Pigmented corpuscles in the midgut gland of Pomacea canaliculata and other Neotropical apple-snails (Prosobranchia, Ampullariidae): A possible symbiotic association.

CASTRO-VÁZQUEZ A, ALBRECHT EA, VEGA IA, KOCH E, GAMARRA-LUQUES C.

BIOCELL

INCA

Lugar: MENDOZA; Año: 2002 vol. 26 p. 101 - 109

0327-9545

ABSTRACT: Excretory function has been attributed to the pigmented corpuscles in the midgut gland of ampullariids for decades (Meenakshi, 1955; Andrews, 1965; Lutfy & Demian, 1968). However, we have reviewed here the evidence suggesting the symbiotic nature of the “spherioles” present in P. canaliculata and other Neotropical Ampullariidae. The emerging picture suggests that C corpuscles are indeed the vegetative forms of a prokaryotic symbiont inhabiting the columnar cells of the midgut gland alveoli. The possibility that K corpuscles were the kystic forms of the same organism should also be considered. We compare symbiotic associations of opistobranch mollusks (midgut gland) with either algal cells and chloroplasts and putative symbiotic association described here. Because of the size of C corpuscles and their location in the midgut gland cells of P. canaliculata, is reminds somehow this case with that.The putative symbiotic elements (C corpuscles) have been found in all P. canaliculata individuals that we have sampled so far, so we believe that they are a normal constituent of the midgut gland of this species. Therefore, one may wonder which might be the physiological advantage (for the apple-snail) of carrying a lodger that occupies a significant part of its most voluminous organ, and which causes significant fecal losses of nitrogen and carbon. In general, the benefits reaped by mollusks that live in symbiotic associations are nutritional ones, and therefore, it is reasonable to hypothesize that ampullariids may compensate for the nitrogen and carbon losses through some unknown nutritional advantage. An interesting possibility that should be explored is that the current association was a chemosymbiosis that would take advantage of the usually high sulfide content of sediments where these snails live. Such chemoautotrophic associations have been described in deep sea mollusks that live in sulfide-rich hydrothermal vent environments.