Evolutionary and Ecological Determinism of Host Specificity in Arthropod Parasites

Understanding why some diseases infect more species than others is crucial for predicting where and when disease will spread, which can inform the management of wildlife, agriculture, and human health. Currently, large scale patterns of host-parasite dynamics are being studied to understand where to look for and how to manage emerging human diseases (Leroy 2005; Benelli 2018). Previous research has used the Global Mammal Parasite Database (GMPD) to look at host breadth—the number and diversity of species a pathogen can infect—for various groups of parasites, e.g. helminths, arthropods, fungi, etc., from a host-centric perspective (Stephens et al. 2017; Park et al. 2018). However, this approach does not allow me to draw conclusions about the evolution of host breadth within a given parasite or among a group of parasites. The Cressler lab has addressed this problem by using a parasite phylogenetic tree to map the generalism scores—how many hosts it can infect and how closely related, in evolutionary time, are the hosts the parasite can infect—on to. With this approach, it will be possible to address how host-breadth evolves within a group of parasites. First, the pattern of host breadth within a group of mammal-infecting arthropods was determined. arthropod data was chosen from the GMPD because arthropods are a common and abundant parasite of mammals, additionally genetic information of these species is well researched and easily accessible. This research will provide a bigger picture of how host-breadth has evolved within arthropod parasites. It is hypothesized that patterns of arthropod host specificity cannot be explained by simple directional evolution towards host generalism, rather that ecological and evolutionary factors interact to produce differences in host-breadth between closely related arthropods. These findings are important for disease management because they could provide explanations into what ecological and/or evolutionary factors inform host-breadth. These factors could then be used as to predict when and from where new diseases will emerge. The results of this study will provide a detailed analysis of possible ecological and evolutionary factors that cause patterns of host-breadth in arthropods. This information is crucial in understanding the transmission risk of arthropod parasites to humans, and the underlying model could provide a basis for understanding the transmission of emerging zoonotic diseases. This project will be carried out under the mentorship of Dr. Cressler, who specializes in disease ecology and evolution, and graduate student Alaina Pfenning