The production, development, and clearance of parasites within individual hosts fundamentally shapes the transmission and spread of parasites among hosts. These cross-scale dynamics modulate the ecology and evolution of host-parasite interactions — with implications addressing public health concerns such as the emergence of drug resistance, the use of diet-driven approaches to combat disease ('immunonutrition'), and managing wildlife diseases. In addition to advancing our ability to understand and managing infectious disease, accounting for these cross-scale feedbacks also provides crucial insight into the role of parasites in natural food webs.
To date, most empirical studies tend to focus on a single scale:
the production or clearance of parasites within hosts or the transmission of parasites between hosts.
My work focuses on developing novel approaches (empirical and theoretical) to integrate across these different scales of biological organization. Host resources (or diet) drive both within-host and between host processes. While resources form the cornerstone to ecological questions, they have been largely overlooked in epidemiological studies (especially theory). Understanding how these resource-driven feedbacks (at both the individual and population level) shape the life history traits of both hosts and parasites is a major focus of my research.
This endeavor also allows me to address key ecological questions such as how individual-level variation in key traits of hosts (e.g., size, stage, sex, genotype) determines variation in exposure, susceptibility, and transmission of parasites and how this intraspecific variation scales up to drive population-level dynamics (e.g., the demographic structure and stability of host populations; the invasion, spread, and severity of disease).
By merging two, currently separate bodies of work (consumer-resource and epidemiology), my work illustrates that classical models often miss crucial components of host-parasite interactions because they overlook intraspecific variation.
My approach combines experiments (individual to population level), field surveys, & mathematical models in a few different host-parasite systems and carries implications for both basic and applied biology.
(1) How do links between individual-level variation (e.g., size, stage, genotypic, reproductive mode) and parasites influence:
(2) How does environmental variation (e.g., UVR, resources) alter these interactions and their population-level consequences
I use theory as a guide to understand patterns and processes in natural systems.
My work combines theory from several different fields:
This mix of theory helps to disentangle results that often arise through complex feedbacks and multiple indirect effects.
Select Research Projects
Parasites shape the demography and stability of host populations.
What do the stage structure and stability of host populations have in common? both are parasite-mediated
Synopsis: Across multi-year, multi-lake field surveys and multiple in situ mesocosm experiments where we created experimental epidemics, we show that during epidemics of a virulent fungal parasite (Metschnikowia bicuspidata):
1) host populations become more juvenile dominated
(this decreases overall biomass of a key consumer/resource in aquatic ecosystems and may even increase the host's risk of extinction)
2) Destabilizes host populations by shifting juvenile and adult hosts into more synchronized cycles (which increases overall population variation).
Parasites & Host allocation to sex
How do parasites influence host allocation to sex?
Synopsis: Across a multi-year, multi-lake field survey and a field-deployed mesocosm experiment, we found that a zooplankton host (Daphnia dentifera) appears to increase allocation to sex during fungal epidemics. We then tested two mechanistic drivers of this pattern. Specifically, we evaluated whether: (1) infection-stressed hosts allocate more to sexual reproduction or (2) apparent changes in sex resulted because males resist infection and become overrepresented during epidemics.
We used a combination of field patterns, experiments, and model of infection risk (parameterized with experimental data), to arbitrate our two mechanistic hypotheses. We found no support for the resistance hypothesis; males were not more resistant, hence likely did not escape culling by parasites. Instead, we found that individual female hosts increased allocation to sex when infected. Together, these results advance understanding of the mechanisms driving variation in allocation to sex across natural populations.
Direct & indirect drivers of disease
Using a combination of multi-year field surveys and in situ experiments, my collaborators and I asked:
How do habitat, predators of parasites, host stage structure, and host diversity jointly drive epidemics of the devastating amphibian chytrid fungus?
Parasite evolution, host resources, and population stability
Synopsis: Clay Cressler and I are investigating how host resources and stage structure influence host population dynamics and in turn, how these processes modulate the evolution of parasite life history traits.
To address these questions, we began by integrating an energetic model of disease to identify evolutionarily stable strategies (ESS) using an adaptive dynamics approach.
Our results illustrate that during stable limit cycles, feedbacks between host resources and immune function become particularly important. These feedbacks can lead to the emergence of evolutionary bistability where parasites can evolve a high virulence strategy that strongly stabilizes the host population or a low virulence strategy, that only weakly stabilizes.
Theory typically predicts that parasites should stabilize their host populations, so we were surprised to find the low virulence ESS. It turns out, that this strategy allows the parasite to 'ride the cycles' of their host populations and maintain itself during periods of low host population density.
We are currently working on experiments to test these predictions.
Hite J.L. and C.E. Cressler. Resource-driven changes to host population stability alter the evolution of virulence and transmission. In press. Philosophical Transactions of the Royal Society, B.
Strauss, A.T., J.L. Hite, M.S. Shocket, M.A. Duffy, C.E. Cáceres, and S.R. Hall. Colliding ecology and evolution of the dilution effect: Rapid host evolution rescues hosts from competition and disease but elevates the density of infected hosts. In Press. Proc. Roy. Soc. London B.
Shocket, M.S., D. Vergara, A.J. Sickbert, J.M. Walsman, J.L. Hite, A.T. Strauss, M.A. Duffy, C.E. Cáceres, and S.R. Hall. Past and current temperature jointly influence parasite transmission and shape seasonality of epidemics. Accepted, Am. Nat.
Hite J.L., R. M. Penczykowski, M. S. Shocket, K. Griebel*, A.T. Strauss, M. A. Duffy, C. E. Cáceres, and S.R. Hall. 2017. Allocation, not male resistance, increases male frequency during epidemics: a case study in facultatively-sexual hosts. Ecology. doi:10.1002/ecy.1976
Hite, J.L., S. Fernández-Beaskoetxea, D.C. Medina, J. Bosch, and S.R. Hall. 2016. Joint effects of habitat, predators, host stage structure, and diversity on amphibian chytrid. Proc. Roy. Soc. London B. 283.
Hite, J.L., R.M. Penczykowski, M.A Shocket, A.T. Strauss, P. A. Orlando, M.A. Duffy, C.E. Cáceres, and S.R. Hall. 2016. Parasites destabilize host populations by shifting stage-structured interaction. Ecology 97(2): 439-449.
Strauss A.T., M.S. Shocket, D.J. Civitello, J.L. Hite, R.M. Penczykowski, M.A. Duffy, C.E. Cáceres, and S.R. Hall. 2016. Habitat, predators, and hosts regulate disease in Daphnia through direct and indirect pathways. Ecological Monographs. 86(4), 393-411.
Civitello, D.J., J.L. Hite, and S.R. Hall. 2014. Potassium enrichment stimulates the growth and reproduction of Daphnia. Oecologia 175: 773-780.
Wojdak J. M., J. C. Touchon, J. L. Hite, B. Meyer*, and J. R. Vonesh. 2014. Consequences of induced hatching plasticity depend on predator community. Oecologia 175: 1267-1276.
Civitello, D.J., R.M. Penczykowski, J.L. Hite, M.A. Duffy, and S.R. Hall. 2013. Potassium stimulates fungal epidemics in a freshwater invertebrate. Ecology 94: 380-388.
Hite, J.L., C.A. Rodríguez Gómez, S.C. Larimer, A.M. Díaz–Lameiro, and R. Powell. 2008. Population densities and structural habitat use of St. Vincentian Anoles. The Caribbean Journal of Science 44: 102-115.
In the works (full manuscripts in review/revision, available upon request)
Hite J.L., R. M. Penczykowski, D. J. Civitello, M. S. Shocket, A. T. Strauss, M. A. Duffy, C. E. Cáceres, and S. R. Hall. Parasites shift stage structure of hosts towards more juveniles in a planktonic disease system. In revision
Orlando, P.A., Hite. J.L., and Spencer R. Hall. Disease as a cause of cohort cycles: theory for disease in a physiologically structured host population. In revision
Orlando, P.A., Hite. J.L., and Spencer R. Hall. Stage structure increases opportunities for fluctuation-dependent coexistence. In revision
Outreach: Combining Art & Science
Outreach is an essential component that strongly informs my approach to teaching and research and vice versa.
Since 2014, I have been working with the local Audubon Chapter (Sassafras Audubon Society) where I helped develop a conservation and outreach program 'Swifts in the City' — a collaborative project focused on improving the plight of the chimney swift (a "near-threatened" bird species).
Chimney swift ('the dolphins of the sky') populations appear to be declining quite drastically (i.e., IUCN “near threatened” in the US, COSEWIC “federally threatened” in Canada). While the causes of these declines are multifaceted, a major issue is the loss of breeding habitat (old hollow tree snags, and industrial and residential chimneys).
Through collaborations involving numerous community partners (e.g., local and national Audubon Chapters, community artists, schools, WonderLab museum of science, health, and technology, and numerous funding agencies), we designed, built, and installed eight new breeding habitats "functional sculptures" that mimic freestanding chimneys. We also led numerous outreach projects to:
(1) provide additional breeding and roosting habitat for this endangered bird.
(2) increase awareness and appreciation of this amazing bird and their role in the global food web by combining art and science
For more information on chimney swifts or this project, please visit our website:
Pop-up card from an art-science class on 'City Birds' at Harmony School
Teaching & Mentoring
I have been fortunate to teach a variety of classes and mentor several outstanding undergraduate students.
Three unifying principles guide my teaching and mentoring approach:
(1) combining foundational principles with practical application
(2) guided active learning
(3) quantitative reasoning
I believe this approach helps to ensure a higher level of understanding, critical thinking, empowerment, enthusiasm for learning, and student engagement.
I connect lessons in the classroom to real-world current issues. This approach helps simplify abstract ideas and make them more tangible and applicable for students.
In both the classroom in the lab, I cultivate a supportive interactive environment where students not only become comfortable asking questions but also help each other discover answers and ways to address open questions.