Intercontinental long‐distance seed dispersal across the Mediterranean Basin explains population genetic structure of a bird‐dispersed shrub

Long-distance dispersal (LDD) is a pivotal process for plants determining
their range of distribution and promoting gene flow among distant
populations. Most fleshy-fruited species rely on frugivorous vertebrates
to disperse their seeds across the landscape. While LDD events are
difficult to record, a few ecological studies have shown that birds move a
sizeable number of ingested seeds across geographic barriers, such as sea
straits. The foraging movements of migrant frugivores across distant
populations, including those separated by geographic barriers, creates a
constant flow of propagules that in turn shapes the spatial distributions
of the genetic variation in populations. Here, we have analysed the
genetic diversity and structure of 74 populations of Pistacia lentiscus, a
fleshy-fruited shrub widely distributed in the Mediterranean Basin, to
elucidate whether the Mediterranean Sea acts as a geographic barrier or
alternatively whether migratory frugivorous birds promote gene flow among
populations located on both sides of the sea. Our results show reduced
genetic distances among populations, including intercontinental
populations, and they show a significant genetic structure across an
eastern-western axis. These findings are consistent with known bird
migratory routes that connect the European and African continents
following a north-southwards direction during the fruiting season of many
fleshy-fruited plants. Further, Approximate Bayesian Analysis failed to
explain the observed patterns as a result of historical population
migrations at the end of Last Glacial Maximum. Therefore, anthropic and/or
climatic changes that would disrupt the migratory routes of frugivorous
birds might have genetic consequences for the plant species they feed
upon.