Hybridisation processes in sympatric populations of pines Pinus sylvestris L., P. mugo Turra and P. uliginosa Neumann

Natural hybridisation was postulated between the closely related pine species Pinus sylvestris and the P. mugo complex, however no clear evidence on propagation of mature hybrids in nature has been documented so far. To test the hybridisation hypothesis we applied chloroplast DNA (cpDNA) markers and isozymes in the analyses of 300 individuals representing the variety of morphological forms in the sympatric populations of P. sylvestris, P. mugo and P. uliginosa at the peat bog complex in the Sudety Mts., Poland. Additionally, the haplotypes of paternally inherited cpDNA of 149 open pollinated progeny derived from seeds were compared to the haplotypes of parental trees to access the intensity and direction of contemporary hybridisation. The morphologically highly variable polycormic (multi-stemmed) hybrids between P. mugo and P. uliginosa were identified. The second group of hybrids was found among the monocormic (single-stemmed) P. sylvestris-like individuals carrying the cpDNA from P. mugo complex. Hybrids of P. sylvestris as a pollen donor and P. mugo or P. uliginosa as a mother were not found, either in the group of examined trees, or among the open pollinated progeny. The results indicate that numerous hybrids can exist in the sympatric population of the species studied and that gene flow can successfully proceed from P. mugo complex to P. sylvestris. Hybridisation and ecological selection seems to play a significant role in diversification and evolution of the investigated species.