Pomacea canaliculata perivitellins. Storage proteins or defensive molecules?

HERAS, H.; ITUARTE,S.; FRASSA,V.; DREON, M.S.

Tucumán

Workshop; IV International workshop on the biology of Ampullariidae; 2010

INIBIOLP

Decades of fieldwork have thoroughly established that the eggs of most animals are subject to intense predation. The reason is clear: Their high nutritional value presents to a pest or pathogen the best target for attack. Among the few exceptions are the eggs from the freshwater apple snail Pomacea canaliculata which, though filled with large amounts of polysaccharides and storage proteins (perivitellins), have only one predator reported: the fire ant Solenopsis geminate. Work in the last decade have demonstrated that these perivitellins have other biological activities besides being storage proteins, among them is their role to advertise egg defenses by the pigmented perivitellin ovorubin, providing a conspicuous reddish coloration (aposematic). Recently, we have also demonstrated that another storage protein, PV2 is a neurotoxic perivitellin with strong lethal effect on central nervous system of rodents. Further, ovorubin is a proteinase inhibitor that interacts with the digestive protease of potential predators, limiting predator´s ability to digest egg nutrients. This role has not been reported in animals but it is similar to plant defenses against herbivory. This would be the only defense model with no trade-offs between conspicuousness and noxiousness by encoding into the same molecule both the aposematic warning signal and an antinutritive/antidigestive defense. The evidence gathered therefore indicates that egg’s multifunctional perivitellins are not only storage proteins providing nutrients for the embryo, but also a suite of defenses composed of antinutritive/antidigestive, neurotoxic and aposematic components. This biochemical defenses, probably combined with unpalatable factors would explain the near absence of predators and also the behavior of the snail kite (Rostrhamus sociabilis) that invariably discard the albumen gland (site of perivitellin synthesis) when predating on female P. canaliculata. These defensive/storage proteins acting simultaneously would impair the acquisition of nutrients and toxify the predator thus rendering P. canaliculata eggs unusually well defended opening new perspectives in the study of the evolution and ecology of egg defensive strategies.