Dispersal capability often decides the geographical distribution and long-term success of a species.In this investigation, Pontodrilus litoralis, a widely distributed species along shores throughout mid- and low latitudes of the world, was investigated.We tested three hypotheses explaining its dispersal: helped by humans, transported by birds and carried by currents.Although the earthworms seemed to be associated with artificially planted wind-breaking woods and mangroves along the west coast of Taiwan, they were also found on isolated beaches in the Pescadores Islands without such plantings.They are approximately 2 Fab Parts mm wide, making them too small for use as fishing bait.
These two mechanisms invoking human help were not supported.In a laboratory experiment, we moved the earthworms to the plumage of various body parts of pigeons, and they dropped off or died within a short time, a result incompatible with the bird hypothesis.The earthworms stayed alive and grew when immersed in freshwater or seawater for at least a month.They also survived on floating wood in an in situ experiment lasting approximately two months.Thus, the current hypothesis was the only one we were unable to falsify; driftwood and perhaps wooden vessels could provide both food and transport on long journeys.
Wood boats exist for a short time on an evolutionary time scale, but it may be long enough to disperse the Haircut Kits earthworm around the world.The phase-out of wood boats, thus, may start the divergence of P.litoralis populations around the world.