Incorporating phylogenetic metrics of biodiversity to refine Lyme disease risk models

Abstract

Biodiversity has been linked to reduced disease transmission through the dilution effect process. Traditional ecological measures of biological diversity, such as species richness, are most commonly used to test for the dilution effect. However, such metrics of species diversity do not consider the evolutionary relationship between species, which has important implications for host immune processes and disease transmission. Phylogenetic diversity incorporates the evolutionary relationships of a wildlife community. Host reservoir competency is partly determined by their capacity to mount effective immune responses, which may be phylogenetically determined. As a result, phylogenetic diversity may be a better metric to evaluate the relationship between host diversity and disease transmission, given that closely related species may have more similar pathogen competencies than distantly related ones. Few studies have examined the relationship between phylogenetic diversity and disease transmission, particularly in vector-borne transmission systems. This study seeks to quantify phylogenetic diversity in the western United States Lyme disease system, where the causal agent Borrelia burgdorferi is vectored by the western black-legged tick, Ixodes pacificus. We empirically measured mammalian diversity and tick data over seven years. We collected data on ticks, host community, and infection prevalence with Borrelia burgdorferi and constructed generalized linear mixed-effect models to evaluate the utility of phylogenetic diversity in predicting the prevalence of a tick-borne pathogen. We found that phylogenetic diversity metrics improved our disease prediction models. Predictions of the overall density and infection prevalence of ticks were improved by the addition of phylogenetic metrics, whereas the density of infected nymphs was solely predicted by a phylogenetic metric over traditional species diversity or richness. Our study found that phylogenetic diversity improves statistical predictions of the Lyme disease pathogen and entomological risk in the western United States and may be informative in other contexts and systems as well.