Unexpected scenarios from Mediterranean refugial areas: disentangling complex demographic dynamics along the Apennine distribution of silver fir

Abstract

Mediterranean refugial areas are generally underrepresented in large-scale genetic surveys of forest trees. In the case of silver fir (Abies alba Mill.), this has led to divergent hypotheses about the exact location of glacial refugia and the trajectory of recolonization routes. Based on the comprehensive sampling of Apennine populations, we aimed to reconcile discrepancies about the number and location of refugia for silver fir in the Apennines and test alternative demographic scenarios developed from palaeobotanical and genetic data. Location Mediterranean Basin; the Apennines and surrounding areas.Methods 1167 individuals from 16 Apennine populations, extensively covering the species’ distribution along the Italian Peninsula, and eight populations from the Alps and Eastern Europe were genotyped at 16 nuclear and three chloroplast microsatellite markers. The geographical distribution of genetic variation was explored using Bayesian clustering and multivariate methods. Based on the inferred genetic structure, the demographic history of A. alba was assessed by the approximate Bayesian computation (ABC) analysis.Results Two unexpected characteristics of genetic structure emerged: a sharp genetic boundary in the central Apennines and a tight genetic connection between southern Apennine and Eastern European gene pools. Two Apennine areas, corresponding precisely with refugial areas hypothesized in most recent palaeobotanical syntheses, have high genetic diversity on a par with Eastern European populations. ABC analysis showed an ancient separation between Apennine and Eastern European gene pools followed by an admixture event that, mainly through directional gene flow via pollen, might have established the genetic similarity between southern Apennine and Eastern European populations. In addition, there was evidence that the central Apennines acted as a small-scale, isolated refugium during the Last Glacial Maximum. Main conclusionsSilver fir rear edge populations have experienced a complex demographic history across several glacial-interglacial cycles, leading to unexpected genetic structure. Our study provides new insights into forest tree dynamics in the Mediterranean, showing the putative presence of multiple refugia for silver fir in the Apennines and a trans-Adriatic connection between silver fir populations in the southern Italy and the Balkans

Studies on the Glacial Refugia of Forest Trees on Balkan Peninsula

“…Multiple refugia were found for the same species in other studies [35,36] and the contemporary map of genepool distribution is complicated additionally by the existence of suture zones and introgressive hybridization [37]. Existing of multiple refugia is not unprecedented in this species, as reported also for Iberian Peninsula [38].…”

Some refinements on species distribution models using tree-level National Forest Inventories for supporting forest management and marginal forest population detection

“…), whose Italian ranges are both characterised by the presence of widely disjoint meta-populations. Due to their valuable economic and ecological importance, both species are well studied at the European scale in terms of distribution of genetic diversity (Rose et al 2009, Piotti et al 2017, adaptive traits (Kerr et al 2015, Kramer et al 2017, and impacts of climate change on their spatial distribution (Schueler et al 2013, Tinner et al 2013). In addition, many marginal forest populations (MaPs) of both species do exist in Italy as possible target of FGR management.…”

“…Endangered gene pools may require transfer measures aimed at maintaining genetic diversity through assisted gene flow and assisted migration protocols based on robust data and models (Hamann et al 2015), as well as on the knowledge of adaptive traits and the spatial distribution of genetic diversity (Kramer et al 2017, Piotti et al 2017. Recently, forest research has focused on the impact of climate change on forest resources and their spatial distribu-tion (Isaac-Renton et al 2014, Marchi et al 2016, and on changes in the provision of ecosystem goods and services , Ray et al 2017, in order to support forest management strategies under climate change.…”

Exploring Nonlinear Intra-Annual Growth Dynamics in Fagus sylvatica L. Trees at the Italian ICP-Forests Level II Network

“…However, the low variance explained by GAMM was an expected result of this study. Indeed, while most of the variability on growth and stand structure is often driven by climate in non-disturbed stands [9,20,57,58] the same does not hold true for the ICP-Forests network. The analyzed dataset is composed by different forest categories including both coppices (TOS3, LIG1), grown-up high forests (ABR1, CAL1, CAM1, PIE1, PUG1, VEN1) with different structures and responses driven by age [32].…”