Biochemical defenses against predation of apple snail eggs resemble plant strategies against herbivory

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

Quebec

Congreso; Physiomar 10; 2010

Work has thoroughly established that the eggs of most animals are subject to intense predation. Among the few exceptions are the aerial egg clutches from the aquatic snail Pomacea canaliculata which have virtually no predators. Its defenses are advertised by the pigmented ovorubin perivitellin providing a conspicuous reddish coloration, but the nature of the noxious defense was unclear, except a screening for defenses that identified a neurotoxic perivitellin with lethal effect on rodents. Ovorubin is a proteinase inhibitor (PI) whose role to protect against pathogens was taken for granted, according to the prevailing assumption. Through a combination of biochemical, biophysical and feeding experiments we studied the proteinase inhibitor function of ovorubin in egg defenses. We found that ovorubin PI belongs to the small Kunitz type serine proteinase inhibitor family and specifically binds and blocks trypsin from mammals. In contrast to the classical assumption, neither ovorubin nor other egg components prevents bacterial growth. Ovorubin antitrypsin activity was found extremely resistant to in vitro gastrointestinal proteolysis. Moreover feeding studies showed that ovorubin ingestion diminishes growth rate in rats indicating that this highly stable PI is capable of surviving passage through the gastrointestinal tract in a biologically active form. This is the first direct evidence of the interaction of an egg PI with a digestive protease of potential predators, limiting predator’s ability to digest egg nutrients. This role has not been reported in the animal kingdom but it is similar to plant defenses against herbivory, opening new perspectives in the study of the evolution and ecology of mollusk defensive strategies.