Ecomorphological associations in Rhinella (Bufonidae, Anura): relationships with anti-predatory strategies.

Morphological evolution associated to ecological characteristics are likely to involve variations in functional aspects that affect reproduction and survival. In the context of anti-predatory strategies, an association is expected between morphological and ecological characteristics. Here we present a study performed using Rhinella species, a genus characterized by considerable variation in body size (SVL), fore and hindlimb (FLIMB, HLIMB) proportions and parotoid shape (PAR). Specifically, we tested for associations among morphological characteristics and interpreted results in the context of prevalence of different anti-predatory strategies (toxicity or escape) in the groups encompassed by this lineage. Reconstructions of ancestral character states provide evidence for declines in SVL at the R. margaritifera and R. granulosa clades that contrast with increments in SVL observed in the R. marina clade. Morphological patterns are also clear for PAR, which is reduced in the R. crucifer clade and in some species of the clades R. marina, R. granulosa and R. margaritifera. Also, variations are observed in the FLIMB (increased in the R. margaritifera clade and reduced in the R. granulosa clade) and in the HLIMB (reduced in the R. granulosa clade and in some species of the R. marina clade). Some morphological relations among traits were found by independent contrasts. FLIMB (R²=0.244, t=-2.614, p=0.014) and HLIMB (R²=0.214, t=-2.842, p=0.008) are negatively correlated with those of PAR. The negative associations between limb lengths and paratoid size suggest that associations between morphological evolution and anti-predatory strategies in Rhinella, as long-limbed phenotypes may be favored in the context of escape, while large parotoids are likely to enhance toxicity.