Data from: Polyploidy and microsatellite variation in the relict tree Prunus lusitanica L.: how effective are refugia in preserving genotypic diversity of clonal taxa?

Refugia are expected to preserve genetic variation of relict taxa,
especially in polyploids, because high gene dosages could prevent genetic
erosion in small isolated populations. However, other attributes linked to
polyploidy, such as asexual reproduction, may strongly limit the levels of
genetic variability in relict populations. Here, ploidy levels and
patterns of genetic variation at nuclear microsatellite loci were analysed
in Prunus lusitanica, a polyploid species with clonal reproduction that is
considered a paradigmatic example of a Tertiary relict. Sampling in this
study considered a total of 20 populations of three subspecies: mainland
lusitanica (Iberian Peninsula and Morocco), and island azorica (Azores)
and hixa (Canary Islands and Madeira). Flow cytometry results supported an
octoploid genome for lusitanica and hixa, whereas a 16-ploid level was
inferred for azorica. Fixed heterozygosity of a few allele variants at
most microsatellite loci resulted in levels of allelic diversity much
lower than those expected for a high-order polyploid. Islands as a whole
did not contain higher levels of genetic variation (allelic or genotypic)
than mainland refuges, but island populations displayed more private
alleles and higher genotypic diversity in old volcanic areas. Patterns of
microsatellite variation were compatible with the occurrence of clonal
individuals in all but two island populations, and the incidence of
clonality within populations negatively correlated with the estimated
timing of colonization. Our results also suggest that gene flow has been
very rare among populations, and thus population growth following founder
events was apparently mediated by clonality rather than seed recruitment,
especially in mainland areas. This study extends to clonal taxa the idea
of oceanic islands as important refugia for biodiversity, since the
conditions for generation and maintenance of clonal diversity (i.e.
occasional events of sexual reproduction, mutation and/or seed
immigration) appear to have been more frequent in these enclaves than in
mainland areas.