Olfactory Imprinting to Amino Acids is Unpredictable but Specific.

Olfactory imprinting is evident when animals respond differently to olfactory cues later in life as a result of experiencing those cues during a sensitive window that occurs early in development. The cues can consist of single chemicals or complex mixtures. Responses to mixtures are complicated, as mixtures can contain odorants that evoke dissimilar responses in unimprinted adults. For example, salmon appear to imprint to amino acid mixtures, yet individual amino acids can evoke attraction, avoidance, or indifference. We aimed to dissect how odorants that evoke dissimilar behavioral responses contribute to mixture imprinting. For this, zebrafish were developmentally exposed to L-leucine, L-lysine and L-valine, or β-phenylethyl alcohol (control), grown to adulthood, and then their preference responses to the same chemicals were measured. Imprinting was apparent to β-phenylethyl alcohol, L-leucine, and L-lysine, but not to L-valine. The responses to L-leucine, and L-lysine were opposing as they evoked attraction and avoidance, respectively. As adults, fish imprinted to a mixture of L-leucine, and L-lysine only responded to the same mixture, not its constituents. This supports the contention that an imprinting cue behaves as a unique object, regardless of its complexity. However, the imprinting response to the mixture was biased by the aversive amino acid, which indicates the imprintable constituents can have different weights. For species that use amino acid profiles to guide their migration, it appears the contributions that any given amino acid makes to the mixture may be quite important.