Snails chat chemically about food availability

Slow moving animals, like snails, pay a high price for moving the wrong way. If they send each other information about the best choice via chemical signals, they could optimize their movement decisions considerably.

Photograph of the great pond snail Lymnaea stagnalis grazing on a freshwater algal biofilm; photo credit: Dr. Lars Peters, www.blueseapictures.de

For herbivores in general, but in particular for those with limited motility such as gastropods, the search for food is risky and cost-intensive. On the other hand, it is obviously a vital requirement for the maintenance of the herbivores’ fitness. Since energy gain depends not only on food availability, but also on the nutritional quality of the food, consumers should be able to differentiate between spatially and temporally variable resource items. For consumers, it appears to be highly adaptive to utilize environmental chemical cues to convey information about a diet’s quality over a certain distance. Such a strategy mediated by chemical signal substances would clearly help the consumers to optimize their movement decisions within their environment. In two recent publications, we had already demonstrated that freshwater snails are able to differentiate between high- and low-quality food sources, only by the perception of food odours (volatile infochemicals, Moelzner & Fink 2014, doi 10.1111/1365-2656.12220) and that grazing of conspecific snails causes an aggregation of grazers under natural conditions (Moelzner & Fink 2015, doi 10.1890/ES14-00246.1). The piece of evidence that was missing however was whether the grazing activity of snails actually causes the liberation of chemical cues that could evoke the aggregation behaviour in their conspecifics and whether this mechanism could operate at environmentally reasonable cue concentrations. In our new paper “Gastropod grazing on a benthic alga leads to liberation of food-finding infochemicals”, we found that the grazing activity of pond snails (Lymnaea stagnalis, see picture) on algal biofilms causes the liberation of the same bouquet of chemical signal substances that had previously been demonstrated to cause aggregation behaviour in this species. We were able to determine the threshold concentration required for the snails’ behavioural response and related this to an environmentally realistic scenario of biofilm-grazing snails that – through their grazing activity – send information about the quantity and quality of available resources (algal biofilms) to their conspecifics in the surroundings. In summary, the emission of chemical cues through snail grazing with subsequent attraction of other snails to algal biofilms indicates an important but so far understudied chemical signalling mechanism of ecological importance in lakes and streams.