Abstract
Microsatellite markers were used to characterize the structure of genetic diversity in natural Moroccan Aleppo pine (Pinus halepensis Mill.) populations, the most southwesterly marginal populations of the species in the Mediterranean Basin. Twenty-two natural populations and one artificial population, located in four regions covering most of the natural range of P. halepensis in the country, were sampled. Across this range, towards the south and west (and towards high altitudes) the populations become increasingly discrete and discontinuous. The nuclear microsatellite marker analysis suggests that a large proportion of the Aleppo pines in Morocco have derived from a single genetic lineage, represented by a central group of 11 of the examined populations located in the High and Middle Atlas Mountains. In addition, two smaller groups, represented by the marginal southwestern High Atlas populations, and three still smaller north / northeastern groups of populations located in the Rif and northeast Middle Atlas Mountains, could be genetically distinguished. Further, coalescence analysis of historical demographic population patterns suggests that ancient bottlenecks occurred in all of the natural populations. However, the population differentiation and genetic diversity levels we found were good (F(st) =15.47), presumably because of the species' good potential for long-distance dispersal of seeds and high invasive capacity, which appear to have maintained a state of stable near-equilibrium, meta-population dynamics since ancient times.
Highlights
The central-marginal hypothesis postulates that genetic diversity of a species is likely to be lower, and genetic differentiation between its populations higher, at the limits of its range (WANG et al 2002; SCHWARTZ et al 2003)
Microsatellite markers were used to characterize the structure of genetic diversity in natural Moroccan Aleppo pine (Pinus halepensis Mill.) populations, the most southwesterly marginal populations of the species in the Mediterranean Basin
Successive founder events, repeated local extinctions, small effective population size and reductions in gene flow between populations are among the factors that can lead to a reduction in genetic diversity in marginal populations
Summary
The central-marginal hypothesis postulates that genetic diversity of a species is likely to be lower, and genetic differentiation between its populations higher, at the limits of its range (WANG et al 2002; SCHWARTZ et al 2003). Successive founder events, repeated local extinctions, small effective population size and reductions in gene flow between populations are among the factors that can lead to a reduction in genetic diversity in marginal populations These processes have often been overlooked in out-crossing, wind-pollinated tree species because analyses of neutral markers have generally revealed weak genetic partitioning among their populations (AUSTERLITZ et al 2000). Microsatellite markers were used to characterize the structure of genetic diversity in natural Moroccan populations of Pinus halepensis, which grow in the most adverse ecological conditions for the species in the Mediterranean basin. We hypothesized that successive population contractions (due to natural or human-induced disturbances) followed by expansions (due to the good potential for pines to regenerate) could be expected to be reflected in the genetic and demographic structure of the Aleppo pine populations.
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