Colonization of the Tibetan Plateau by the homoploid hybrid pine Pinus densata

Abstract

Pinus densata is an intriguingly successful homoploid hybrid species that occupies vast areas of the southeastern Tibetan Plateau in which neither of its parental species are present, but the colonization processes involved are poorly understood. To shed light on how this species colonized and became established on the plateau, we surveyed paternally inherited chloroplast (cp) and maternally inherited mitochondrial (mt) DNA variation within and among 54 populations of P. densata and its putative parental species throughout their respective ranges. Strong spatial genetic structure of both cp and mtDNA were detected in P. densata populations. Mitotypes specific to P. densata were likely generated by complex recombination events. A putative ancestral hybrid zone in the northeastern periphery of P. densata was identified, and we propose that the species then colonized the plateau by migrating westwards. Along the colonization route, consecutive bottlenecks and surfing of rare alleles caused a significant reduction in genetic diversity and strong population differentiation. The direction and intensity of introgression from parental species varied among geographic regions. In western parts of its range, the species seems to have been isolated from seed and pollen flow from its parent species for a long time. The observed spatial distribution of genetic diversity in P. densata also appears to reflect the persistence of this species on the plateau during the last glaciation. Our results indicate that both ancient and contemporary population dynamics have contributed to the spatial distribution of genetic diversity in P. densata, which accordingly reflects its evolutionary history.

Genetic structure of Pinus henryi and Pinus tabuliformis: Natural landscapes as significant barriers to gene flow among populations

“…mainly located in the Wuling and Bashan mountains, near a typical subtropical region with evergreen trees. Recently empirical studies of pines using by the niche modeling method indicated that strong ecological selection caused by distinct environmental factors, together with geographic isolation, played a critical role in speciation and population divergence of pines (Mao and Wang, 2011;Wang et al, 2011bWang et al, , 2011cZhao et al, 2014). Genetic boundaries coordinated with mountain systems have also been documented among populations by using Barrier software, (Line 1e3 in Fig.…”

Variations in electrical impedance and phase angle among seedlings of Pinus densata and parental species in Pinus tabuliformis habitat environment

“…densata originated from the natural hybridization in the northeast Tibetan Plateau and formed the pure forest in Linzhi valley for mostly four million years (Liu et al 2011;Fig. 2 Electrical impedance (EI) and phase angle (PHI) comparison for Pinus densata, Pinus tabuliformis, Pinus yunnanensis Variations in electrical impedance and phase angle among seedlings of Pinus densata and… 781 Wang et al 2011). Here, impedance parameters in P. densata in Maerkang were slightly higher than that in Linzhi, meaning that there are some needle tissue and cell structural differences between them.…”

Hybrid swarms: catalysts for multiple evolutionary events inSenecioin the British Isles

“…More recently, the role of newly introduced species as stimulants of hybridisation has been recognised (Seehausen 2004;Vellend et al 2007) because hybridisation is common when populations invade new environments and potentially elevates rates of response to selection, and predisposes colonising populations to rapid adaptive diversification under disruptive or divergent selection. The generation of new recombinant types within hybrid swarms is suspected to have facilitated the evolution of new homoploid hybrid species, for example, in Helianthus (Rieseberg et al 2003), Iris (Arnold et al 2012), Pinus (Wang et al 2011) and Senecio Brennan et al 2012). In the case of new allopolyploid taxa, molecular markers have demonstrated several independent origins at different locations (i.e.…”