Study on the presence of chemical defense against predators in the early stages of the Opisthobranch Aplysia depilans

Abstract

The existence of efficient chemical defenses used by Opistobranchs to get protection from predator’s attacks is already established. However, little is known about the defenses in the early life stages of these animals. Predation on eggs, recruits and juveniles can be very important since these stages are almost sessile, and have no physical protections like shells. Few predator species were reported feeding on Aplysia egg masses or juveniles, this may let someone ask about the origin of the deterrence of these early life stages. The deterrence of three developmental stages of the egg masses and two sizes of the juveniles of Aplysia depilans were tested against the sympatric predators. Anemonia sulcata and Carcinus aestuarii. Extractions and artificial diets made with the extracts were used to test the chemical origin of the defenses. The egg masses and the juveniles of Aplysia depilans were deterrent to Anemonia sulcata and Carcinus aetuarii and the defense seems to be chemically mediated. The three groups of eggs were deterrent to both of the predators tested (p<0.05). The deterrence was chemically mediated as the predators eat the extracted eggs and the two predators tested rejected the artificial diets where the extracts were incorporated. Juveniles but not recruits were deterrent to Anemonia sulcata. And both sizes of the juveniles were rejected by the crabs, the artificial diets made with the extracts from the juveniles repelled eating from both of the predators tested.