Research

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  Parasite manipulation of host phenotype

  How does behavior influence risk of infection? How does infection change host behavioral type and behavioral syndromes? Are there positive feedbacks between behavior and infection?

  “Tell me what parasites you have, and I’ll tell you who you are.”
  – Claude Combes (Parasitism: The Ecology and Evolution of Intimate Interactions)

  Nearly all animals in nature are infected by parasites. In both human and non-human animals, an individual’s behavior influences the number and types of parasites it encounters. Once individuals are infected, their behavior may change due to pathology, adaptive responses by the host to reduce the costs of infection, or due to manipulation of host phenotype by the parasite.

  Despite excitement about parasite manipulation of host behaviors, few empirical studies have directly examined how parasites influence host behavioral type (e.g., how active an individual is) and behavioral syndromes (i.e., population-level correlations between behaviors). For my dissertation I am using controlled infections, high throughput behavior assays, and mesocosm experiments to quantify how killifish behavior influences risk of infection with EUHA, and how EUHA subsequently changes individual behavior and population correlations between behaviors. Additionally, I’m running mesocosm experiments to look for feedbacks between behavior and infection under semi-natural conditions. That is, I’m looking to see if parasites change killifish behavior in ways that make the killifish more likely to encounter additional parasites. These types of positive feedbacks can maintain variability in behavior. Understanding how interactions between parasites and hosts shape behavior is crucial for an ecologically relevant understanding of host phenotype.

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  How do parasites manipulate host phenotype?

  How do parasites manipulate killifish neurotransmitter activity? Does infection alter release rates of cortisol (a stress hormone)?

  Manipulative parasites induce phenotypic changes in their hosts that neuroscientists cannot recreate in the lab. These parasites can be thought of as evolutionary neuroscientists, and understanding the mechanisms through which they manipulate host phenotype may reveal previously unexplored links between the immune system, brain, and behavior.

  EUHA infection is associated with baseline changes in neurotransmitter activity and a suppression of the serotonergic stress response in California killifish. To explore how EUHA induces these changes in neurotransmission, Dr. Øyvind Øverli (Norwegian University of Life Sciences) and I conducted a pilot study quantifying the metabolome of various brain regions. We discovered brain-region specific differences in the metabolome of infected and uninfected fish, and are working to identify these compounds and determine their relevance for changes in neurotransmitter activity.

  Changes in neurotransmitter activity could result from parasite manipulation of hormones or vice versa, or both. I thus predicted that infection would be associated with changes in cortisol (a stress hormone). In collaboration with Dr. Ryan Earley (University of Alabama), I validated a non-invasive hormone collection technique that extracts hormones from the water in which a fish has been held for an hour. Water-borne release rates of cortisol mirrored concentrations of these hormones in the plasma, revealing that water-borne hormone release rates are biologically relevant. I discovered that an interaction between EUHA density and handling stress is an important predictor of cortisol release rates (Weinersmith et al., in prep). We thus observed stress-associated, but not baseline differences in steroid hormone release rates.

  To confirm that observed changes in hormone release rates were induced by EUHA and to explore their impact on killifish behavior, I measured baseline and stress-associated cortisol release rates and conspicuous behaviors before infection, and again at 1, 2, 4, and 6 weeks post-infection. Once behavioral video analysis and hormone assays are complete, this experiment will distinguish between killifish-induced and parasite-induced changes in cortisol release rates.

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  Ecology of EUHA

  Does EUHA experience the "crowding effect" in its killifish host?

  The host is its parasites’ ecosystem, and interactions within the host have implications for parasite fitness. The number of EUHA infecting the brain of an adult killifish can exceed 5000, and my collaborators at the UCSB Ecological Parasitology Lab and I were interested in seeing if EUHA compete for resources when they are “crowded” by conspecifics. We observed that EUHA volume (an indicator of adult egg production in other trematode systems) increased with increasing EUHA density, suggesting that EUHA does not experience intraspecific competition at ecologically relevant densities, and may benefit from the presence of conspecifics (Weinersmith et al., in press). Thus, interactions in the killifish host likely do not limit EUHA population size.

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  Invasion biology

  What factors facilitate the establishment and spread of invasive species?

  Invaders helping invaders: Largemouth bass and Egeria densa in the Sacramento San Joaquin Delta
  
  Populations of largemouth bass (Micropterus salmoides) and other centrarchid species have been expanding rapidly in the Sacramento San Joaquin Delta concurrent with a decline in species that occupy the pelagic zone. This shift from a pelagic to a littoral-dominated fish community coincided with the expansion of an invasive submerged aquatic macrophyte, Brazilian waterweed (Egeria densa). We are using electrofishing surveys and diet content analysis to better understand the relationship between Egeria densa and largemouth bass in the Delta, and the implications of this relationship for the native fish community. This work is funded by the Interagency Ecological Program, and is led by Louise Conrad at the CA Department of Water Resources.

  The importance of personality in the invasion biology of the western mosquitofish

  Many species are regularly introduced into novel habitats, but only a subset of these species are able to thrive and expand into nearby habitats. A major goal of invasion biology is to identify the traits that allow this subset of introduced species to successfully invade novel habitats. My collaborators and I explored how behavioral traits, particularly sociability, influence invasion dynamics in western mosquitofish (Gambusia affinis), a fish which is invasive in over 40 countries. We found that asocial fish (i.e., fish that spent less time in close contact with conspecifics) led the invasion front in a series of outdoor connected pools, and that the behavioral composition of a school was important in determining whether or not individuals left to explore new habitats. This work was featured in Nature’s Research Highlights and in Conservation Magazine, and was done in collaboration with Julien Cote, Sean Fogarty, Tomas Brodin, and Andy Sih.

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  Life history of smallmouth bass

  How do behavior and decisions about when and where to build a nest influence the reproductive success of male smallmouth bass?

  Life history of smallmouth bass (Micropterus dolomieu)

  Long-term ecological studies that follow an entire population through multiple generations are powerful tools for understanding ecological and evolutionary processes. We followed a population of male smallmouth bass through multiple generations in a research lake in northern Wisconsin. Each year we used snorkeling and SCUBA to catch all breeding males in the population and collected data on their age, weight, length, and reproductive success. We also quantified characteristics of their nest, including information on substrate (e.g., gravel, rock, or sand) and temperature. All reproducing males in the populations are individually tagged, allowing us to follow males from year to year. We are currently analyzing our multi-year dataset to ask questions about life history decisions and their fitness implications. This project is run by Dr. Daniel Wiegmann of Bowling Green State University, Dr. Jeffrey Baylis of the University of Wisconsin, Dr. Lisa Angeloni of Colorado State University, and Steven P. Newman at the Wisconsin Department of Natural Resources. More information about this project can be found here.