Understanding long-distance seed dispersal by sea currents: first results of experi ments on Juniperus, Daucus, Ferula and Pancratium spp. from the Mediterranean Basin

To increase their evolutionary success, plants developed several adaptations to spread as widely and quickly as possible. Among them, the dispersal by water or hydrochory is a widely recognized but often overlooked effective syndrome; if propagules are also saltwater resistant, these can be dispersed through sea currents and break the barriers of insularity. The Mediterranean Basin, and especially islands, are natural laboratories of sea hydrochory (thalassochory) as main or complementary syndrome. We performed experiments with dispersal units of four genera native to the Mediterranean (Juniperus, Daucus, Ferula and Pancratium) including species differing in their distribution and possible dispersal ability: the coastal Juniperus macrocarpa, Daucus rouyi, Ferula arrigonii and Pancratium maritimum vs. the preferably inland J. turbinata and J. oxycedrus, F. communis and D. carota; and the endemic inland P. illyricum. We tested their period of dispersal units’ buoyancy and seed viability after floating to hypothesize their colonization distances. Our preliminary results suggest that some species show specific thalassochory syndrome while others could be dispersed by sea, although they probably evolved primarily for other dispersal types. Pancratium maritimum shows synchrony in floatability and vitality, suggesting a strong interconnection between the two traits. The congeneric P. illyricum shows poor floating ability and resistance to saltwater, which might explain its limited distribution. The genera Daucus and Ferula showed as well poor floating ability, but they can germinate after seawater exposition. Differently, all Juniperus species –all spread through insular and continental Mediterranean territories– show a less floatability than P. maritimum, while their viability remains high even after sinking, confirming that Juniperus species are particularly adapted to other dispersal types, such as endozoochory, although they are occasionally or stochastically able to be long dispersed by sea. This study contributes to explaining the overlooked but potentially crucial ability of vascular plants to colonize Mediterranean coastal ecosystems.