Cannibalism 2

Abstract
Cannibalistic interactions resulting from indiscriminate predatory behaviour in tadpoles of poison frogs.

Poison frogs in the genus Dendrobates have very small clutch sizes (2-6 eggs, amongst species for which there are data) and typically transport their tadpoles singly to small phytotelmata, such as bromeliad tanks, leaf axils, fallen fruit capsules, and tree holes. Tadpoles of many species are predacious, consuming larvae of insects that use the same microhabitat for breeding, such as giant damselflies and mosquitoes. Previous studies and observations on the behaviour of poison frog tadpoles led us to question whether tadpoles might be cannibalistic. We studied a population of Dendrobates castaneoticus in lowland rainforest in Para, Brazil and additional data was collected on Dendrobates auratus in Nicaragua. At the study site in Brazil, we established a grid of 40 Brazil nut capsules, the microhabitat used by D. castalzeoticus for tadpole deposition. Of 42 tadpoles deposited during the 55 days of the study, 20 were killed or died; 16 presumably killed by conspecific tadpoles. Growth rate and time to metamorphosis was higher among tadpoles that consumed three or more tadpoles or relatively large larvae of the mosquito Trichoprosopon digitatum, a colonist of newly opened Brazil nut capsules. We propose that selection has favoured the development of predatory behaviour in poison frog tadpoles primarily as a mechanism to eliminate predators from the small phytotelmata in which they develop and that cannibalism is a secondary outcome of this behaviour. Predatory behaviour also provides tadpoles with a source of food, which is frequently limited in these microhabitats. Additional studies of the biology of tadpoles of other species of Dendrobates are needed to determine the evolution of predatory and cannibalistic behaviour in the clade.