COS 289-2 - Parasite sharing in a complex multi-host system: A comparison of phenology, reproduction, and genetic differentiation between winter ticks from elk and moose in the southern Greater Yellowstone

Abstract: The winter tick (Dermacentor albipictus) is a parasite known for infesting moose (Alces alces) at rates high enough to cause negative health outcomes. Because winter tick impacts on moose are severe and epizootics are associated with milder winters, most research studies and proposed management actions focus on winter tick-moose-climate relationships while often neglecting other host species which may be important drivers of winter tick population dynamics. In the southern Greater Yellowstone Ecosystem, elk (Cervus elaphus) are competent winter tick hosts and can outnumber moose 10:1. To determine the degree to which winter ticks from elk represent an exposure risk for transmission to moose, we examined the infestation patterns, phenological behavior, and genetic evidence for differentiation between populations of winter ticks from both host species.

We counted winter ticks on moose and elk from capture events and mortalities in Jackson, WY from 2020-2022. Fed adult winter ticks collected from moose (n = 24) and elk (n = 21) carcasses in Spring 2022 were also deployed at reproduction monitoring sites in the field and we monitored questing timing and abundances of questing larvae per female in Fall 2022. We used a genome-wide genotyping approach to compare genetic variation between winter ticks collected from moose (n = 10) and elk (n = 10) and identified ~2,000 single nucleotide polymorphisms (SNPs). No significant differences in winter tick infestation rates were observed between elk (average = 145, SD = 58, n = 25) and moose (average = 275, SD = 171, n = 22, t = 0.001, p > 0.1). We did not observe a significant difference in the total number of questing larvae produced by ticks extracted from elk (average = 482, SD = 211) versus moose (average = 251, SD = 71, t = 0.003, p > 0.1) and both populations of larvae began questing within the same two-week window. Results from our preliminary genetic analysis indicate two potential clusters associated with sample location but not host species (Location Cluster F ~ 0.20, p < 0.01, Host Cluster F < 0.0001, p > 0.32). We conclude that elk may play a critical role in winter tick population dynamics and that winter ticks from elk likely represent an exposure risk to moose. Management actions affecting elk movement and abundance in areas where elk and moose overlap, particularly during winter tick transmission seasons, may be important for addressing winter tick infestation impacts on moose.