Do not eat your kids: embryonic kin recognition in an amphibious fish

Adult animals of many species often behave in a cannibalistic manner when encountering conspecific offspring. Kin discrimination is critical for avoiding the consumption of one's own offspring or filial cannibalism. Some fishes cannibalize embryos when other nutritional sources are unavailable. We tested the hypotheses that (1) adult mangrove rivulus, Kryptolebias marmoratus, cannibalize conspecific offspring; (2) cannibalism of unrelated conspecifics is more prevalent than filial cannibalism and (3) the drive to cannibalize embryos is associated with nutritional status ('energy-based hypothesis'). We examined cannibalistic behaviours of the self-fertilizing amphibious K. marmoratus in the laboratory using two isogenic strains. Adults recognized kinship of single embryos, cannibalizing unrelated embryos (28% of the time) but not their own. The ability to recognize kin differed between isogenic strains. Thus, genetic differences significantly influenced behaviour. Fasting had no significant effect on cannibalistic behaviours and thus nutritional state is not an important factor driving cannibalism in this species under these conditions. This is the first documented evidence that a fish species can recognize the kinship of an individual embryo. Across the animal world, there are many examples of animals that eat their own offspring (filial cannibalism), but the outcome of such behaviour may be reproductively costly. Other animals may consume offspring belonging to other parents (non-kin cannibalism). The trick is to recognize the difference between your own versus someone else's offspring to optimize reproductive success. Previous studies on fish have shown that parents can assess the relative ratio of kin to non-kin embryos in an entire nest, but the ability to recognize single embryos has not been demonstrated. We have shown that when a self-fertilizing mangrove fish was presented with a single embryo, it never ate its own but consumed unrelated embryos, suggesting that they have the ability to recognize solo relatives at very early stages of development.