Graduation Semester and Year
Spring 2026
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Biology
Department
Biology
First Advisor
Matthew Walsh
Second Advisor
Matthew Fujita
Third Advisor
JC Buckner
Fourth Advisor
Alison Ravenscraft
Fifth Advisor
Luke Frishkoff
Abstract
The Healthy Herds Hypothesis suggests the idea that prey populations derive a benefit from their predators: predators reduce the exposure of their prey to infectious disease, both by limiting prey population densities and by eliminating sick individuals. Much research has focused on the balancing effect that predators have on ecosystems. There is a current need for research into whether these effects cause evolutionary shifts in prey populations, where strong predation pressure prevents prey species from evolving physiological tolerance or resistance to infectious agents. Parasites especially often have rapid effects on host evolution, due to exploitative interactions.
I seek to address this research gap by examining the effects of Camallanus infection on Trinidadian killifish, which are known to exhibit evolved responses to predation pressure. The primary objectives for this project are:
1) Determine how killifish populations have evolved in response to this novel invasive parasite.
2) Determine whether this evolved response is moderated by predators.
In my first chapter, I measured how the distribution of Camallanus has changed from 2016 to 2022 across high-predation and low-predation sites. Results show that Camallanus has spread to new rivers and that killifish in low-predation sites are infected more frequently and with more severe parasite infections than killifish from low-predation sites. Additionally, I examined the negative impacts of infection on killifish fitness. In my second chapter, I measured offspring traits to determine whether Camallanus affects parental provisioning and whether predation has moderated the downstream effects of this invasive parasite. Findings suggest that Camallanus infection in parents may alter egg provisioning and some markers of fitness in offspring, although has not had evolutionary impacts. In my third chapter, I conducted a mark-recapture experiment to study whether variation in Camallanus infection prevalence across predation regimes has led to differential evolution of evolved response to the parasite. I identify differences in evolved tolerance to Camallanus infection across populations, finding some evidence that low-predation killifish have a greater ability to compensate for heavy parasite infections than high-predation killifish.
The overarching goal of this study is to quantify the long-term effects of a novel invasive parasite on a population, focusing on whether predation prevents a host population from developing an adaptive response to this parasite. In this study we observe that Camallanus has differentially altered killifish fitness across predation regimes. Ultimately, these findings may provide information on what factors affect whether a host population will be resilient to an invasive pathogen in long-term time scales.
Keywords
Parasitology, Killifish, Healthy Herds Hypothesis, Predation, Evolution
Disciplines
Evolution
License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
Christian, Anne E., "The Presence of Predators Moderates Evolutionary Responses of Trinidadian Killifish to a Novel Parasite" (2026). Biology Dissertations. 3.
https://mavmatrix.uta.edu/biology_dissertations2/3
Comments
Thank you to my advisor Dr. Matt Walsh for all your help and advice!
Thank you also to my committee for your helpful comments and feedback: Dr. Ravenscraft, Dr. Frishkoff, Dr. Fujita, and Dr. Buckner.