Data from: High genetic diversity and distinctiveness of rear-edge climate relicts maintained by ancient tetraploidisation for Alnus glutinosa

Populations located at the rear-edge of a species’ distribution may have
disproportionate ecological and evolutionary importance for biodiversity
conservation in a changing global environment. Yet genetic studies of such
populations remain rare. This study investigates the evolutionary history
of North-African low latitude marginal populations of Alnus glutinosa
Gaertn., a European tree species that plays a significant ecological role
as a keystone of riparian ecosystems. We genotyped 551 adults from 19
populations located across North Africa at 12 microsatellite loci and
applied a coalescent-based simulation approach to reconstruct the
demographic and evolutionary history of these populations. Surprisingly,
Moroccan trees were tetraploids demonstrating a strong distinctiveness of
these populations within a species otherwise known as diploid.
Best-fitting models of demographic reconstruction revealed the relict
nature of Moroccan populations that were found to have withstood past
climate change events and to be much older than Algerian and Tunisian
populations. This study highlights the complex demographic history that
can be encountered in rear-edge distribution margins that here consist of
both old stable climate relict and more recent populations, distinctively
diverse genetically both quantitatively and qualitatively. We emphasize
the high evolutionary and conservation value of marginal rear-edge
populations of a keystone riparian species in the context of on-going
climate change in the Mediterranean region.