Embryonic learning of chemical cues via the parents' host in anemonefish (Amphiprion ocellaris) (#149)
In the tropical and sub-tropical regions of the Indo-Pacific Ocean, anemonefish inhabit species-specific symbiotic anemones, and it has been demonstrated that juveniles of each anemonefish species reach their hosts by recognising chemicals emitted from their symbiotic anemones. This species-specific host-recognition system of anemonefish was experimentally analysed, with a particular focus on the function of imprinting using naive Amphiprion ocellaris juveniles. We demonstrated the embryonic and immediate post-hatching learning of chemical cues via the parents' host in A. ocellaris through a host-exchange experiment with egg batches during hatching. Anemonefish parents lay their eggs immediately adjacent to their host anemone so that the eggs almost always touch the host's body or tentacles which ensures such imprinting. The memory obtained through this imprinting operates at the time when juveniles first search for their hosts in the sea. Unexpectedly, innate recognition was found to exist not only for the two symbiotic host species but also weakly for two non-partner species which A. ocellaris is seldom observed to inhabit. Innate recognition alone is not sufficient to enable juveniles to reach their hosts. Imprinting via the parents' host complements innate recognition, leading to rigid species-specific host recognition. Imprinting by the parents' single host provides a sufficient cue for reaching the two host species. Furthermore, when combined with imprinting, innate recognition of non-partners serves to supplement the recognition of those species, leading to substitute partnerships that are only observed in some localities. In short, innate non-partner recognition is considered to be a type of spare recognition. We will discuss potential functions of imprinting in the host-recognition system and the necessity of clear distinctions between symbiotic and substitute species.