Limb preference and skeletal asymmetry in the cane toad, 'Bufo marinus' (Anura: Bufonidae)

Abstract

Two forms of skeletal asymmetry were identified in a population of cane toads, 'Bufo marinus', an exotic species in Australia. Fluctuating asymmetry characterised the lengths and weights of the long bones of the forelimbs and hindlimbs. Directional asymmetry was observed in the structure of the pectoral girdle of the toads, with the right epicoracoid positioned ventral to the left epicoracoid in 88% of the skeletons examined. Morphological data from a cohort of individuals were correlated with limb preferences determined from 10 consecutive trials in which the toads were inverted and briefly submerged in water while bilaterally clasping the experimenter’s fingers. The toad’s left forelimb was released first to enable the right forelimb to exert force against the experimenter's fingers and so control righting the body of the toad in 90% of trials. Asymmetries in the long bones of the forelimbs and pectoral girdles of the toads did not correlate significantly with the strength of preference for the right forelimb, although asymmetry of the weight of the tibiafibulae did correlate significantly with percent right forelimb preference. Age, or nutritional status, was a factor in the right forelimb preference: the preference for the use of the right forelimb was strongest in toads possessing longer and heavier long bones of both the forelimbs and hindlimbs. These results provide insight into the interaction between skeletal development and lateralised motor behaviour in an anuran species.