No abstract

Sampling hides from harvested animals is commonly used for passive monitoring of ectoparasites on wildlife hosts, but often relies heavily on community engagement to obtain spatially and temporally consistent samples. Surveillance of winter ticks (Dermacentor albipictus) on moose (Alces alces) and caribou (Rangifer tarandus caribou) hosts in Yukon, Canada, has relied in part on voluntary submission of hides by hunters since 2011, but few samples were submitted. To enhance sampling efforts on underrepresented moose and caribou hosts, we implemented a three-year citizen science program, the Yukon Winter Tick Monitoring Project (YWTMP), to better engage with hunters in hide sample collection. A combination of in-person and social media outreach, incentivized engagement, and standardized hide sampling kits increased voluntary submissions of moose and caribou hides almost 100-fold since surveillance began. Citizen science samples expanded the northernmost geographic extent of existing sampling efforts for moose by 480 km and for caribou by 650 km to reach 67.5° N latitude. Samples also resulted in new detections of winter ticks on moose hides that are spatially separate to those submitted for other cervids in Yukon. Findings from the YWTMP have provided an essential baseline to monitor future winter tick host–parasite dynamics in the region and highlighted priority areas for ongoing tick surveillance.

Parasites exhibit a diverse range of life history strategies. Transmission to a host is a key component of each life cycle but the difficulty of observing host–parasite contacts has often led to confusion surrounding transmission pathways. Given limited data on most host–parasite systems, flexible approaches are needed for disentangling the obscure transmission dynamics of these systems. Here, we develop a modelling framework for formally testing long‐standing hypotheses regarding how the parasitic nematode Trichinella nativa is maintained at high prevalences in polar bear populations. We evaluated transmission from marine prey, from scavenging terrestrial carrion, from cannibalism and from scavenging on dead infected bears as possible pathways, and assessed their respective importance by comparing model‐projected prevalences for each mechanism against observed total and age‐specific population prevalences in the Southern Beaufort Sea polar bear subpopulation. Cannibalism and the scavenging on conspecifics have previously been assumed to be critical transmission pathways, but despite data scarcity, our model exposes these mechanisms as ineffective across a wide range of plausible parameter values. Instead, our analyses suggest that transmission from the consumption of infected marine prey, and in particular seals, can explain observed prevalence levels by itself, with other transmission pathways likely playing varying small contributing roles. Furthermore, our model suggests that transmission declines with bear age, perhaps due to age‐dependent changes in diet or immunity. By formalising multiple transmission mechanisms in a unified, mathematical framework, we distilled several hypotheses to a likely main mode of T. nativa transmission to polar bears. The specifics of our model are tailored towards the T. nativa‐polar bear system, but the approach is easily generalized; it provides a powerful, quantitative means for ecologists to explore competing hypothesis for parasite transmission and other difficult‐to‐observe animal interactions even in data‐poor systems.