Predation, competition and amphibian body shape

Posted on December 9, 2010

Separate populations of an aquatic species can show striking variations in body shape.  While such differences may be the result of isolation and evolutionary processes (natural selection or genetic drift) they can also arise within a single generation as a result of phenotypic (trait) plasticity.  Laboratory experiments suggest that larval amphibians can modify their development in different ways depending on environmental conditions:  for example, their tails tend to be relatively large in the presence of predators but smaller in the presence of competitors.  However, few studies have been carried out on the importance of phenotypic plasticity in the wild.  The results of a seven-year investigation on eight amphibian species in 59 ponds in Switzerland were generally consistent with trends predicted from experimental studies, in that larvae tended to have relatively large heads and small tails in ponds where densities of amphibian competitors were high, but deeper tails in ponds where predators (dragonflies, beetles, backswimmers, adult newts) were abundant.  The functional importance of these trends, and of variations between species, requires more study, but a large tail fin may help larvae escape from predators or attract predators away from more vulnerable parts of the body, while a larger head and body may increase competitive advantage by improving the efficiency of food capture and digestion.   Changes in body shape were strongly related to year-to-year variations in both predation pressure (especially in the case of frog and toad larvae) and densities of competitors (especially for newt larvae), which suggested that phenotypic plasticity was more important than genetic divergence. 

Reference:  Van Buskirk, J.  2009.   Natural variation in morphology of larval amphibians:  phenotypic plasticity in nature?  Ecological Monographs, 79(4), 681–705.