No abstract

The aposematic toad genus Melanophryniscus is a polymorphic group with noticeable variation in colour and pattern. Here, we objectively evaluate variation in spectral reflectance and quantify variation in patterning within and among populations of the species M. rubriventris in NW Argentina. We conducted spectrophotometric analysis on 69 individuals and recorded dorsal and ventral pattern morphs of 727 individuals from six populations. We found high divergence in the reflectance spectra, the extent of brightly coloured areas, and the skin alkaloid profiles with no correlation among coloration varieties, alkaloid profiles, and the geographic distance between populations. Our analyses imply subdivision of sampled populations groupings based mostly on different dorsal colorations. Our results also reveal that populations with very similar patterns may differ markedly in colour and vice versa. It is striking that these aposematic toads show a pronounced variation in colour and patterning among and within populations showing individuals with a conspicuous bright dorsal colouration but also morphs with a rather cryptic black or drab colouration. However, the known presence of several alkaloids classes in all populations suggests that all morphs might be equally unpalatable.

Few studies have investigated the level of individual variation in diet composition of poisonous frogs and toads. We compare the diet composition of three populations of a poisonous toad, Melanophryniscus rubriventris, and predicted that toads within a population might be constrained to forage on particular types of alkaloid-containing prey and consequently diets among populations might not diverge from each other. Most important prey categories in the diets of the three populations consisted of the same ground-dwelling arthropods. We found evidence for individuals consuming different arrays of prey types in all populations implying that this "generalist" species is actually comprised of individuals eating different sets of the available range of prey. Formicidae, Acari, and Coleoptera were all important alkaloid-containing prey items in the diets of all populations and individuals, although there were differences in their order of importance among populations and individuals use different sets of the entire range of alkaloid-containing preys. Future research should evaluate individual diet variation in other poisonous anurans taxa given that shifts in diet composition might have important implications for understanding the consequences of alternate foraging strategies in the evolution of defensive strategies among species.