Detection of haplotypic variation and natural hybridization in halepensis-complex pine species using chloroplast simple sequence repeat (SSR) markers

In this investigation, nine chloroplast, paternally inherited simple-sequen ce repeat (cpSSR) markers were used to describe genetic variation of three closely related species belonging to the halepensis complex (Pinus halepens is Ait., P. brutia Mill. and P. eldarica Medwed.). Both the infinite allele model (IAM) and stepwise-mutation model (SMM) have been applied to the ana lysis of the genetic structure of natural populations and the geographical distribution of haplotypic variation. SMM-based estimators performed better than IAM-based estimators for large values of within-population diversity and divergence between population pairs. Overall, large haplotypic variatio n and high genetic divergence were detected for both P. halepensis and P. b rutia. The genetic structures of the three species are discussed with consi deration to the evolutionary and ecological characteristics of these specie s. Three highly informative markers showing size variants distinguishing P. halepensis from the other two species were used to provide more informatio n on the occurrence of natural hybridization in a Turkish sympatric populat ion of P. halepensis and P. brutia. Strong evidence of introgression of 'ha lepensis' chloroplast haplotypes into P. brutia seeds (but not vice versa) was detected. According to previous evidence from controlled crossings, mat ings between the above species seem to be successful only when P. halepensi s is the pollen donor and P. brutia is the female parent (but not reciproca lly). The existence of unidirectional gene flow in sympatric: populations c onfirms previous evidence about partial reproductive barriers between P. ha lepensis and P. brutia. Implications of the above evidence for the evolutio nary history of these species are discussed.