Patterns of fluctuating asymmetry in the limbs of anurans

It has been hypothesized that fluctuating asymmetry (FA) may provide an indication of the functional importance of structures within an organism, with structures that more strongly impact fitness being more symmetric. Based on this idea, we predicted that for tetrapods in which the forelimbs and hindlimbs play an unequal role in locomotion, the less functionally important limb set should display higher levels of FA. We conducted a multispecies test of this hypothesis in anurans (frogs and toads), whose saltatory locomotor mode is powered by the hindlimbs. We also tested whether FA in the forelimbs, which play a more important role during landing, differed between families that differ in the degree of forelimb use in locomotion (Bufonidae vs. Ranidae). We calculated FA from the lengths of humeri and femora measured from disarticulated skeletal specimens of four anuran taxa (Bufonidae: Anaxyrus americanus, Rhinella marina; Ranidae: Lithobates catesbeianus, Lithobates clamitans). Our findings were consistent with the hypothesis that natural selection for increased locomotor performance may influence patterns of FA seen in vertebrate limbs, with all species displaying lower mean FA in the hindlimbs. More subtle functional roles between the forelimbs of bufonids and ranids, however, did not elicit different levels of FA.