Food-induced body pigmentation questions the taxonomic value of colour in the self-fertilizing slug Carinarion spp

Body pigmentation is a popular taxonomic marker in slugs to discriminate cl osely related species. However, the genetic background of body pigmentation is known only for a few species, while in many others body pigmentation is influenced by age, food and/or climate. In this study, we investigated the effects of different food items on body pigmentation expression in two sel fing pulmonate gastropods, Arion (Carinarion) silvaticus and Arion (Carinar ion) fasciatus. Both species mainly differ in the distribution of yellow-or ange granules on the body, which in A. fasciatus are concentrated in latera l bands, and in A. silvaticus are evenly scattered. Animals were raised ind ividually under the same conditions, while they laid eggs as a consequence of selfing. This F, generation was afterwards divided into two groups, whic h were fed with different food items. A diet of carrot, lettuce or paper ha d no effect on the distribution of the yellow-orange granules in A. silvati cus, but provoked a loss of the yellow-orange lateral bands in A. fasciatus so that externally these F-1 specimens became similar to A. silvaticus. In both species, a diet of nettle resulted in a strong yellow-orange pigmenta tion, which often formed yellow-orange lateral bands. These results indicat e that food can probably influence the 'species-specific' body pigmentation in Carinarion. and thus question the reliability of colour traits to disti nguish A. silvaticus and A. fasciatus.