High Prevalence of Borrelia mayonii (Spirochaetales: Spirochaetaceae) in Field-Caught Tamias striatus (Rodentia: Sciuridae) From Northern Wisconsin

Borrelia mayonii is a recently discovered bacterial spirochete that causes Lyme disease and is transmitted by the blacklegged tick, Ixodes scapularis Say (Acari: Ixodidae). To date, B. mayonii has been isolated from two vertebrate host species in Minnesota: field-caught white-footed mice (Peromyscus leucopus Rafinesque; Rodentia: Cricetidae) and American red squirrel (Tamiasciurus hudsonicus Erxleben). Here, we describe the first detection of B. mayonii in field-caught eastern chipmunks (Tamias striatus L. (Rodentia: Cricetidae)) from northern Wisconsin. During our study, we captured 530 unique small mammals and found an infection prevalence of 23.50% in field-caught eastern chipmunks (4/17) and 1.19% in Peromyscus spp. (5/420). Mean larval and nymphal burdens were determined for captured Blarina brevicauda (0, 0), Glaucomys volans (0.29, 0.14), Myodes gapperi (0.27, 0), Napaeozapus insignis (0, 0.25), Peromyscus spp. (1.88, 0.11), T. striatus (1.06, 0.65), and Sorex cinereus (0.09, 0). The high B. mayonii infection prevalence in eastern chipmunks suggests that the species may be an important reservoir for B. mayonii in the Upper Midwest.

Examining Interspecific density-dependent dispersal in forest small mammals

The effects of conspecific densities on dispersal have been well documented. However, while positive and negative density-dependent dispersal based on conspecific densities are often shown to be the result of intraspecific competition or facilitation respectively, the effects of heterospecific densities on dispersal are examined far less frequently. This despite the potential for the analogous processes of interspecific competition and heterospecific attraction to influence dispersal. Here we use 51 years of live-trapping data on deer mouse (Peromsycus maniculatus), eastern chipmunk (Tamias striatus), red-backed vole (Myodes gapperi), and jumping mice (Napaeozapus insignis and Zapus hudsonius) to examine the effects of both conspecific and heterospecific densities on dispersal frequency. In terms of conspecific densities, jumping mice were more likely to disperse from areas of low conspecific densities, while red-backed voles and chipmunks did not respond to conspecific densities in their dispersal frequencies. When considering interspecific density effects, while there were no statistically clear effects of density on dispersal frequency, the effects of chipmunk and jumping mice densities on dispersal by red-backed vole were greater than the effects of conspecific densities, with voles more likely to disperse from areas of high chipmunk densities and low jumping mice densities. Likewise, the effect of chipmunk densities on dispersal by jumping mice was greater than the conspecific density effect. Conspecific densities clearly can affect dispersal by two of these four species, but the effects of heterospecific densities on dispersal frequency are less clear. Based on effect sizes it appears that there is potential for heterospecific effects on dispersal by some species in the community, but future experimental work could elucidate the strength and causes of these relationships.

Epigenetic anticipation for food and reproduction

Physiological changes in anticipation of cyclic environmental events are common for the persistence of populations in fluctuating environments (e.g. seasons). However, dealing with sporadic resources such as the intermittent production of seed masting trees may be challenging unless reliable cues also make them predictable. To be adaptive, the anticipation of such episodic events would have to trigger the corresponding physiological response. Epigenetic modifications could result in such physiological anticipatory responses to future changes. The eastern chipmunk (Tamias striatus) is known to adjust its reproductive activity to match juvenile weaning with peak seed availability of masting trees, which are essential for their survival. We therefore expected that epigenetic changes would be linked to spring reproductive initiation in anticipation for beech seed availability in fall. We correlated the variation of DNA methylation profiles of 114 adult chipmunks captured in May with beech seeds abundance in September, over 4 years, for three distinct populations, as well as individuals sampled twice during reproductive and non-reproductive years. The significant correlation between spring epigenetic variation and the amount of food in the fall confirmed the phenotypic flexibility of individuals according to environmental fluctuations. Altogether, these results underlined the key role of epigenetic processes in anticipatory responses enabling organisms to persist in fluctuating environments.

Dynamics of ground-nest egg depredation by rodents in a mixed-wood forest

Predation is a leading cause of nest failure in birds, which has significant consequences on their population dynamics. Rodents commonly prey on nests in deciduous forest habitats. This has important implications considering how rodent populations fluctuate with changes in resource availability, such as synchronized but intermittent tree-seed production (mast). In this study, we investigated ground-nest egg predation by rodents over 2 years characterized by high and low beech (Fagus grandifolia Ehrh.) seed availability (mast vs. no-mast years). We used artificial nests monitored by motion-sensing cameras on a study site where eastern chipmunk (Tamias striatus (Linnaeus, 1758)) local abundance was known. We placed the artificial nests in areas of high and low chipmunk abundance as proxy of predation risk. Blue Jays (Cyanocitta cristata (Linnaeus, 1758)) depredated the most eggs overall, but rodent population and egg depredation increased in 2018 following the 2017 mast. However, chipmunks were minor predators and their local abundance did not reflect predation risk. Our results highlight the complexity of predation dynamics on ground-nesting birds and the importance of studying them locally and over multiple years.

Influence of Forest Disturbance on La Crosse Virus Risk in Southwestern Virginia

Forest disturbance effects on La Crosse virus (LACV) are currently unknown. We determined the abundance of three LACV accessory vectors (Aedes albopictus, Ae. canadensis, and Ae. vexans) and the primary amplifying host (Eastern chipmunk; Tamias striatus), and tested for LACV prevalence in both vectors and chipmunks, across a gradient of experimental forest disturbance treatments in southwest Virginia. Forest disturbance significantly affected the abundance of LACV accessory vectors, with a higher abundance on disturbed sites for Ae. canadensis and Ae. vexans. However, there was no significant disturbance effect on chipmunk abundance. Forest disturbance significantly affected LACV prevalence in mosquito vectors, with most (80%) detections on unlogged control sites, which past work showed harbor the highest abundance of the two most common LACV vectors (the primary vector Aedes triseriatus, and Ae. japonicus). Interestingly, LACV nucleic acid was only detected in Ae. japonicus and Culex pipiens/restuans, with no detections in the primary vector, Ae. triseriatus. In contrast to the vector results, antibodies were only found in chipmunks on logged sites, but this result was not statistically significant. Overall, our results suggest that human LACV risk should generally decline with logging, and reveal the potential importance of accessory vectors in LACV maintenance in Appalachian forests.