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Trophic flexibility is a relevant trait in the potential for organisms to establish widely, maintain high abundances and spread after invasion. Pomacea canaliculata is an apple snail that feeds primarily on aquatic macrophytes, although it also consumes other trophic resources that likely play an important role in its persistence and contribute to its effects in invaded wetlands. In the present study we determined the ingestion rates in P. canaliculata for carrion and subsequent effects on growth, and performed field and laboratory experiments to investigate the mechanism of carrion detection. We observed P. canaliculata snails of all sizes feeding on carrion. The specific ingestion rates of carrion decreased with snail size and were 20 times lower than when feeding on lettuce. The growth rates of snails feeding only on carrion were 15–30% higher than those of fasting snails and 30% of those snails feeding on lettuce or lettuce and carrion. We found no evidence of distant chemoreception of carrion. The importance of carrion for P. canaliculata is mostly as an alternative resource when its preferred food is absent, and not as a complementary resource that could enhance growth. Nevertheless, the ability of P. canaliculata to profit from carrion may help explain its potential to establish widely and to have effects on aquatic vegetation.

Lithic particles are a common feature in the digestive tract of freshwater snails. Their role in the digestive processes has been demonstrated in some microphytophagous and detritivorous species, as they enhance growth, assimilation and reproduction. It has been suggested that they could have the same function in Pomacea canaliculata, a macrophytophagous apple snail with powerful jaws and radula, a strongly muscular and cuticularized gizzard and high levels of enzymatic activity. Our aims were to investigate the occurrence of lithic elements in the digestive tract of P. canaliculata snails from natural populations through the analyses of digestive contents, as well as the effect of size and availability of lithic particles on growth and growth efficiency through laboratory experiments. Lithic particles are very common in the digestive tract of P. canaliculata from natural populations and from laboratory aquaria if they are available in the immediate environment. Such particles are not retained or concentrated differentially in the stomach and they are apparently totally lost in less than four weeks if the supply is interrupted. The frequency of plant material and lithic particles increases from mouth to anus indicating that the retention time increases in the same way. Sand and plant material frequently co-occur in the intestine and in the stomach indicating that both are ingested together. Ground marble had negative effects on the growth of P. canaliculata probably due to the sharp edges and pointed ends of these particles. The availability of natural lithic particles (sand) had a positive effect on growth and also a synergic interaction with the availability of food. The growth efficiency was 25.2% higher when sand was available than when it was absent. These effects were more marked in juvenile females than in juvenile males. Our results indicate that growth rates may be underestimated under laboratory conditions if lithic particles are not supplied regularly and that their presence should be standardized to allow reliable comparisons between studies. Our results also indicate that the effects of food availability and plant palatability on the growth of P. canaliculata may be modulated by the presence of lithic particles and this may in turn affect the outcome of interactions between apple snails, other snails and macrophytes.

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