Egg proteomics of a non-invasive apple snail (Caenogastropoda, Ampullariidae) with submersed egg masses reveals unexpected investment in defensive proteins

MU, HUAWEI; HERAS, HORACIO; ITUARTE, SANTIAGO; QIU, JIAN-WEN; IP, JACK C. H.

Cambridge

Congreso; Physiomar 2017 The physiology of aquatic ectotherms in a changing world; 2017

University of Cambridge

Among gastropods, egg structure, mode of oviposition and defenses against predators or pathogens are extremely variable traits. The Ampullariidae family represents a clear example with two extreme egg laying strategies: subacuatic and aerial oviposition. While most genera deposit aquatic eggs, Pomacea and Pila lay calcareous cleidoic eggs outside the water. The evolutionary history of the egg laying strategy is unclear. The success of aerial-developing eggs has been linked to the perivitelline fluid (PVF) that surround the embryo. We have shown that its proteins, named perivitellins, provide nourishment and defenses against predators combining a warning coloration (aposematic) antinutritive, antidigestive and toxic proteins. Perivitellins have only been studied in Pomacea which contain massive stores of a non-digestible perivitellin (PV1) that provides aposematic coloration and toxic proteins, like the neurotoxin PV2 and lectins.This study analyze the divergence in the egg defensive proteins associated with the switch in the oviposition strategy. We focused on PVF proteomics of Asolene platae an ampullariid laying subaquatic eggs.Transcriptome sequencing and mass spectrometry allowed us to identify 58 proteins. Remarkably, the major defensive perivitellins of Pomacea, PV1 and PV2, were also found in Asolene eggs. We hypothesize that the original function of PV1 was nutritious and the warning coloration was acquired later, associated with the acquision of defenses. The function of PV2 is still unclear, but, as it is composed by perforin and lectin subunits of recognized immune function, they could play this role, and later be combined into a single neurotoxic protein in above-the-water eggs. Another feature is the presence of several immune-related proteins, some not found in Pomacea. The greater investment in immune proteins in Asolene compared with Pomacea snails, may be related to the higher fowling potential to which gelatinous eggs are exposed to. Overall it seems that, contrary to previous hypotheses, the nutritious and defensive perivitellins are ancient molecules previous to the acquisition of the above-the-water eggs.