Varying effects of cypermethrin across life history stages in three amphibian species

Background/Question/Methods Aquatic organisms are heavily impacted by agricultural pollutants that enter lakes, ponds and streams through runoff and aerial spray. Peak application of these pesticides coincides with the vulnerable early life stages of some species in aquatic habitats, including amphibians. Their unshelled embryos and semi-permeable larval skin makes amphibians a particularly sensitive vertebrate. We compared sensitivity to environmentally relevant concentrations (control, low: 0.5 ug/L, and high: 5.0 ug/L) of the pyrethroid insecticide cypermethrin in three anurans: Pseudacris regilla (Pacific tree frog), Rana aurora (northern red-legged frog), and Rana cascadae (Cascades frog). Each species was exposed at three life stages (embryonic, early larval and late larval) for 48 hours then subsequently held in clean water for two weeks at which point we measured their mass, snout-vent length (SVL) and behavioral response to prodding.

Results/Conclusions Individuals in all life stages were affected by exposure to cypermethrin, although the effects varied between species and stages. We found that neither hatching nor survival of embryos were affected by cypermethrin. In contrast, survival was reduced in high treatments for all species at the early larval stage and in the late larval stage for Pseudacris. Reduced predator avoidance response (immobility or twisting in response to prodding) was also observed in Pseudacris individuals exposed as embryos to the high treatment of cypermethrin, whereas individuals in the control and low treatments darted away when prodded. No behavioral effects were observed in individuals exposed to cypermethrin during either the early or late larval stage in any species. Inhibited predator avoidance response from exposure during the embryonic stage indicates that although the jelly coating on amphibian eggs may provide sufficient protection to avoid lethal exposure to cypermethrin, harmful quantities are nevertheless able to permeate the embryo. The varying affects of cypermethrin across stages and species highlights the critical need to assess toxicity in all life-history stages of vulnerable species. To focus on one life stage may underestimate or obfuscate species sensitivity.