Ontogenetic and intersexual variations of ciliary feeding in the freshwater snail Pomacea canaliculata

SAVEANU, L. Y MARTÍN, P. R.

San Miguel de Tucumán, Tucumán

Workshop; 4th International workshop on the Biology of Ampullariidae; 2010

Ciliary feeding is one of the alternative trophic mechanisms of Pomacea canaliculata, an invasive snail mostly known by its capacity to ingest vigorous vascular plants. Through this mechanism, particles and biofilms are collected from the water surface by ciliary action of the foot, which forms a funnel with its anterior part, and remains attached to the substratum with its posterior part. The aim of this study was to determine the existence of ontogenetic and intersexual variations of ciliary feeding. Snails from the Guaminí stream (Buenos Aires, Argentina) and their hatchlings obtained in laboratory were kept at 25 ºC and fed on lettuce. In this study, 116 individual observation trials were performed in plastic aquaria (35 cm diameter) with snails of different sizes (2.7 to 52.8 mm) and sex. Fish food flakes were scattered on the water surface and the snails’ activities were chronometered for two hours. Morphometric variables of the pedal funnel were recorded on digital images and the amount of food caught was estimated from the remaining food. Ninety two percent of the snails bigger than 20mm performed ciliary feeding, while only 61.9% of those smaller than 20 mm did it. Only snails smaller than 20 mm performed crawling and feeding on the surface without forming a funnel (33.3% of the cases), combined or not with ciliary feeding. Funnel perimeter and area grew with negative allometry relative to shell length. The total amount of food captured in two hours increased and the specific capture rate (captured food per unit time relative to the snail live weight) decreased with shell length. Time spent on ciliary feeding showed a slight tendency to increase relative to shell length while the number of ciliary feeding events and funnels showed no trend. Intersexual differences were not found for any of the variables studied. As a final result, an increase in size represents an increase in the amount of food caught, and therefore, if this take place in the field, the effect on the water body could be more aggressive by big snails than by small. The specific capture rate obtained by ciliary feeding was lower than by surface crawling and feeding, but this last mechanism can only be used by snails smaller than 20mm. This difference could be explained by the constant food availability that the snail encounters when it crawls under unexploited areas, in contrast with ciliary feeding in which low density areas are generated around the funnel and which are not replenished immediately by particles. In addition, qualitative observations were conducted in collective 24 L aquaria with different food resources potentially found in natural environments. Snails from 8.6 mm to 48.6 mm were able to capture and ingest materials as diverse as panicles of grasses (Cortaderia selloana), biofilms, etc.