Predation risk of whole-clutch filial cannibalism in a tropical skink with maternal care

Filial cannibalism, the process of eating one's own offspring, is relatively common in some animal species and has been particularly well studied in fishes. However, whole-clutch filial cannibalism committed by terrestrial vertebrate parents has rarely been reported. In this study, I describe the existence of whole-clutch filial cannibalism in the long-tailed skink, Mabuya longicaudata, on Orchid Island, Taiwan. When skinks encountered intruders against which they could defend themselves, such as the egg-eating snake, Oligodon formosanus, and the agamid, Japalura swinhonis, most M. longicaudata females would either attack (O. formosanus) or ignore (J. swinhonis) the predator, but when the frequency of intrusions by the intruder, O. formosanus, increased, whole-clutch filial cannibalism occurred. When females feel threatened by O. formosanus, the best choice (especially for gravid females) may be to eat their entire clutch of eggs. This behavior has evolved in this skink, thus providing a rare case of whole-clutch cannibalism by a mother reptile. Two existing hypotheses (decreasing brood size and brood age) to explain whole-clutch filial cannibalism suggest that cannibalistic parents may eat the entire clutch when the costs of caring outweigh the expected benefits. In the current study, my results suggest that whole-clutch filial cannibalism is primarily induced by the presence of predators. Thus, I suggest a hypothesis of predation risk of whole-clutch filial cannibalism, in which filial cannibalism by M. longicaudata increases as the predation risk to its offspring increases. Copyright 2008, Oxford University Press.