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* Premise of the study: Geographically peripheral (marginal) populations are expected to have lower genetic diversity and higher genetic differentiation than geographically core (central) populations as a result of supposedly lower effective population size (No) and higher genetic drift, founder effect, fragmentation, and isolation in peripheral than in core populations. Here we ad- dress this issue for a long-lived plant species, eastern white cedar (Thuja occidenmlis). * Methods: Genetic diversity and population structure of 13 natural populations of eastern white cedar from its Canadian eastern peripheral and core natural ranges in New Brunswick, Nova Scotia, and Prince Edward Island were studied using six nuclear microsatellite DNA markers. * Key results: The core populations of eastern white cedar had significantly higher allelic diversity (mean A = 8.83, Ar = 8.13, Ae = 4.03) and Ne (428) than the peripheral populations (A = 6.64, Ar 6.15, Ae = 3.12, Ne = 198). However, expected heterozygosity was similar in the core (He = 0.64) and peripheral (He = 0.60) populations. Genetic differentiation was significantly higher among the peripheral (FST = 0.089) than among the core (FST 0.032) populations. No genetic differentiation (FST/Φ RT = 0.000) was detected between core and peripheral regions. * Conclusions: Peripheral populations have significantly lower N~ and genetic diversity in terms of allelic diversity (richness) and significantly higher genetic differentiation than the core populations of eastern white cedar in its Canadian eastern range. However, core and peripheral populations have similar levels of expected heterozygosity. Implications for conservation of eastern white cedar genetic resources are discussed. [ABSTRACT FROM AUTHOR]

Northwest Africa is a major hotspot of plant biodiversity, but very little is known about the Quaternary range dynamics of plant species in this region. Here we investigate the range-wide population structure and phylogeography of Atlas cedar (Cedrus atlantica), an emblematic forest tree endemic to Morocco and Algeria. We genotyped 261 individuals from 11 populations using AFLP markers. Data were analyzed using both conventional F[subST]-based techniques and Bayesian clustering. Overall population differentiation was high (F[subST] = 0.25). Two major groups of populations were identified, one distributed through the Rif and Middle Atlas mountains in Morocco and the other through the Algerian Tell Atlas and Aurës mountains as well as the Middle Atlas. Combined molecular and fossil data indicate that C. atlantica survived the Last Glacial Maximum in at least three disjunct refugia along the coast of the Mediterranean Sea, whereas the Middle Atlas, today the core of the species range, has been colonized relatively recently (<10000 yr BP). The colonization history of individual populations has left clear imprints in their present-day diversity, which may vary greatly even between nearby stands. Our study illustrates how integrating different data sources and analytical approaches can help elucidate complex range dynamics that would otherwise remain undeciphered. [ABSTRACT FROM AUTHOR]

Atlas cedar (Cedrus atlantica) is an ecologically and economically important forest tree species of northern Africa and is considered one of the endangered conifer species in the region. Chloroplast microsatellites (cpSSR) were used to study genetic variation within and among populations and geographical structure in natural populations of C. atlantica throughout its entire distribution range in Morocco. A total of 25 chloroplast haplotypes and 66 cpSSR alleles were found among 162 individuals. The cpSSRs indicate that C. atlantica appears to maintain a high level of genetic diversity (mean He = 0.95), as observed in most coniferous species. Values of mean pairwise distance within a population (D²SH) were related to the size and location of the populations. AMOVA analysis showed that most of the variation in C. atlantica occurs within populations and confirmed the general tendency of gymnosperms to display lower values of population differentiation than angiosperms. The distance-based clustering method (PCoA and neighbor-joining analysis) and the geographical structure revealed a poor structure among the six populations of Cedrus atlantica. Also, a Mantel test indicated a weak correlation between geographic and genetic distances (P = 0.106, r = 0.363). These results are also interpreted in the context of postglacial history of the region plus human impacts. [ABSTRACT FROM AUTHOR]

Cedrus atlantica (Pinaceae) is a large and exceptionally long-lived conifer native to the Rif and Atlas Mountains of North Africa. To assess levels and patterns of genetic diversity of this species, samples were obtained throughout the natural range in Morocco and from a forest plantation in Arbùcies, Girona (Spain) and analyzed using RAPD markers. Within-population genetic diversity was high and comparable to that revealed by isozymes. Managed populations harbored levels of genetic variation similar to those found in their natural counterparts. Genotypic analyses of molecular variance (AMOVA) found that most variation was within populations, but significant differentiation was also found between populations, particularly in Morocco. Bayesian estimates of FST corroborated the AMOVA partitioning and provided evidence for population differentiation in C. atlantica. Both distance- and Bayesian-based clustering methods revealed that Moroccan populations comprise two genetically distinct groups. Within each group, estimates of population differentiation were close to those previously reported in other gymnosperms. These results are interpreted in the context of the postglacial history of the species and human impact. The high degree of among-group differentiation recorded here highlights the need for additional conservation measures for some Moroccan populations of C. atlantica. [ABSTRACT FROM AUTHOR]