Chambers, C. L. | Search bioRxiv

bioRxiv2021

Environmental drivers of body size in North American bats

Bergmanns Rule--which posits that larger animals live in colder areas--is thought to influence variation in body size within species across space and time, but evidence for this claim is mixed. We tested four competing hypotheses for spatio-temporal variation in body size within bat species during the past two decades across North America. Bayesian hierarchical models revealed that spatial variation in body mass was most strongly (and negatively) correlated with mean annual temperature, supporting the heat conservation hypothesis (historically believed to underlie Bergmanns Rule). Across time, variation in body mass was most strongly (and positively) correlated with net primary productivity, supporting the resource availability hypothesis. Climate change could influence body size in animals through both changes in mean annual temperature and in resource availability. Rapid reductions in body size associated with increasing temperatures have occurred in short-lived, fecund species, but such reductions likely transpire more slowly in longer-lived species.

ecology↗

bioRxiv2020

Relatedness and genetic structure of big brown bat (Eptesicus fuscus) maternity colonies in an urban-wildland interface provides insight into rabies transmission dynamics

Big brown bats (Eptesicus fuscus) are the bat species most frequently found to be rabid in North America and are a key source of sylvatic rabies in wildlife. Females can form summer maternity colonies in urban areas, often using access holes in the exterior of buildings to roost in relatively large numbers. In Flagstaff, Arizona, these roosts are commonly found in houses adjacent to golf courses, where habitat quality (food, water, shelter) is high for bats and for mesocarnivores such as striped skunks (Mephitis mephitis) and gray foxes (Urocyon cinereoargenteus). Periodic rabies outbreaks in Flagstaff involving all three of these mammals are primarily caused by an E. fuscus variant of the disease. However, little is known about E. fuscus social behavior during the summer months and how it may drive space use and hence disease exposure to conspecifics and mesocarnivores. To address this knowledge gap, we collected 88 unique genetic samples via buccal swabs from E. fuscus captured at four maternity roosts surrounding a golf course during summer of 2013. We used 7 microsatellite loci to estimate genetic relatedness among individuals and genetic structure within and among colonies in order to infer whether females selected roosts based on kinship, and used genetics and radio telemetry to determine the frequency of roost switching. We found roost switching through genetics (two mother and adult daughter pairs at the same and different roosts) and telemetry, and no evidence of elevated genetic relatedness within colonies or genetic structure between colonies. These results have important implications for disease transmission dynamics in that social cohesion based on relatedness does not act to constrain the virus to a particular roost area. Instead, geographic mobility may increase disease exposure to neighboring areas. We discuss mitigating actions for bat conservation and public health.

ecology↗