Genetic diversity and spatial structure of the imperiled European population of Malus trilobata in Greece

Abstract

Malus trilobata, is a rare tree species occurring in several small and disjunct populations in the eastern part of the Mediterranean basin. The main European population is found in the region of Evros (NE Greece) and is divided in five distinct subpopulations following the species geographical pattern. The genetic diversity of approximately the entire population (69 trees) was analyzed using nuclear microsatellite and random genomic markers. Polymorphism was discovered in 29 out of 45 genomic marker loci (64.44%), while for nuclear microsatellite markers, all three loci were polymorphic with an average of 3.75 alleles per locus. Our results unraveled a specific grouping pattern for both markers. Both genetic markers exhibited relatively low genetic diversity which is in accordance with the prevalent perception that species with fragmented distributions tend to have low genetic diversity, while the differentiation among individuals, revealed a patchy pattern among small groups of trees separated by roads, firebreaks or distance. These results indicate a high genetic fragmentation level for the main European population of M. trilobata, while the presence of roads, firebreaks, conifer plantations and agricultural land, seem to function as potential barriers to gene flow. Consequently, and since it is well-documented that bees hesitate to change foraging patches, as long as their food is abundant, the observed genetic differentiation patterns could be partially attributed to the foraging and flight behavior of bees, which are the main pollinators of the species. The low levels of available genetic diversity combined with the small overall population and repeated events of forest fires inside the M. trilobata distribution, perils the survival of the species and imposes the necessity for a thoroughly organized conservation strategy.