T’Kai Adekunle, a student from Savannah State University, worked with Dr. Robbie Richards and Dr. Alex Strauss to understand how predators affect disease dynamics in their prey.
Abstract: The healthy herds hypothesis is the idea that predators reduce the spread of disease in prey/host populations. There are three primary mechanisms by which this effect may occur: 1) reduction of host density, 2) selective predation on infected hosts, and 3) predator-driven shifts in host demography. We tested each of these three mechanisms in a study system containing Gambusia affinis (mosquitofish predators), Daphnia dentifera (zooplankton prey/hosts) and Metschnikowia bicuspidata (fungal parasite). Lakes that have more fish predation tend to have smaller epidemics of M. bicuspidata in D. dentifera. However, experiments have not yet demonstrated causality of these patterns, and the relative importance of these three mechanisms remains unclear. We found that one mosquitofish can eat approximately 60 Daphnia after 24 hours of starvation, indicating a strong capability to inhibit disease by reducing host density (mechanism 1). Next, we found that mosquitofish have a strong preference for infected rather than healthy Daphnia. This result likely arose because infected Daphnia appear darker, making them more obvious to the visually-oriented fish predators. This infection-based preference is also likely to reduce disease (mechanism 2). Finally, we found that mosquitofish also have a strong preference for adult rather than juvenile Daphnia. Since adult Daphnia are more likely to be infected, this stage-based preference could further inhibit disease transmission (mechanism 3). Thus, our experiments demonstrated the potential for predation to slow the spread of disease through each of the three healthy herds mechanisms in this predator-prey/host-parasite system.
Adekunle_poster