Genomic Sequencing of Ranavirus Isolates from a Three-Spined Stickleback ( Gasterosteus aculeatus ) and a Red-Legged Frog ( Rana aurora )

Two ranavirus isolates were recovered during a wildlife disease investigation in California in 1996. Preliminary testing at the time of sample collection indicated that the two isolates were identical. Phylogenetic analysis of the full genomes of these two isolates revealed that they are a single strain of frog virus 3.

Shifts in temperature influence howBatrachochytrium dendrobatidisinfects amphibian larvae

Many climate change models predict increases in mean temperature, and increases in frequency and magnitude of temperature fluctuations. These potential shifts may impact ectotherms in several ways, including how they are affected by disease. Shifts in temperature may especially affect amphibians, a group with populations that have been challenged by several pathogens. Because amphibian hosts invest more in immunity at warmer than cooler temperatures and parasites may acclimate to temperature shifts faster than hosts (creating lags in optimal host immunity), researchers have hypothesized that a temperature shift from cold-to-warm might result in increased amphibian sensitivity to pathogens, whereas a shift from warm-to-cold might result in decreased sensitivity. Support for components of this climate-variability based hypothesis have been provided by prior studies of the fungusBatrachochytrium dendrobatidis(Bd) that causes the disease chytridiomycosis in amphibians. We experimentally tested whether temperature shifts before Bd exposure alter susceptibility to Bd in the larval stage of two amphibian species – western toads (Anaxyrus boreas) and northern red legged frogs (Rana aurora). Both host species harbored elevated Bd infection intensities under constant cold (15° C) temperature in comparison to constant warm (20° C) temperature. Additionally, both species experienced an increase in Bd infection abundance when shifted to 20° C from 15° C, compared to a constant 20° C but they experienced a decrease in Bd when shifted to 15° C from 20° C, compared to a constant 15° C. These results are in contrast to prior studies of adult amphibians that found increased susceptibility to Bd infection after a temperature shift in either direction, highlighting the potential for species and stage differences in the temperature-dependence of chytridiomycosis.

Antipredator pheromones in amphibians: a review

Specific chemosignals (pheromones) have an important role in the antipredator behaviour in amphibians and other vertebrates. However, relatively little is known about the occurrence of chemical alarm cues just in amphibians. The site of chemosignals perception is vomeronasal system. The presence of the vomeronasal system in aquatic amphibians indicates that it did not arise as an adaptation to terrestrial life. Predators may inhibit mate search of some species, and male newts probably take greater risks during the breeding season. Field tests demonstrated different responses to male newt extract – probably trade-off that incorporates risk and resource sensitivity. Response to chemical alarm signals has been documented for tadpoles of frog and for several species of salamander. The response of tadpoles to predator includes morphological modifications and influence of coloration, growth and development retardation. Tadpoles of Rana aurora release a chemical that provides conspecifics with an early warning of predator presence. Bufo boreas tadpoles living in the presence of conspecific alarm cues and chemosignals of specific predators reduce the time of metamorphosis in order to reduce the time in the presence of its predators. Presence of conspecific alarm substances in water and predators’ waste products have an important role in the chemical detection of predators by tadpoles of Rana temporaria and Bufo bufo. Tadpoles of Rana utricularia significantly decreased the growth and increased the mortality of Hyla cinerea tadpoles on the basis of behavioral and chemical interference. Rana utricularia tadpoles apparently use both chemical interference and aggressive behavior in securing a competitive advantage over H. cinerea tadpoles. The response of tadpoles of Rana aurora to tadpoles of Taricha granulosa appear be similar to their response to tadpole extract in eliciting alarm, while insect-fed newts would have less of an effect since predators consuming other species may be less of a threat. In some cases (e.g. in Bufo bufo and B. calamita) chemosignals released in response to threat by predators (direct attack or detection of the predator scents) exert their effects across species.

Correlated trait response: comparing amphibian defense strategies across a stress gradient

Animals inhabiting complex environments often contend with multiple stressors that can select for conflicting responses. Individuals can mediate these conflicts by utilizing correlated responses across multiple traits. In aquatic habitats, larval amphibians often face conflicting, simultaneous pressures, such as ultraviolet-B (UV-B) radiation and predators. UV-B radiation and predation risk influence behavior and body color in many amphibian species, altering activity rates, refuge use, and coloration. When both UV-B and predators are present, individuals can avoid conflicts by coupling behavior with body color to form a correlated response. UV-B exposure rates vary along an elevation gradient, thus trait combinations may also vary. We quantified changes in activity rates and body color in two anuran species, the red-legged frog ( Rana aurora Baird and Girard, 1852) (low elevations) and the cascades frog ( Rana cascadae Slater, 1939) (high elevations), during exposure to predator chemical cues (rough-skinned newt, Taricha granulosa (Skilton, 1849)) and UV-B radiation. Rana aurora decreased activity in response to UV-B and became more cryptic over time, while R. cascadae coupled decreased activity rates in response to predators with dark body coloration to screen out UV-B. Both species responded with a correlated trait response, yet employed opposite strategies. This observed species difference may be reflective of differences in stress across habitats and availability of alternative defenses.