High genetic diversity within but limited differentiation among populations of the vulnerable Guatemalan fir

Genetic diversity in fragmented tree populations may reflect provenance variation and the relationship between genetic diversity and population characteristics should be known to improve conservation strategies. We chose the vulnerable Abies religiosa subsp. mexicana (syn. Abies guatemalensis) to study genetic diversity within and among 18 populations in Guatemala (284 trees, seven microsatellite markers). Genetic diversity was high in all populations (observed heterozygosity = 0.70-0.90), while six populations deviated from Hardy-Weinberg equilibrium. Inbreeding within populations (F_is) was significant in five populations, among them two peripheral populations. A cluster analysis and a principal component analysis (PCA) indicated existence of one large metapopulation with the two peripheral populations as outliers. Longitude, geographic isolation and expected heterozygosity were correlated with the first PCA axis, while altitude was correlated with the second axis. Mountain range, forest size and fitness traits of the provenances were not correlated with genetic diversity. The study indicated that peripheral populations of A. religiosa subsp. mexicana contained unique genetic information which should be included in ex situ conservation programmes, whereas the other populations in Guatemala showed little evidence for inbreeding or genetic erosion. We conclude that fragmented conifer populations can maintain high genetic diversity, while differentiation among populations can be weak.