The Resetarits Parasite Ecology Lab is located at the University of Georgia Marine Institute on Sapelo Island. We focus on putting parasites into a community and ecosystem context. We study parasites communities across multiple scales of organization, from host individuals, to host populations, to entire ecosystems. By combining field surveys, dissections, mesocosms, and lab and field experimentation, our research provides insight into host-parasite interactions, behavioral ecology, and community ecology.

Previous work in the lab has demonstrated that trematode parasites can have large impacts on host resource consumption. Across the east coast, the Eastern Mudsnail (Ilyanassa Obsoleta) dominates the tidal mudflats, reaching extremely high densities and exhibiting top-down control on periphyton. Mudsnails also are infected by a diverse set of trematode parasites. Therefore, we are investigating 1) the diversity and prevalence of trematode parasites across Georgia and 2) how individual trematode parasites impact mudsnail top-down control on periphyton. We will then be combining infection prevalence, host density, and parasite impact to esimate the impact of trematode parasites on periphyton across Sapelo island mudflats.

In collaboration with the Drs. Shelby Ziegler and Jeb Byers, we are investigating how infection with the lethal protozoan diseases, Dermo (Perkinsus marinus) and MSX (Haplosporidium nelsoni), on the filtration abilities of the eastern oyster, Crassostrea virginica.

Historically, parasites have been studied for their negative effects on human and animal health. However, the scientific community is becoming increasingly aware that parasites can have complex effects on ecological communities (Dunn et al. 2012, Mischler et al. 2016), and in some cases can benefit the ecosystem (Davis and Prouty 2019). How parasites alter ecosystem processes and nutrient cycling remains relatively unexplored, despite calls to address this question (Raffel et al. 2008, Hatcher et al. 2012). In addition to the consumptive effects of parasites on host mortality and fecundity, parasites can indirectly impact their communities and environments through changes in host physiology (Bernot and Lamberti 2008), nutrient excretion stoichiometry (Bernot 2013) and behavior (Lafferty and Morris 1996) that have population and community-wide effects (Buck and Ripple 2017). My current work aims to quantify how density-mediated and trait-mediated indirect effects of parasites jointly influence aquatic ecosystems through changes in snail hosts. To do this, I work in two different snail-trematode systems: Helisoma (Ramshorn) snails in artificial wetlands and Pleurocerids in streams (Rosemond et al. 1993). In both systems, I’ve found that infected snails have significantly higher consumption than uninfected snails, increasing their top-down control on these aquatic ecosystems. By combining field surveys of infection prevalence and snail density with lab experiments on algal consumption, we established that up to 20% of snail consumption in stream ecosystems can be directly tied to trematode parasites.

How does temperature influence the indirect effects of parasites on resources? These indirect effects are likely temperature dependent, as ectotherms such as snails are highly influenced by temperature. Using Helisoma snails, I am estimating consumption and mortality of infected and uninfected snails across three temperatures. This allowed me to compare the importance of trait-mediated indirect effects (snail feeding rate) and density-mediated indirect effects across temperatures. I found that at moderate temperatures, increased mortality of infected snails offsets their increased feeding rate, effectively making infected snails resource consumption similar to uninfected snails during the course of the experiment. However, at both higher and lower temperatures, the increased feeding rate of infected snails offsets their increased mortality, causing infected snails to have a larger impact on resources than uninfected snails. This work is novel because it is one of the first to estimate the relative roles of trait- and density-mediated indirect effects of parasites and because it investigates how these effects change with temperature.

Resetarits, E.J., †Ellis W. and J.E. Byers. In press. Opposing roles of lethal- and non-lethal effects of parasites on resource consumption. Ecology and Evolution.

While the effect of parasites on host behavior is relatively well documented, parasite behavior is poorly studied, despite implications for transmission and disease dynamics. In the past decade, an incredible trematode behavior has been discovered: eusociality! Some trematode parasites castrate their snail host and form eusocial colonies (i.e. composed of reproductives and non-reproductive soldiers) within the snail’s gonadal tissue. Can parasites optimize their resource allocation between castes? For my dissertation, I investigated how the threat of competition by other trematodes for individual snail hosts alters the parasite colonies’ investment in soldier defense across multiple spatial scales. My work reveals that trematode colonies respond to competition by investing more in soldiers. As a result of changes in resource allocation, per capita parasite transmission may decrease, e.g. fewer reproductives may be produced, when there are more total parasites in the environment. While this work is at its infancy, evidence suggests that eusociality may be a common trait across Trematoda. Future work in my lab will focus on characterizing eusociality across Trematoda and investigating the evolution of this fascinating behavior. This incredible social behavior of parasites has led me towards jointly writing a book chapter discussing the diversity of parasite behaviors and their potential importance for studying disease dynamics.

Resetarits, E.J., Torchin, M.E., and R.F. Hechinger. 2020. Geographic variation in invasion threat drives allocation to soldiers in social trematodes. Biology Letters. 16:2. PDF.

Resetarits E.J., Bartlett L.J., Wilson C.A., and A.R. Willoughby. Parallels in parasite behavior: the other side of the host-parasite relationship. In: Ezenwa VO, Altizer SA, Hall RJ, editors. Animal Behavior and Parasitism. Oxford University Press; 2022.

Parasite communities are an ideal system to apply metacommunity theory. Just like traditional metacommunities, hosts can act as discrete patches for parasites and pathogens (Dallas and Presley 2014, Borer et al. 2016). In collaboration with Dr. Daniel Bolnick, we investigated whether the factors structuring parasite communities were consistent across host-individual and host-population scales. To anwer this question, we leveraged a huge dataset of individual Canadian threespine stickleback fish and their parasite infracommunities (community within a given host) from 33 individual populations. We found that the factors predicting parasite richness and abundance were almost exclusively scale-dependent. For example, more limnetic fish had higher abundances of schistosome parasites, but more limnetic populations did not have higher schistosome prevalence. This is likely due to locally evolved host immunity acting exclusively among populations (the scale at which selection can occur) and dampening population level variance. This indicates that host-parasite relationships cannot be generalized across scales.

Bolnick, D.I., Resetarits, E.J., Ballare, K., Stuart, Y.E. and Stutz, W.E. 2020. Host patch traits have scale‐dependent effects on diversity in a stickleback parasite metacommunity. Ecography. doi:10.1111/ecog.04994 PDF.

Bolnick*, D.I., Resetarits*, E.J., Ballare, K., Stuart, Y.E. and Stutz, W.E. 2020. Scale-dependent effects of host patch traits on species composition in a stickleback parasite metacommunity. Ecology. .

Because communities are connected by the movement of organisms, each community is not truly self-contained but instead affects and is affected by neighboring communities (i.e. a metacommunity). The keystone community concept (KCC) posits that there may be certain types of communities (e.g. highly connected, rare habitat) that have a disproportionate effect on the metacommunity when removed from the overall landscape. If policy makers and conservationists were able to identify community traits that predict “keystoneness,” they would be able to determine which habitats are most important to protect. I conducted a large-scale laboratory experiment using aquatic protist microcosms to investigate these questions. I found that removing any community caused metacommunities to be structured by more random processes, although the type of community did not seem to matter. This novel work experimentally tests previously untested theory (KCC) and has strong conservation applications – my findings suggest that habitat destruction will cause metacommunities to become more stochastic, making them harder for policy makers to conserve.

Resetarits, E.J., Cathey, S. and Leibold, M.A. 2018. Testing the keystone community concept: effects of landscape, patch removal, and environment on metacommunity structure. Ecology, 99: 57-67. PDF.

This class is part of UGA’s Marine Biology Spring Semester and is taught at the University of Georgia Marine Institute (UGAMI), located on Sapelo Island, GA. This course is designed to give you an appreciation of the complexity and simplicity of natural systems along with a solid, fundamental understanding of how organisms interact with their environment and other life forms, shaping the world around us. We will examine processes at numerous scales, from individuals to communities and ecosystems. We will conduct ecological research in the field (e.g., Georiga Salt Marshes, Coastal Ecosystems) and learn how to conduct scientific research from start to finish, by collecting data, forming hypotheses, analyzing data, and writing up our research as a scientific article.

The Summer Coastal Semester is a 4-week, 8 credit intensive field experience composed of Methods in Marine Ecology + Lab (ECOL 4225-4225L) followed by Faculty-Mentored Undergraduate Research (BIOL 4960R/ECOL 4960R/ MARS 4960R). Students will be introduced to field and laboratory methods used to investigate marine ecosystems. This course emphasizes methods for identifying and studying marine organisms, oceanographic and coastal marsh sampling, and other field research methods. Major course topics include: organisms of the marine environment; sampling and analytical approaches for studying invertebrates, plants, and plankton; survey tools for the study of marine ecosystems; and data collection from oceanographic vessels.Using the tools and systems learned in ECOL 4225,Students will conduct laboratory and field research under the supervision of a faculty member.

“STEM Fatale” is a biweekly women in science history podcast hosted by myself and Emma Dietrich. Each week we discuss a different historical woman in science and then talk about current research being done by awesome female scientists! http://www.stemfatalepodcast.com/

“They Blinded Me with Science” is an educational radio program on KVRX Austin that features guest researchers and discussion of current publications. During my PhD, I was one of the hosts, DJ Skittles. https://www.tbmws.podbean.com

Science Under the Stars is a free, monthly public outreach lecture series founded and organized by graduate students in the Section of Integrative Biology at University of Texas at Austin. Public lectures are held under the stars at UT’s Brackenridge Field Laboratory, along with kids activities, nature tours, and more! Since 2009 we have hosted over 60 speakers at our public events! https://scienceunderthestars.org/