Colour polymorphism in idotea baltica from the Bay of Naples and its ecological significance

Abstract

In order to elucidate the ecological significance of polychromatism in Idotea baltica (Crustacea: Isopoda), the distribution of the various phenotypes was studied for three consecutive years in a population from the Bay of Naples. The most abundant morphs were uniformis (males: 394%-100%; females: 24·6%-84·1%) and maculata (males: 0·59·8%; females: 0%·50%), their distribution varying throughout the year. The assessment of some biological characters (females size, fecundity and embryonic stages of development) did not show any differences accounting for preferential fitness of these phenotypes. Moreover, it was observed that phenotypic diversity in colour morphs followed seasonal changes in the substrate composition. In agreement with other investigators, it has been suggested that the camouflage function of polychromatism may have a fundamental role in the reduction of predation, and favour Idotea baltica colonizing a variety of changeable habitats.