Time to feed: How diet, competition, and experience may influence feeding behaviour and cannibalism in wood frog tadpoles

The researchers began this study describing anuran tadpoles as “eating machines”. Because tadpoles are born in wetlands, they have to be capable of adapting to varying conditions. These habitats are subject to changes such as drying out and inherently have varying food availability for tadpoles. These conditions make it a challenge for tadpoles to survive to adulthood. One option for tadpoles is to use cannibalism as a way to increase their chance of survival by reducing competition and providing a food source. Even though cannibalism increases food availability for tadpoles, it also increases their chance of getting diseases.

Wood frog tadpoles, Lithobates sylvaticus, are known to be efficient predators of amphibian larvae, including their own, even though they lack the morphological characteristics seen commonly in cannibals. The researchers in this study aimed to provide knowledge on the proximate causes of cannibalistic behavior in larval amphibians by examining if wood frog tadpoles cannibalize based on specific dietary cues and competitors. The wood frogs used in this study were collected as eggs from wetlands in Canada. The experiment consisted of placing the wood frog tadpoles in containers and tested for different feeding initiation times. Tadpoles were presented with varying conditions of presence/absence of competitors, chemical cues, and various diets such as high and low protein content.

The results of this study showed various eating habits in wood frog tadpoles. Tadpoles responded differently to diets over time, but consistently showed reduced feeding when competitors were present. When tadpoles were presented with specific diets, the response time to conspecific tissues declined. The wood frog tadpoles had the shortest feeding initiation time to brine shrimp, conspecific tissues combined with chemical cues from brine shrimp, and conspecific tissues combined with chemical cues from cornmeal. Wood frog tadpoles had the longest response time to a diet of cornmeal.

This study showed that wood frog tadpoles have the inherent ability to adjust their feeding responses, which helps increase their fitness. The results supported the researchers’ hypothesis that wood frog tadpole cannibalism is affected by chemical cues in their diet and the presence/absence of competition. The authors believe that the tadpole’s sensitivity to competition may lead to aggressive behavior from tadpoles, which can result in intraspecific predation. Because this behavior limits tadpole population density it provides a “profitable” diet to established larvae.

I think that this research is very important to the field of herpetology because it presents further evidence to our understanding of why tadpoles cannibalize. As the authors state, cannibalism impacts the population density of wood frogs and therefore is important to understanding their life history. The research presented in this article helps us further understand the plasticity tadpoles show with cannibalism. I thought that this study provided interesting data on what prompts tadpoles to cannibalize and shows people an interesting behavior found in the animal kingdom.

Jefferson, D. M., Hobson, K. A., & Chivers, D. P. (2014). Time to feed: how diet, competition, and experience may influence the feeding behaviour and cannibalism of wood frog tadpoles (Lithobates sylvaticus). Curr Zool.

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