The eggs of the apple snail <i>Pomacea maculata</i> are defended by indigestible polysaccharides and toxic proteins

Abstract

The freshwater snails Pomacea lay conspicuous aerial eggs clutches that are ignored by most predators. Egg biochemical defenses in the apple snail P. canaliculata (Lamarck, 1822) are provided by multifunctional proteins. We analyzed the eggs of a sympatric species, P. maculata Perry,1810, studying the gross composition, toxicity, hemagglutinating activity, as well as its antinutritive and antidigestive properties. Eggs are mostly composed of polysaccharides, mainly galactogen, and proteins, followed by lipids and non-soluble calcium. Two perivitellins account for ∼85 % dw of the egg protein. The major lipids are phospholipids and sterols. A suite of potential defenses were determined, including strong lethal neurotoxicity on mice and moderate antidigestive and lectin activities. Remarkably, their polysaccharides were refractive to in vitro digestion by digestive glycosidases. This study characterized ∼99% of egg composition and identified multiple potential defenses, provided not only by proteins but also polysaccharides. This is the first evidence to our knowledge that reserve sugars may be involved in defenses, giving further insight into the unusual reproductive strategy of these well defended snail eggs.