Environmental deterioration increases tadpole vulnerability to predation

Abstract

Human-induced environmental change is occurring at an unprecedented rate and scale. Many freshwater habitats, in particular, have been degraded as a result of increased salinity. Little is known about the effects of anthropogenic salinization on freshwater organisms, especially at sublethal concentrations, where subtle behavioural changes can have potentially drastic fitness consequences. Using a species of Australian frog (Litoria ewingii ), we experimentally examined the effects of salinization on tadpole behaviour and their vulnerability to a predatory dragonfly nymph (Hemianax papuensis). We found that tadpoles exposed to an ecologically relevant concentration of salt (15% seawater, SW) were less active than those in our freshwater control (0.4% SW). Tadpoles in elevated salinity also experienced a higher risk of predation, even though the strike rate of the predator did not differ between salt and freshwater treatments. In a separate experiment testing the burstspeed performance of tadpoles, we found that tadpoles in saltwater were slower than those in freshwater. Thus, it would appear that salt compromised the anti-predator response of tadpoles and made them more susceptible to being captured. Our results demonstrate that environmentally relevant concentrations of aquatic contaminants can, even at sublethal levels, severely undermine the fitness of exposed organisms.

Assessment of interactive effects of elevated salinity and three pesticides on life history and behavior of southern toad (Anaxyrus terrestris) tadpoles

“…Although we did not assay pesticide concentrations over time in the experimental jars, carbaryl undergoes rapid degradation under many conditions (e.g., Aly and El-Dib [47] and Boone and Bridges [64]) and the limited effect 40 h after dosing is consistent with carbaryl degradation and a partial recovery of activity. Tadpoles chronically exposed to brackish water also exhibited lower overall activity and spent less time feeding relative to those in freshwater, similar to reductions in activity that have been observed among tadpoles of other species in response to elevated salinities [27,65]. Although the reduction in activity levels among tadpoles reared in brackish water was especially dramatic during the first set of observations, a reduction in activity due to elevated salinity was also apparent during the later observations, particularly when adjusting for proximity to metamorphosis.…”

“…At each observation, we scored behavior as inactive (no movement), feeding (mouth movements coupled with tail undulations), or swimming (any other movement) [49]. We analyzed time spent feeding as the most relevant variable for predicting tadpole growth [49], as well as total time active (¼ time feeding þ time swimming) for consistency with previous studies (e.g., Squires et al [27] and Bridges et al [45]). Observations on exposure day 10 began 40 h after changing solutions and adding pesticides, whereas those on day 21 took place within 24 h of a solution change and dosing.…”

Anuran larval developmental plasticity and survival in response to variable salinity of ecologically relevant timing and magnitude

“…The extra time taken to offset this increased energy consumption may have resulted in tadpoles taking longer to attain the optimal size for metamorphosis (Wilbur and Collins, ). Delaying metamorphosis is considered costly because it may expose tadpoles to an elevated risk of predation, not only due to increased time spent in the larval stage (Williamson and Bull, ) but also because salinity itself can decrease the ability of tadpoles to escape predators (Squires et al, ). In addition, delayed metamorphosis increases the risks associated with pond desiccation (Newman, ) and may also have carry‐over effects that could influence population dynamics (Karraker and Ruthig, ).…”

Explanation for missing limbs in deformed amphibians

“…If predation is occurring at preternatural rates, it could represent changes in amphibian behavior or ontological defenses against predators. Certain types of environmental deterioration, such as increased salinity in freshwater habitats or pesticide contamination, have been shown to increase tadpole susceptibility to predation (Cook, '71;Squires et al, 2008). Organic pollution resulting in eutrophication could facilitate plant growth and increase food and shelter for tadpoles and other organisms, providing resources to support growth of both predator and prey populations in wetlands.…”