Population genetic structure and conservation of the Azorean tree Prunus azorica (Rosaceae)

Prunus azorica is an endangered tree endemic to the Azores Archipelago, considered as a top priority species for conservation. Although propagation measures have been studied in detail, and a broad phylogeographic study on P. lusitanica was recently published, a detailed population genetics study devoted to Azorean taxon was lacking. To determine extant patterns of population genetic structure in P. azorica, we analysed eight populations from the five Azorean islands where the species presently occurs and the only extant individual from Flores Island. We also included samples of P. lusitanica subsp. hixa from the Canary Islands and Madeira, and of P. lusitanica subsp. lusitanica from mainland Portugal. Genotyping was undertaken for eight nuclear microsatellite polymorphic loci specifically isolated for P. azorica. Accessions of the different geographic regions were used to sequence ITS and trnL DNA regions. Regarding SSRs, the number of alleles ranged from 5 to 37 (mean = 12.6) per locus and from 2 to 64 per population (mean = 24). Our analysis showed a clear separation between samples from the Azores and those from other regions. Overall, São Miguel populations seemed to encompass the majority of the variability found within the archipelago. Regarding the Azorean populations only, the highest percentage of genetic variation was found within populations (92 %). Still, about 7 % of the variation was found among populations within islands. Expected heterozygosity ranged from values near 0 in the most depauperate populations up to 0.18. With a few exceptions, the level of differentiation between Azorean populations was generally low and gene flow was clearly above 1. Analysis of ITS sequences also detected differences between the Azores and the remaining regions but the trnL region did not reveal any variation. The genetic identity of P. azorica was recognised and thus should be preserved; however, the present results suggest that the Azorean taxon should be reinstated at the subspecies level.