LEARNING AS A FACTOR IN DIET SELECTION BY ELYSIA VIRIDIS (MONTAGU) (OPISTHOBRANCHIA).

Elysia viridis (Montagu) occurs naturally in populations feedingon the fleshy, siphonalean green alga Codium or on the coarse,filamentous green alga Chaetomorpha. Only about half of theE. viridis transferred from Codium to Chaetomorpha in the laboratorywere able to learn to feed on this alga. Handling time decreasedsignificantly during the learning-period. All E. viridis transferredfrom Chaetomorpha to Codium in the laboratory were able to learnto feed on the latter alga. Handling time also decreased withexperience in these animals. Ingestive conditioning occurredin animals transferred from Chaetomorpha to Codium. These animalshad to go through a learning-period again when they were offeredChaetomorpha after 6–9 weeks with Codium Ingestive conditioningwas also evident from preference experiments; animals preferredthe food they had been kept on prior to the experiments. Thesefindings are discussed in relation to optimal diet theory. (Received 14 December 1987; accepted 22 March 1988)