Turning into frogs: Asymmetry in forelimb emergence and escape direction in metamorphosing anurans

摘要

There is considerable debate about the pattern and origin of laterality in forelimb emergence and turning behaviour within amphibians, with the latter being poorly investigated in tadpoles around metamorphic climax. Using 6 species of metamorphosing anurans, we investigated the effect of asymmetrical spiracle location, and disturbance at the time of forelimb emergence, on the pattern of forelimb emergence. Turning behaviour was observed to assess whether motor lateralization occurred in non-neobatrachian anurans and was linked to patterns of forelimb emergence. Biases in forelimb emergence differed among species, supporting the hypothesis that asymmetrical spiracle position results in the same asymmetry in forelimb emergence. However, this pattern only occurred when individuals were undisturbed. Therefore, context at the time of the emergence of the forelimbs may be important, and might explain some discrepancies in the literature. Turning biases, unconnected to forelimb emergence, were found in Pipidae and Bombinatoridae, confirming the basal origin of lateralized behaviour among anurans. Turning direction in our metamorphs differed from the leftward bias commonly observed in tadpoles, but may be analogous to the prevalent right-handedness among adult anurans. Therefore, the transitions occurring during metamorphosis may affect lateralized behaviour and metamorphosis may be fruitful for understanding the development of lateralization.