Pomacea canaliculata eggs are defended against frog predation by altering their small intestine morphophysiology

BROLA, TABATA ROMINA; HERAS, HORACIO; FERNÁNDEZ, PATRICIA ELENA; DREON, MARCOS SEBASTIÁN

Buenos Aires

Congreso; XLVII Reunión Anual SAB; 2018

Pomacea (Caenogasteropoda: Ampullariidae) fresh water snails are native from south America and have been introduced in different parts of the world where they cause serious economic losses. They are also human disease vectors as the human eosinophilic meningoencefalitis. These snails lay their eggs above water thus exposing them to environmental stressors. Remarkably, they have no reported predators although their aerial oviposition strategy exposes them to terrestrial predation. Recent studies have shown that the perivitelline fluid (PVF) that surrounds the embryo, besides nourishes them, contains a cocktail of lectins, neurotoxins, protease inhibitors and antinutritive proteins involved in a unique defence system against predation. Strikingly this defence system is quite similar to the one thoroughly studied for plants against herbivorous animals but has not been previuosly described in animals except for Pomacea genus. These PVF proteins, hereafter perivitellins, are massively stored in the egg. In previous works we demonstrated they resist extreme pH conditions and digestive proteases degradation, withstanding the passage through the gastrointestinal tract of rodents and simultaneously affecting their gut morpho-physiology. So far, these effects have been only tested in mammal models yet there is still no information whether this antidigestive perivitellins have some nutritional implicances in other animals. In this work we evaluate the antinutritve and antidigestive properties of the perivitellins of P. canaliculata in Lithobathes catesbeianus as an amphibian model and potential predator of the eggs. We orally administrated the PVF to sexually immature frogs and animals were euthanized 24h and 48h after treatment. The anterior part of the small intestine was analysed by haematoxylin and eosin stain for general structure. To identify changes in enterocytes glycosylation patterns, lectin-histochemistry with seven different lectins was performed. Eosinophils were counted, and the presence of macrophages was determined using CD68 monoclonal antibodies. Immunohistochemistry using antiPV2 polyclonal antibodies was performed. Morphological parameters of the gut villi were also analyzed. Perivitellins of P. canaliculata seems to drastically modify the villi morphology of the small intestine of frogs altering their width and length and decreasing its absorptive surface area when compared to control group. A great increase of the connective tissue of the villi is observed as well as an increase in the number of inflammatory cells, specially eosinophils and macrophages. Surprisingly, these cells not only appear in the corium of the villi but also within the gut epithelium. The gut epithelium is strongly marked with antiPV2 polyclonal antibodies while enterocytes glycocalyx is also altered as shown by lectin-histochemistry. This meaning that proteins are somehow attached to the enterocytes which might cause these abnormal morpho-physiological effects.The results of this study show that P. canaliculata PVF has a strong effect on the digestive properties of the frog. Considering that this has also been previously demonstrated for rodents and that the PVF is known to contain antinutritive proteins, protease inhibitors and lectins it is possible that the PVF is involved in an antipredator system by lowering the nutritional value of the eggs and altering the normal functioning of the digestive system thus preventing from using the available resources in the egg