Detection of ephemeral genetic sub-structure in the narrowendemic Abies nebrodensis (Lojac.) Mattei (Pinaceae) using RAPD markers

A. nebrodensis (Nebrodi fir, Sicilian fir) is restricted to a small area of the Madonie Natural Park in Sicily. According to recent estimates, its only population consists of 30 adult individuals and a fluctuating number of juveniles derived from natural regeneration; besides, some hundreds of cultivated plants are preserved as ex situ collection. We used RAPD data from six 10-mer primers to examine the consequences of extensive historical clearance and human pressures on the extant population. Data from multiple life stages and different habitat conditions were considered, affording an opportunity to ascertain for the first time the structure of genetic variation in the extant uneven-aged population on both spatial and temporal scale. Consistent with previous works, we found that the history of disturbance and past land use did not affect drastically the biological diversity of the present-day population. Considerable levels of genetic variation were detected both in adult and juvenile sets. The non-significant correlation between genetic and physical distances (Mantel test; r = - 0.075) revealed a random distribution of genotypes in the natural stand. When the juvenile set was divided in 17 subsets, based on maternal provenance and growing conditions, Shannon's index (54%) and AMOVA analysis (84%) indicated that most of genetic variation resides within subsets. Neighbour-joining cluster analysis supported the hypothesis of high crossfertilization rates expected for a woody perennial species; nevertheless some grouping of related individuals suggested partial inbreeding and a weak pattern of genetic structure. Changes in structure can occur as the progeny ages and offspring thinning is responsible for moulding patterns of genetic diversity and population structure in time.