Embryonic olfactory learning in frogs.

We examined the effect of embryonic olfactory experiences on behaviour after hatching in two species of anuran amphibians, Rana temporaria and Rana sylvatica. Odorants (orange and citral) injected into the egg were "learned" by the embryo and subsequently preferred by tadpoles after hatching. The observed preferences were specific to the odours experienced prior to hatching, and tadpoles discriminated between the odour experienced as embryos and a novel odour. The acquired preference was maintained after metamorphosis for those individuals that exhibited a preference as tadpoles. Preferences of tadpoles were also influenced "naturally" by odours present in the water surrounding the developing embryos. The experimentally induced olfactory preferences did not appear to influence the exhibition of sibling recognition abilities. The study represents the first demonstration of "embryonic" learning in amphibians, and the functions and importance of early olfactory learning for amphibians are discussed.