Ingestion of poisonous eggs from the invasive apple snail Pomacea canaliculata adversely affects bullfrog Lithobathes catesbeianus intestine morphophysiology

The poisonous eggs of Pomacea canaliculata (Caenogastropoda, Ampullariidae) hardly have any predator. This invasive snail, listed among the 100 worst invasive species, is a serious crop pest and a vector of a human parasitosis. Females lay eggs in pink-reddish masses, presumably as a warning coloration of their chemical defenses. Egg ingestion alters rodents gastrointestinal tract and is lethal if injected, but its effect on other taxa is unknown. Here we explored the toxic effects of Pomacea canaliculata eggs on bullfrog Lithobathes catesbeianus (Anura, Ranidae). Juvenile bullfrogs were gavaged with egg extracts and their digestive tract analyzed after 24 h and 48 h using histological, immunohistochemical and lectin-histochemical techniques. Toxicity was also evaluated by intraperitoneal injection of eggs extracts. Egg extract ingestion adversely affected small intestine of bullfrogs. Short term (24 h) effects included large, reversible changes of the intestinal wall, villi morphology, and changes in the glycosylation patterns of enterocytes. The mucosal area increased and infiltration of inflammatory cells, mainly eosinophils and macrophages, were observed together with a weak hemorrhage. Most of these changes reversed after 48 h. Besides, intraperitoneal injection of egg extract was nontoxic to bullfrog juveniles and no lethality or behavioral changes were observed, a remarkable difference with eggs effect on mammals. As a whole, these results indicate that toxins of apple snail eggs reversibly modify gut morphology, which may alter bullfrog physiology limiting their ability to absorb egg nutrients. This study extends the known targets of the apple snail egg defenses against predation to amphibians.