Rodent-Pika Parasite Spillover in Western North America

Putative climate adaptation in American pikas (Ochotona princeps) is associated with copy number variation across environmental gradients

Improved understanding of the genetic basis of adaptation to climate change is necessary for maintaining global biodiversity moving forward. Studies to date have largely focused on sequence variation, yet there is growing evidence that suggests that changes in genome structure may be an even more significant source of adaptive potential. The American pika (Ochotona princeps) is an alpine specialist that shows some evidence of adaptation to climate along elevational gradients, but previous work has been limited to single nucleotide polymorphism based analyses within a fraction of the species range. Here, we investigated the role of copy number variation underlying patterns of local adaptation in the American pika using genome-wide data previously collected across the entire species range. We identified 37-193 putative copy number variants (CNVs) associated with environmental variation (temperature, precipitation, solar radiation) within each of the six major American pika lineages, with patterns of divergence largely following elevational and latitudinal gradients. Genes associated (n = 158) with independent annotations across lineages, variables, and/or CNVs had functions related to mitochondrial structure/function, immune response, hypoxia, olfaction, and DNA repair. Some of these genes have been previously linked to putative high elevation and/or climate adaptation in other species, suggesting they may serve as important targets in future studies.

Ecology and Management of Plague in Diverse Communities of Rodents and Fleas

Plague originated in Asia as a flea-borne zoonosis of mammalian hosts. Today, the disease is distributed nearly worldwide. In western United States of America, plague is maintained, transmitted, and amplified in diverse communities of rodents and fleas. We examined flea diversity on three species of prairie dogs (Cynomys spp., PDs) and six species of sympatric small rodents in Montana and Utah, United States of America. Among 2896 fleas, 19 species were identified; 13 were found on PDs and 9 were found on small rodents. In Montana, three flea species were found on PDs; the three species parasitize PDs and mice. In Utah, 12 flea species were found on PDs; the 12 species parasitize PDs, mice, voles, chipmunks, ground squirrels, rock squirrels, and marmots. Diverse flea communities and their willingness to parasitize many types of hosts, across multiple seasons and habitats, may favor plague maintenance and transmission. Flea parasitism on Peromyscus deer mice varied directly with elevation. Fleas are prone to desiccation, and might prosper at higher, mesic elevations; in addition, Peromyscus nest characteristics may vary with elevation. Effective management of plague is critical. Plague management is probably most effective when encompassing communities of rodents and fleas. Treatment of PD burrows with 0.05% deltamethrin dust, which suppressed fleas on PDs for >365 days, suppressed fleas on small rodents for at least 58 days. At one site, deltamethrin suppressed fleas on small rodents for at least 383 days. By simultaneously suppressing fleas on PDs and small rodents, deltamethrin should promote ecosystem resilience and One Health objectives.

Vector-Borne Pathogens in Ectoparasites Collected from High-Elevation Pika Populations

The American pika, Ochotona princeps, is projected to decline throughout North America as climate change reduces its range, and pikas have already disappeared from several locations. In addition to climate, disease spillover from lower elevation mammalian species might affect pikas. We sampled pika fleas in Colorado and Montana across elevations ranging from 2896 to 3612 m and screened them for the presence of DNA from rodent-associated bacterial pathogens (Bartonella species and Yersinia pestis) to test the hypothesis that flea exchange between pikas and rodents may lead to occurrence of rodent-associated pathogens in pika ectoparasites. We collected 275 fleas from 74 individual pikas at 5 sites in Colorado and one site in Montana. We found that 5.5% of 275 pika fleas in this study tested positive for rodent-associated Bartonella DNA but that variation in Bartonella infection prevalence in fleas among sites was not driven by elevation. Specifically, we detected DNA sequences from two loci (gltA and rpoB) that are most similar to Bartonella grahamii isolates collected from rodents in Canada. We did not detect Y. pestis DNA in our survey. Our results demonstrate evidence of rodent-associated flea-borne bacteria in pika fleas. These findings are also consistent with the hypothesis that rodent-associated pathogens could be acquired by pikas. Flea-borne pathogen spillover from rodents to pikas has the potential to exacerbate the more direct effects of climate that have been suggested to drive pika declines.