Effects of Road De-Icing Salts on Two Amphibian Species, Rana Sylvatica and Rana Pipiens, and Their Trematode Parasites

With ongoing amphibian declines, it is essential to determine possible contributors such as diseases and environmental contaminants that may increase susceptibility. A potential contaminant is road salt (mainly NaCl), which leaches into aquatic environments. I examined whether road salts make larval amphibians (tadpoles) more susceptible to trematode parasite infection, and also how these affect free-living trematode infectious stages (cercariae). I exposed Rana sylvatica (wood frogs) and R. pipiens (northern leopard frogs) to control, medium (400 mg/L), and high salt (800 mg/L) treatments, and then to trematodes. High salt tended to reduce wood frog anti-parasite behaviour and resistance to infection but the opposite was seen for R. pipiens, although these tadpoles had elevated lymphocyte counts in high salinity. Trematodes were differentially affected by increased salinities. The results suggest that host-parasite-environment interactions are complex, with species differentially affected by contaminants, which may lead to community shifts in predominant hosts and parasite species.

Effects of Road De-Icing Salts on Two Amphibian Species, Rana Sylvatica and Rana Pipiens, and Their Trematode Parasites

With ongoing amphibian declines, it is essential to determine possible contributors such as diseases and environmental contaminants that may increase susceptibility. A potential contaminant is road salt (mainly NaCl), which leaches into aquatic environments. I examined whether road salts make larval amphibians (tadpoles) more susceptible to trematode parasite infection, and also how these affect free-living trematode infectious stages (cercariae). I exposed Rana sylvatica (wood frogs) and R. pipiens (northern leopard frogs) to control, medium (400 mg/L), and high salt (800 mg/L) treatments, and then to trematodes. High salt tended to reduce wood frog anti-parasite behaviour and resistance to infection but the opposite was seen for R. pipiens, although these tadpoles had elevated lymphocyte counts in high salinity. Trematodes were differentially affected by increased salinities. The results suggest that host-parasite-environment interactions are complex, with species differentially affected by contaminants, which may lead to community shifts in predominant hosts and parasite species.

Comparison of Thermal and Mechanical Noxious Stimuli for Testing Analgesics in White’s Tree Frogs (Litoria caerulea) and Northern Leopard Frogs (Lithobates pipiens)

Determining the clinical efficacy of analgesic drugs in amphibians can be particularly challenging. The current studyinvestigated whether a thermal nociceptive stimulus is useful for the evaluation of analgesic drugs in 2 amphibian species.The objectives of this study were 2-fold: 1) compare 2 models of nociception (thermal and mechanical) using 2 frog species; White’s Tree Frogs (Litoria caerulea; WTF) and Northern Leopard Frogs (Lithobates pipiens; NLF) after administration of saline or morphine sulfate; and 2) evaluate antinociceptive efficacy of morphine sulfate at 2 doses in a common amphibian research species, the NLF, using a mechanical stimulus. Neither WTF nor NLF displayed consistent drug-dependent changes in withdrawal responses to a noxious thermal stimulus applied using the Hargreaves apparatus, but NLF exposed to the noxiousmechanical stimulus demonstrated a significant dose-dependent antinociceptive response to morphine sulfate. These resultsindicate that morphine is not antinociceptive in WTF, supporting previously reported results, and demonstrate the importanceof using an appropriate experimental antinociceptive test in amphibians. Our data suggest that nociception in amphibianspecies may be best evaluated by using mechanical nociceptive models, although species differences must also be considered.