Gastropodochory 2.0: Slugs and snails disperse plant seeds, ferns, mosses and lichens - recent findings of what began in 1934

Background/Question/Methods

When slug feeding traces on fleshy fruits in forests caught the attention of the Swiss botanist Paul Müller-Schneider, he hypothesized that gastropods may aid endozoochorous seed dispersal in these plants. Subsequent experiments confirmed his assumption and were published in 1934. This phenomenon of gastropod seed dispersal he named gastropodochory. Sixty-four years later, similar findings were made in the Pacific Northwest. Recently, we provided evidence derived from several studies of gastropods dispersing vascular plants, ferns, mosses and lichens. In general, gastropods consume seeds and also spores of ferns and bryophytes as well as lichen fragments and defecate them mostly intact and germinable. For myrmecochores or ant-dispersed plants we found gastropods to ingest seeds of a number of species, under laboratory as well as field conditions. Our estimated dispersal distance of seeds by large slugs in forests averaged 5 m, exceeding the mean dispersal distance by ants which is often less than 1 m. Gastropod species and size and also the seed type and size matter in quantifying the dispersal potential of gastropods. In agricultural landscapes a number of weeds lack obvious dispersal structures, and mechanisms of non-human dispersal are often unknown. We investigated whether gastropods could facilitate dispersal of weeds and results supported our expectations. Even aquatic invasive apple snails fed on seeds of weeds from irrigated rice fields in the Philippines and defecated them viable.

Results/Conclusions

Seed dispersal distances of forest myrmecochores by slugs matched well with migration rates observed in other studies, raising the question on how important gastropods are in herb migration. Gastropods even bear the potential to substitute ants as seed dispersers in certain habitats where ants are rare but myrmecochores are abundant as is the case in many European beech forests. In addition, native large slugs are outcompeted by the invasive Spanish slug in Central Europe and we found indications that the invasive slug - in contrast to its native relatives - destroys a fair amount of seeds in its guts. Given the many gastropod invasions worldwide, these mollusks might have altered existing dispersal mutualisms of plants and native ants, gastropods or other animals unperceived. In the agri-environment, gastropod seed dispersal might describe weed movement or it might be of importance in the approach to re-establish plant diversity in organic farming. The recent findings of gastropods dispersing a variety of plants demonstrate that this phenomenon was overlooked for many years and requires more research.