Phylogeography and allopolyploidization of Magnolia sect. Gynopodium (Magnoliaceae) in subtropical China

Abstract

Magnolia sect. Gynopodium is an evergreen tree aggregate which includes five species exhibiting three different ploidy levels: diploid, tetraploid and hexaploid. These species have a broad distribution throughout subtropical China and extend to adjacent regions of Indochina. The chloroplast psbA-trnH sequences were used to examine the genetic structure and phylogeographical patterns for elucidating the glacial refugia and migration history of species within section Gynopodium, and the single-copy nuclear gene LEAFY sequences were cloned to retrieve the different distinct allelic sequences for inferring the polyploid origins. Seven chloroplast distinct haplotypes were identified for all the individuals within section Gynopodium. The ancestral haplotypes were confined to the eastern edge of Yun-Gui Plateau, Emei Mountain and the northwest Yunnan. All examined nuclear LEAFY allelic sequences were clustered into three distinct clades. Those of two diploid species were recovered as monophyletic and nested within the same clade, whereas those of the tetraploid and hexaploid species were placed into two and three different clades, respectively. The clear-cut geographical distributions of ancestral chloroplast haplotypes indicated multiple potential refugia for species within the section Gynopodium; the chloroplast haplotype distribution patterns suggested that these species experienced different migratory histories. The nuclear LEAFY phylogenetic pattern, combined with evidence from chloroplast data, showed that both allopatric differentiation and allopolyploid origin involving hybridization likely took part in the rapid evolution of the section Gynopodium.