Egg cannibalism in pomacea canaliculata (caenogastropoda, ampullariidae) from Southern Pampas: an alternative trophic strategy?

Abstract

Pomacea canaliculata is a freshwater gastropod native to southern South America and is listed among the world?s 100 worst invaders. Diverse food sources can be exploited by this apple snail, including snails with gelatinous and subaquatic egg masses. Records of ingestion of their own egg masses (egg cannibalism), which are aerial and calcareous, have only been anecdotal in P. canaliculata. Our aims were to study egg cannibalism in a natural population and also under laboratory conditions. In a stream population from Southern Pampas we recorded P. canaliculata attacking their own fresh egg masses which had been naturally submerged by an increase in water level. In addition, when we artificially submerged fresh and old egg masses in a field experiment, we observed several snails readily attacking both. In the laboratory we also observed the capture by pedal surface collecting of floating remains of egg masses. In laboratory trials juveniles fed on eggs reached larger sizes than starved snails but smaller than those fed on lettuce; adult snails also eat eggs but their growth rates were not affected by the food regime. Pomacea canaliculata eggs present defensive and anti-nutritive compounds that apparently dissuade almost all potential predators, but this snail did not appear to be negatively affected when feeds on its own eggs. The ingestion of egg remains and submerged egg masses is probably more frequent than previously considered in P. canaliculata, which may take advantage of using these alternative food resources when others are scarce.