substantially to a literature that currently relies on empirical evidence from a mere handful of parasite species. Our progress was delayed by COVID-19 and we are continuing to analyze the large dataset we produced and to write manuscripts reporting our findings. Last Modified: 11/03/2023 Submitted by: Stuart A Sandin
©2020 Biological and Chemical Oceanography Data Management Office.