Abstract
The evergreen Quercus alnifolia and Q. coccifera form the only interfertile pair of oak species growing in Cyprus. Hybridization between the two species has already been observed and studied morphologically. However, little evidence exists about the extent of genetic introgression. In the present study, we aimed to study the effects of introgressive hybridization mutually on both chloroplast and nuclear genomes. We sampled both pure and mixed populations of Q. alnifolia and Q. coccifera from several locations across their distribution area in Cyprus. We analyzed the genetic variation within and between species by conducting analysis of molecular variance (AMOVA) based on nuclear microsatellites. Population genetic structure and levels of admixture were studied by means of a Bayesian analysis (STRUCTURE simulation analysis). Chloroplast DNA microsatellites were used for a spatial analysis of genetic barriers. The main part of the nuclear genetic variation was explained by partition into species groups. High interspecific differentiation and low admixture of nuclear genomes, both in pure and mixed populations, support limited genetic introgression between Q. alnifolia and Q. coccifera in Cyprus. On the contrary, chloroplast DNA haplotypes were shared between the species and were locally structured suggesting cytoplasmic introgression. Occasional hybridization events followed by backcrossings with both parental species might lead to this pattern of genetic differentiation.






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Acknowledgments
We would like to thank Andreas Christou, Constantinos Kounnamas, Salih Gücel, Zacharias Triftarides, Savvas Protopapas, Petros Anastasiou and the Department of Forests, Republic of Cyprus personnel, for their assistance during plant collections. We are grateful to Dr. Unai López de Heredia for stimulating discussions. This research was conducted in partial fulfillment for the doctorate degree of the first author at Albert-Ludwigs University of Freiburg. During that time, the first author was supported by doctorate scholarships from DAAD and the State of Baden-Württemberg. Partial financial assistance to Filippos Aravanopoulos in the form of two cooperative grants of the Ministry of Natural Resources of Cyprus and the Aristotle University of Thessaloniki is gratefully acknowledged.
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Communicated by K. Puettmann.
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Neophytou, C., Dounavi, A., Fink, S. et al. Interfertile oaks in an island environment: I. High nuclear genetic differentiation and high degree of chloroplast DNA sharing between Q. alnifolia and Q. coccifera in Cyprus. A multipopulation study. Eur J Forest Res 130, 543–555 (2011). https://doi.org/10.1007/s10342-010-0442-8
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DOI: https://doi.org/10.1007/s10342-010-0442-8