DIFFERENCES IN SHELL PROPERTIES BETWEEN MORPHS OF LITTORARIA-PALLESCENS

Differences between the shells of the dark and the yellow morphs of the leaf-inhabiting mangrove snail Littoraria pallescens (Philippi) have been examined. In the samples studied yellows are less heavy than darks, which agrees with earlier findings that they are thinner and more easily broken. In both morphs there is a decrease in variance of shell shape between small-shelled and large-shelled individuals, and in both size classes yellows are less variable in shell shape than darks. The interpretation of these differences in relation to stabilizing selection is discussed. It is concluded that they are not simply consequences of the normal growth process but indicate the direct action of natural selection. © 1990 Kluwer Academic Publishers.