Background
Ranavirus is an emerging infectious disease which has been linked to mass mortality events in various amphibian species. In this study, we document the first mass mortality event of an adult population of Dybowski’s brown frogs (Rana dybowskii), in 2017, within a mountain valley in South Korea.
Results
We confirmed the presence of ranavirus from all collected frogs (n = 22) via PCR and obtained the 500 bp major capsid protein (MCP) sequence from 13 individuals. The identified MCP sequence highly resembled Frog virus 3 (FV3) and was the same haplotype of a previously identified viral sequence collected from Huanren brown frog (R. huanrenensis) tadpoles in South Korea. Human habitat alteration, by recent erosion control works, may be partially responsible for this mass mortality event.
Conclusion
We document the first mass mortality event in a wild Korean population of R. dybowskii. We also suggest, to determine if ranavirus infection is a threat to amphibians, government officials and researchers should develop continuous, country-wide, ranavirus monitoring programs of Korean amphibian populations.
Because of their complex life styles, amphibians and reptiles living in wetlands require both aquatic and terrestrial buffer zones in their protected conservation areas. Due to steep declines in wild populations, the gold-spotted pond frog (Rana chosenica) is listed as vulnerable by the IUCN. However, lack of data about its movements and use of habitat prevents effective conservation planning. To determine the habitat use and home range of this species, we radio-tracked 44 adult frogs for 37 days between 10 July and 4 Nov. 2007 to observe three different populations in the breeding season, non-breeding season, and late fall. The gold-spotted pond frog was very sedentary; its daily average movement was 9.8 m. Frogs stayed close to breeding ponds (within 6.6 m), and did not leave damp areas surrounding these ponds, except for dormancy migration to terrestrial sites such as dried crop fields. The average distance of dormancy migration of seven frogs from the edge of their breeding ponds was 32.0 m. The average size of an individual's home range was 713.8 m(2) (0.07 ha). The year-round population home range, which accounts for the home ranges of a population of frogs, was determined for two populations to be 8,765.0 m(2) (0.88 ha) and 3,700.9 m(2) (0.37 ha). Our results showed that to conserve this endangered species, appropriately sized wetlands and extended terrestrial buffer areas surrounding the wetlands (at least 1.33 ha, diameter 130 m) should be protected.
In recent years, there has been a rapid decrease in amphibian populations worldwide, and infectious diseases have been associated with this decline. Diseased frogs inhabiting Korea were collected from fields, and the diseases were identified by morphological and molecular analyses. Two fungal diseases-saprolegniasis and chromomycosis-were detected in the frogs. Saprolegniasis caused by Saprolegnia spp. was found in Rana plancyi chosenica from Gangwon-do and Rana huanrenensis from Chungbuk. Chromomycosis, which is caused by infection with Cladosporium cladosporioides, was detected in Rana catesbeiana from Busan.
We used field surveys and statistical models to investigate habitat associations of the endangered gold-spotted pond frog (Rana chosenica). The characteristics of its habitat are of great importance for effective conservation for this declining species in western South Korea. We evaluated a priori models that incorporated biotic and abiotic variables at the pond and landscape scales. The best-ranked model predicts that gold-spotted pond frogs will be more abundant at sites with fewer introduced American bullfrogs (Rana [= Lithobates] catesbeianus) and greater coverage of shallow, vegetated water. Our study leads us to conclude that limiting the spread and abundance of bullfrogs has the potential to aid conservation of the gold-spotted pond frog in our region.
Although lizards are important hosts for hard ticks (Ixodidae), very few studies have been conducted in South Korea. To determine whether or not hard ticks can infest lizards endemic to South Korea, we examined 77 lizards of four species (Eremias argus, Sincella vandenburghi, Takydromus amurensis, and Takydromus wolteri) that were collected at 22 different sites between April and October 2010. We confirmed that all four lizard species can be infested by Ixodes nipponensis larvae or nymphs. Of the 62 E. argus examined, we found an average of 12.5 larvae on two lizards and an average of one nymph on one lizard. We found seven nymphs on one S. vandenburghi. We found an average of two nymphs on two of the five T. amurensis and an average of one nymph on four of the nine T. wolteri. Ixodes nipponensis larvae and nymphs were found most frequently on the foreleg axillae (87.8%), followed by the forelegs (7.3%), the eyelids (2.4%), and the ears (2.4%) of the lizards. To the best of our knowledge, this is the first report of I. nipponensis infestations of lizards endemic to South Korea.
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