Chemical defense and evolutionary ecology of dorid nudibranchs and some other opisthobranch gastropods

Abstract

the evolution of dorid nudibranchs and some other opisthobranch gastropods loss of the shell is correlated with the presence of defense mechanisms based upon chemicals derived from food. The chemicals are present as the result of adaptations, not by accident. Chemical defenses were preadaptive, enabling the animals to dispense with the shell. They have been gradually elaborated and made more effective, occasionally leading to de novo synthesis, independent of diet. Food dependencies have constrained the adaptive radiation of oplsthobranchs, and this may reflect relatlonshlps to predators as well as prey. For the opisthobranchs considered here, distastefulness is often combined with conspicuousness (aposematic coloration): since these animals do not occur in family groups, the