Northern Red-legged Frog Rana Aurora Research Articles

Co-exposure to multiple ranavirus types enhances viral infectivity and replication in a larval amphibian system.

Multiple pathogens commonly co-occur in animal populations, yet few studies demonstrate how co-exposure of individual hosts scales up to affect transmission. Although viruses in the genus Ranavirus are globally widespread, and multiple virus species or strains likely co-occur in nature, no studies have examined how co-exposure affects infection dynamics in larval amphibians. We exposed individual northern red-legged frog Rana aurora larvae to 2 species of ranavirus, namely Ambystoma tigrinum virus (ATV), frog virus 3 (FV3), or an FV3-like strain isolated from a frog-culturing facility in Georgia, USA (RCV-Z2). We compared single-virus to pairwise co-exposures while experimentally accounting for dosage. Co-exposure to ATV and FV3-like strains resulted in almost twice as many infected individuals compared to single-virus exposures, suggesting an effect of co-exposure on viral infectivity. The viral load in infected individuals exposed to ATV and FV3 was also higher than the single-dose FV3 treatment, suggesting an effect of co-exposure on viral replication. In a follow-up experiment, we examined how the co-occurrence of ATV and FV3 affected epizootics in mesocosm populations of larval western chorus frogs Pseudacris triseriata. Although ATV did not generally establish within host populations (<4% prevalence), when ATV and FV3 were both present, this co-exposure resulted in a larger epizootic of FV3. Our results emphasize the importance of multi-pathogen interactions in epizootic dynamics and have management implications for natural and commercial amphibian populations.

Disease associated with integumentary and cloacal parasites in tadpoles of northern red-legged frog Rana aurora aurora

A total of 6830 northern red-legged frog Rana aurora aurora tadpoles were examined under a dissecting microscope for oral disc, integumentary, and cloacal abnormalities in 13 ponds in and near Redwood National Park in northern California. Of these, 163 tadpoles were collected for histopathological investigation, including 115 randomly collected individuals, 38 collected with oral disc abnormalities, and 10 collected due to severe morbidity of unknown etiology. The tadpoles were infected with 8 parasites, including Batrachochytrium dendrobatidis (the amphibian chytrid), trematodes, leeches, and protozoa. Chytridiomycosis was detected at an overall prevalence of 6.4%, but prevalence was higher in tadpoles with oral disc lesions than in those with normal oral discs (43.5% versus 6.1%). Interestingly, infection was associated with some environmental and co-infection risk factors. Individual tadpoles possessed 0 to 5 species of parasites in varying intensities. Apiosoma sp. was the most prevalent (66%) and widespread. Tadpoles infected with B. dendrobatidis had a lower diversity of oral parasites than those uninfected. During the field portion of the study, a large number (approximately 500) of moribund and dead tadpoles was seen occurring at multiple locations within and surrounding Redwood National Park. Ten animals were collected for histological examination and a diverse protozoal infection was discovered, including some known pathogens of fish. This study is the first reporting parasitism and disease in natural populations of northern red-legged frogs.

Evidence from peptidomic analysis of skin secretions that the red-legged frogs, Rana aurora draytonii and Rana aurora aurora, are distinct species

The northern red-legged frog Rana aurora aurora and the California red-legged frog Rana aurora draytonii are traditionally classified together in the same species group. Ten peptides with antimicrobial activity were isolated from norepinephrine-stimulated skin secretions of R. aurora draytonii and purified to near homogeneity. The peptides were identified as belonging to the ranatuerin-2 family (two peptides), brevinin-1 family (four peptides), temporin family (three peptides), and a novel peptide, RV-23 (RIGVLLARLPKLFSLFKLMGKKV) that has limited structural similarity to the bee venom peptide, melittin. This distribution of peptides contrasts with that found previously in skin secretions from R. aurora aurora collected under the same conditions and at the same time of year (one ranatuerin-2 peptide, two brevinin-1 peptides, and one temporin peptide). The variation in amino acid sequences between corresponding R. aurora draytonii and R. aurora aurora peptides is comparable with the variation in sequences of orthologs from other members of the Amerana group of New World ranid frogs ( Rana boylii, Rana muscosa, and Rana luteiventris). It is proposed, therefore, that the red-legged frogs should be regarded as separate species ( R. aurora and R. draytonii) within the Amerana group rather than conspecific subspecies. The data emphasize that amino acid sequences of antimicrobial peptides in skin secretions may be used to infer taxonomic and phylogenetic relationships between species of ranid frogs.

Host-defense peptides isolated from the skin secretions of the Northern red-legged frog Rana aurora aurora

Antimicrobial peptides in the skin secretions of anurans constitute a component of the innate immunity that protects the organism against invading pathogens. Four peptides with antimicrobial activity were isolated in high yield from norepinephrine-stimulated skin secretions of the Northern red-legged frog Rana aurora aurora and their primary structures determined. Ranatuerin-2AUa (GILSSFKGVAKGVAKNLAGKLLDELKCKITGC) showed potent growth-inhibitory activity against a range of Gram-positive and Gram-negative bacteria (minimum inhibitory concentrations <20 μM) but low hemolytic activity against human erythrocytes (50% hemolysis at 290 μM). Brevinin-1AUa (FLPILAGLAAKLVPKVFCSITKKC) and brevinin-1AUb (FLPILAGLAANILPKVFCSITKKC) also showed potent antimicrobial activity but were strongly hemolytic (HC 50<10 μM). Temporin-1AUa (FLPIIGQLLSGLL.NH 2) atypically lacked a basic amino acid residue and showed very weak antimicrobial and hemolytic activity. Its biological function remains to be established. The primary structures of the antimicrobial peptides are consistent with a close phylogenetic relationship between R. aurora, Rana boylii and Rana luteiventris.