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

Abstract

In 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 aposematic coloration must have evolved without kin-selection.

Factors promoting marine invasions: A chemoecological approach

“…From the viscera of S. geographica we isolated the known bioactive flavonoids apigenin (5), genkwanin (6), and chrisoeriol (7) (Fig. 2) (27)(28)(29)(30).…”

“…1-5 and references therein). Chemical defense is now understood as the driving force behind the evolution of the group, preceding the regression of the shell and the abandonment of mechanical defense (6)(7)(8)(9). Adaptive radiation, with switches from one chemically defended food source to another, has been documented by means of comparative techniques.…”

Chemical Defenses: From Compounds to Communities

“…Nudibranch evolution is thought to be closely tied to the use of chemical defenses because nudibranchs have lost the physical defense of a shell (Faulkner and Ghiselin, 1983). Surprisingly, the compounds found in phyllidiid nudibranchs have rarely been tested as fish feeding deterrents even though these opisthobranchs are conspicuously colored and are diurnal.…”

Chemical Defenses of Cryptic and Aposematic Gastropterid Molluscs Feeding on their Host Sponge Dysidea granulosa

“…Many traits that drive the evolution of opisthobranchs, such as shell reduction or loss, have resulted from coevolution with diet organisms (Faulkner and Ghiselin, 1983;Ghiselin, 1998,1999;Cimino et al, , 2001). Without shells, many opisthobranchs rely on other defense mechanisms.…”

“…Aposematic or warning coloration is at the opposite extreme, and evolutionary theory postulates that aposematic coloration evolves in deterrent species because it is a more effective warning signal than the alternate cryptic coloration (Wallace, 1867;Poulton, 1890). In opisthobranchs molluscs, warning coloration is based on the benefits provided by chemical defenses often sequestered from the opisthobranch food source (Faulkner and Ghiselin, 1983;Avila, 1995), and it seems associated with evolutionarily more derived, rather than more basal, taxa (Gosliner, 2001). …”