Susceptibility of frogs to chytridiomycosis correlates with increased levels of immunomodulatory serotonin in the skin.

Chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), is a skin disease responsible for the global decline of amphibians. Frog species and populations can vary in susceptibility, but this phenomenon remains poorly understood. Here, we investigated serotonin in the skin of infected and uninfected frogs. In more susceptible frog populations, skin serotonin rose with increasing infection intensity, but decreased in later stages of the disease. The more resistant population maintained a basal level of skin serotonin. Serotonin inhibited both Bd sporangial growth and Jurkat lymphocyte proliferation in vitro. However, serotonin accumulates in skin granular glands, and this compartmentalisation may prevent inhibition of Bd growth in vivo. We suggest that skin serotonin increases in susceptible frogs due to pathogen excretion of precursor tryptophan, but that resistant frogs are able to control the levels of serotonin. Overall, the immunosuppressive effects of serotonin may contribute to the susceptibility of frogs to chytridiomycosis.

Ranavirus phylogenomics: Signatures of recombination and inversions among bullfrog ranaculture isolates.

Ranaviruses are emerging pathogens of fish, amphibians, and reptiles that threaten aquatic animal industries and wildlife worldwide. Our objective was to genetically characterize ranaviruses isolated during separate bullfrog Lithobates catesbeianus die-offs that occurred eight years apart on the same North American farm. The earlier outbreak was due to a highly pathogenic strain of common midwife toad virus (CMTV) previously known only from Europe and China. The later outbreak was due to a chimeric ranavirus that displayed a novel genome arrangement and a DNA backbone typical for Frog virus 3 (FV3) strains except for interspersed fragments acquired through recombination with the CMTV isolated earlier. Both bullfrog ranaviruses are more pathogenic than wild-type FV3 suggesting recombination may have resulted in the increased pathogenicity observed in the ranavirus isolated in the later outbreak. Our study underscores the role international trade in farmed bullfrogs may have played in the global dissemination of highly pathogenic ranaviruses.

Genome Sequence of a Ranavirus Isolated from Pike-Perch Sander lucioperca.

The pike-perch iridovirus (PPIV) was isolated in Finland from apparently healthy pike-perch fingerlings during routine disease surveillance. Our phylogenomic analysis revealed that PPIV is the first fish member of a clade of ranaviruses previously described from European and Chinese amphibians.

Multiple introductions of the eastern fox squirrel (Sciurus niger) in California.

Eastern fox squirrels (Sciurus niger) have been introduced into California within the past 130 years. Recently, their range has been expanding at an alarming rate. Genetic diversity was assessed in 101 control region sequences of eastern fox squirrels from three geographic regions within California (Los Angeles County, Alameda and Contra Costa counties and Sacramento County) to determine if a single or multiple introductions occurred within California, as indicated by the detection of multiple haplotypes. A total of 11 haplotypes were discovered, with haplotypes rarely shared among geographic regions and no clustering by region in a haplotype network. This suggests that the introduction to different regions within California came from different source populations within the native range of the species. Haplotype diversity was highest in Los Angeles County. Due to a lack of phylogeographic structure in fox squirrels in their native range, it is difficult to identify the sources of all introductions.