Asymmetric introgression between Pinus sibirica and Pinus pumila in the Aldan plateau (Eastern Siberia)

Pinus sibirica and P. pumila are Asian five-needle pines with vast geographic distributions that are partially overlapping. Natural hybrids with intermediate morphology have been found previously, but there is a lack of evidence of ongoing introgression. The goal of our study was to elucidate the genetic structure of P. sibirica and P. pumila populations growing in the north-east of their sympatry zone (Aldan plateau) using cytoplasmic DNA markers. All studied P. sibirica and P. pumila trees had usual species-specific growth habits. Using nad1 intron2 of mitochondrial DNA (mtDNA) and trnV of chloroplast DNA (cpDNA) we found that trees morphologically identified as P. sibirica had pumila-specific mtDNA. Moreover, some of them also had pumila-specific cpDNA. P. pumila trees were typical and had pumila-type cytoplasmic DNA markers. These results suggest that interspecific hybridization took place long ago and lead to introgression and cryptic hybrids with P. sibirica appearance and P. pumila mtDNA.