The influence of a relict distribution on genetic structure and variation in the Mediterranean tree,Platanus orientalis

Abstract

The distribution of plant species around the Mediterranean basin is a product of the influence of both geographical barriers and of climatic changes experienced during the Tertiary, with the transition from a warm to cool periods. Several species, once largely distributed across the Northern Hemisphere, retracted to refugial areas in southern Europe where they are described as Tertiary relicts. Platanus orientalis is a typical representative of Tertiary flora in southwest Eurasia; its distribution spreads from the Caucasus to the Mediterranean, with its western border in Southern Italy and Sicily. We analysed genetic diversity and differentiation in the centre and western part of its distribution range using nuclear microsatellites and compared genetic parameters between core and western populations. We found an overall decrease in genetic diversity estimates (heterozygosity, private allelic richness) from central towards western populations, with those from Southern Italy and Sicily showing the lowest values. The low level of genetic diversity probably results from historic range fragmentation experienced by P. orientalis in its westernmost distribution as confirmed by high level genetic isolation of these populations. Ornamental hybrids were genetically distinguished from P. orientalis as contained private alleles, indicating that gene flow with natural populations is rare. Population assignment and neighbour-joining (NJ) analysis of populations identified four groups belonging to two main phyletic groups (the Southern Italian-Sicilian-Balkan and Cretan-Bulgarian-Turkish lineages) that seem to have different biogeographic origin and also excluded an artificial origin for southern Italian and Sicilian populations as previously suggested. These results show that quantifying the genetic variation of a Tertiary relict in a geographical context, and the potential effect of hybridization with introduced ornamental hybrids, can provide useful insights on factors influencing population genetic structure. Such information is crucial to predict how such taxa will respond to increasing anthropogenic influence on the environment.

A strong east–west Mediterranean divergence supports a new phylogeographic history of the carob tree (Ceratonia siliqua, Leguminosae) and multiple domestications from native populations

“…D.A. Webb ( N A = 17, Delplancke et al, ), or Phoenix dactylifera L. ( N A = 13, Zehdi‐Azouzi et al, ); but higher than in the Tertiary relict Platanus orientalis L. ( N A = 1.9, Rinaldi et al, ). La Malfa et al () reported a very similar N A value of 3.1 for nine SSR markers screened in carob cultivars from Italy, Malta and Spain.…”

Preliminary characterization of the Quercus pubescens complex in southern Italy using molecular markers

“…In many cases it was considered as acceptable to take a minimum of 10 to 30 individuals. For some Pinus sylvestris L. populations in the Baltic area, the number of 20-25 individuals was found to be large enough to detect all the alleles (Danusevičius et al 2016) whereas other studies have even considered significantly lower numbers (Kitamura et al 2017, Rinaldi et al 2019. In contrast, in Kalinowski (2005) it was shown particularly clearly that when F ST is less than 0.01 it can be useful to sample up to 100 individuals.…”

Population Genetic Diversity and Structure of Threatened Magnolia Species in Western Mexico

“…Thereby, we suggest that climatic changes in the recent past impacted forest distribution, leading to fragmentation of the forest in which Mexican Magnolia presently occur [23], and thus explaining the geographic distribution of the genetic variation. The in uence of the past glacial cycles was also observed in the Japanese Magnolia kobus [59] and the relict species Platanus orientalis, whose distribution is strongly in uenced by humidity and water availability, similar to magnolias [60].…”