Investigating temporal changes and effects of elevation on the prevalence of a rickettsial blood parasite in red-backed salamanders (Plethodon cinereus) in Virginia, USA

Abstract

Amphibians are host to a number of vector-transmitted blood parasites. One parasite for which there is little information is a recently described intracellular bacteria in the order Rickettsiales, found in red-backed salamanders (Plethodon cinereus) in the eastern USA. This parasite was observed in 16.7 % of individuals across three states in the summer of 2008. Here, we resampled one of the locations from the 2008 study (Mountain Lake, Virginia, where site-level prevalence was 22 %) to determine if the incidence of infection has changed in 5 years. We also examined red-backed salamanders at seven other nearby sites that varied in elevation (670–1310 m) to ascertain if the pathogen shows any corresponding variation. We collected a total of 113 salamanders across the eight sites. We found no evidence that prevalence of the pathogen has changed; overall prevalence was 12.4 %, which was not significantly different from the 2008 estimate, and prevalence at the Mountain Lake site (28.6 %) also did not differ from the 2008 estimate. When comparing prevalence across elevations, we found that the highest-elevation sites tended to have highest levels of infections; one in five salamanders was infected with rickettsial bacteria at these locations. Ironically, these high-elevation sites appeared to have the highest salamander densities, and the largest salamanders, which usually point to healthy populations. Since salamander habitats in the Appalachian highlands are predicted to shrink in the future, our results suggest that the remnant, mountaintop populations will remain highly infected with this mysterious parasite.