Effects of trophic availability on the shell morphology of the apple snail Pomacea canaliculata

TAMBURI, NICOLÁS EDUARDO.

Rio de Janeiro

Congreso; XI International congress on medical and applied malacology (XI ICMAM); 2012

SOCIEDAD INTERNACIONAL DE MALACOLOGIA MEDICA Y APLICADA

Pomacea canaliculata is a freshwater snail native from South America and a successful invader worldwide. The shell shape on this genus is highly variable leading to considerable taxonomic confusion. It has been previously determined that the origin of interpopulation variation is both genetic and environmental but the reaction norms to specific environmental factors such as trophic availability are still unknown. The aim of our study was to search for shape changes attributable to the food availability at which snails were reared. Eighty two full sibling snails were reared individually, under seven different levels of fresh lettuce availability (from 100% to 20% of ad libitum ingestion rate). The shells were photographed in apertural view at maturity (one month after the first egg mass) and we analyzed nine landmarks and ten semilandmarks using geometric morphometrics techniques. In males and females significant allometry was found: a relative decrease of the spire height in both sexes and an expansion of the shell aperture in males. Due to this sexual dimorphism males and females were analyzed separately and thereafter we worked with the residuals of the regression between shape and size (centroid size) to remove the allometric component. We found a significant relationship between shape and trophic availability in females, being more globose and with a higher aperture when grown at high food availability levels. In the case of males, no relationship between shape and food availability was found after removal of the allometric effect; this could be due to the absence of this relationship or to the high correlation between food availability and size at maturity (males mature always at the same age but at different sizes). The morphological differences found between females relative to trophic availability could be useful for paleoenvironmental reconstruction and for assessment of actual trophic availabilities in the field.