THE EVOLUTION OF MYRMECOPHAGY AND ITS CORRELATES IN POISON FROGS (FAMILY DENDROBATIDAE)

Poison frogs (Family Dendrobatidae) are common leaf litter inhabitants of New World tropical rainforests. The name of this group derives fro m several genera (especially Dendrobates, Minyobates, and Phyllobates) that are aposematically coloured and have toxic skin to varying degre es. Other species in the family, primarily the genus Colostethus, are cryptically coloured and non-toxic. Recent studies have revealed that the toxic compounds in the skin, which are lipophilic alkaloids, may h ave a dietary origin. Diets and associated characteristics, prey size, prey number, and niche breadth, of nine species in five genera, three of which have poisonous species, were examined. Interpretation of the se characteristics in light of an independently constructed cladogram revealed the inclusion of a high percentage of Formicidae (ants) in th e diets of toxic species. Although alkaloids have been reported in sev eral insect groups, more alkaloids are known from ants than any other group. Species in the genus Dendrobates, which are poisonous and have many other derived characters, have diets composed of 50-73% ants, whe reas percentages of ants used by non-toxic species in the genus Colost ethus was 12-16%. Ants are the major prey category consumed by the fiv e poisonous species considered in this study. In general, frogs separa ted into two groups. More basal groups with non-toxic skin and cryptic coloration had diets with low percentages of ants, low numbers of pre y per individual, and high niche breadths, indicating inclusion of a b road range of prey categories in their diets. Species with poisonous s kin and aposematic coloration had diets with large percentages of ants , large numbers of prey per individual, and low niche breadths, indica ting diets with relatively few prey categories. Thus, diet and the sub sequent evolution of uptake systems for alkaloids, may be the primary character that led to the development of toxic skin and permitted apos ematism, leading to radiation of poisonous species.