Predator-specific inducible morphological changes in two Japanese anuran tadpoles

Many organisms exhibit changes in morphology as a response to predation risk (e.g. development of shells in snails, longer spines in dragonfly nymphs, and deeper bodies in fishes, Brönmark and Miner, 1992; Johansson and Samuelsson, 1994; Hoverman, Auld and Relyea, 2005). These inducible morphological changes have been suggested to represent an adaptive response in order to reduce prey vulnerability. Anuran tadpoles also exhibit inducible morphological defence characters, which are sometimes specific to the types of their predators (Teplitsky, Plénet and Joly, 2004; Kishida and Nishimura, 2005; Wilson, Kraft and Van Damme, 2005; Touchon and Warkentin, 2008). Morphological responses of tadpoles are mainly induced by predatory fish and large insects. For example, tadpoles raised together with fish possess shallower tails and deeper tail muscles than tadpoles raised in a nonpredator environment (Wilson, Kraft and Van Damme, 2005; Touchon and Warkentin, 2008). Morphological adaptation in this sense can have a survival benefit for tadpoles due to an increase in swimming speed during predation events. On the contrary, tadpoles faced by large predatory insects (e.g. dragonfly nymphs) often develop deeper tail heights and shallower tail muscles than tadpoles raised in a non-predator environment (Wilson, Kraft and Van Damme, 2005; Touchon and Warkentin, 2008). Dragonfly nymphs, which are ambush foragers, are often the dominant predators in fishless ponds (Wellborn, Skelly and Werner, 1996). Such changes in tail morphology can attract strikes by these nymphs to the more expendable tail region and away from the more vulnerable head and body (Van Buskirk et al., 2003). Characteristics of morphological adaptation in tadpoles are thought to be associated with the balance among other defence strategies. For example, a tadpole species characterized by chemical defences appears not to exhibit defensive behaviour against fish predators (Kats, Petranka and Sih, 1988). Here, we hypothesize that the characteristics of morphological adaptation as a response to predators differ among tadpole species with different defensive traits. In Japan, the Japanese tree frog (Hyla japonica) and the wrinkled frog Glandirana (Rana) rugosa have been observed together in both temporary and permanent water bodies inhabited by both fish and dragonfly nymph predators. Glandirana rugosa is known to employ chemical defences against fish predators, as chemicals on the skin improve survival during and after attacks Herpetology Notes, volume 5: 43-47 (2012) (published online on 4 March 2012)