Resetarits Parasite Ecology Lab

We're interested in


The Resetarits Parasite Ecology Lab is located at Barnard College, Columbia University, in New York City. We study parasites communities across multiple scales of organization, from host individuals, to host populations, to entire ecosystems to understand their role in our communities and 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.

Research Projects

Current Projects

Local adaptation to parasite pressures

Across the east coast, the Eastern Mudsnail (Ilyanassa Obsoleta) dominates the tidal mudflats and are infected by a diverse set of trematode parasites. Previous work has demonstrated an inverse latitudinal gradient of infection prevalence and diversity, with the Northeast having significantly higher infection. Current work in the lab seeks to investigate the mechanisms behind this gradient. To do this, we will rear populations in the lab from across this latitudinal gradient and investigate variations in growth and immunity. Additionally, we will conduct field experiments to determine how infection rates differ between Georgia and New York.

Impact of parasites on oyster filtration

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.

Past Projects

Quantifying the effect of parasites on host resource consumption

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.

Environmental Change & 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.

Parasite Behavior

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.

Reproductive (large) surrounded by soldiers (smaller) from the same colony.

Photo by Ryan Hechinger

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.

  • Featured in UC San Diego News, AAAS EurekAlert, Phys Org, and Science Daily.

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.

Host-parasite interactions across scales

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. .

Aquatic Community Ecology - Keystone Community Concept

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.


Current Classes

BC2272 Ecology

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.

BC3590 Senior Seminar

The main goal of this course is to gain proficiency in reading primary literature and in scientific writing. In this course we will study primary literature in disease ecology. Disease ecology is the study of host-pathogen interactions within an ecological context. For instance, how do predators impact disease dynamics of their prey? What is the role of biodiversity in controlling tick-borne diseases? Each week we will read and discuss 2 papers. Students will be assigned to present each paper and lead the class discussion about that topic. In addition, each student will also write one final thesis which will be a review of the primary literature within a specific area of disease ecology.

Past Classes

ECOL3500-3500L: General Ecology + Lab

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.

Students ready for the field!
Student checking pitfall traps for Mark-Release-Recapture study
Student tethering snails for a predation experiment

Summer Coastal Semester

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 on a sunset cruise!
Student learning how to collect data across a transect
Students enjoying the beach on their first night on Sapelo

Lab Members

Dr. Emlyn Resetarits

Dr. Resetarits is an aquatic ecologist and parasitologist. She recieved a B.A. in Environmental Biology from Columbia University and a Ph.D. in Ecology, Evolution, and Behavior from University of Texas at Austin. Full CV.

Current Lab Members

Interested in joining the lab? I am always interested in having undergraduates work in my lab! This can come in a variety of forms including as a volunteer, for credit, or as a part-time job (or full-time job in the summer!). If interested, please email me!

Previous Lab Members


Kailah Massey

REU & Undergraduate Researcher

Estimating parasite biomass in Georgia Streams

Carter Watson

Carter Watson

CURO & Undergraduate Researcher

Investigating how infection alters snail behavior

Will Ellis

Will Ellis

CURO & Undergraduate Researcher

Understanding how parasites alter snail consumption


Taylor English

Undergraduate Researcher

Investigating eusociality in trematodes


Jason Ogbomoh

Former Undergraduate Researcher

Studied how temperature influences host mortality

Public Engagement

STEM Fatale Podcast

“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!

Media Appearences

Research Pictures

Pictures of research organisms, field sites, undergraduate researchers, and experimental designs.


If you are interested in collaborating with me or interested in undergraduate research opportunities, please contact me!


Barnard College, Columbia University, NY, NY