Phylogeny of beech in western Eurasia as inferred by approximate Bayesian computation

Abstract

The <em>Fagus sylvatica</em> L. species complex in Europe and Western Asia comprises two commonly recognized subspecies, <em>F. sylvatica</em> subsp. <em>sylvatica</em> [= <em>F. sylvatica</em> sensu stricto (s. str.)] and <em>F. sylvatica</em> subsp. <em>orientalis</em> (= <em>F. orientalis</em>), and two putatively hybridogenous or intermediate taxa, “<em>F. moesiaca</em>” and “<em>F. taurica</em>”. The present study aimed to examine the demographic history of this species complex using 12 allelic loci of nine allozymes scored in 279 beech populations in western Eurasia. Three sets of phylogenetic scenarios were tested by approximate Bayesian computation: one dealing with the divergence of subspecies and/or regional populations within the whole taxonomical complex, and two others focusing on the potential hybrid origin of “<em>F. moesiaca</em>” and “<em>F. taurica</em>”. The best-supported scenario within the first set placed the time of divergence of regional populations of <em>F. orientalis</em> in the Early Pleistocene (1.18–1.87 My BP). According to this scenario, the Iranian population was the ancestral lineage, whereas <em>F. sylvatica</em> s. str. was the lineage that diverged most recently. “<em>Fagus taurica</em>” was found to have originated from hybridization between the Caucasian population of <em>F. orientalis</em> and <em>F. sylvatica</em> s. str. at 144 ky BP. In contrast, there was no evidence of a hybrid origin of “<em>F. moesiaca</em>”. The best-supported scenario suggested that the Balkan lineage is a part of <em>F. sylvatica</em> s. str., which diverged early from <em>F. orientalis</em> in Asia Minor (817 ky BP), while both the Italian and Central-European lineages diverged from the Balkan one later, at the beginning of the last (Weichselian) glacial period.