Myrmecophagy in a ranid frog Rana rugosa: specialization or weak avoidance to ant eating?

Abstract

We studied diets of an Asian ranid, Rana rugosa, inhabiting three different environments (reservoir, river shoreline, and paddy fields) in Kyoto, Japan. In all the three habitats, ants were the most frequently consumed prey, representing surprisingly similar proportions in both the frequency of occurrence (81.9-85.7%) and the number of total prey items (56.8-59.4%). These values are exceptionally large for Rana, and equivalent to those reported for ant specialists in other families of frogs such as dendrobatids or bufonids. However, R. rugosa consumed ants lower in proportions than those found in the environment, and could not be regarded as purely ant specialists. Instead, we conclude that this species tends to avoid ants more weakly than other species of Rana. Other than ants, larger prey were more and smaller ones less frequently taken in proportion to frog body size, indicating that the frog consumes ants because of its weak avoidance of these abundant potential prey.