Empirical assessment of the reproductive fitness components of the hybrid pine Pinus densata on the Tibetan Plateau

Abstract

Pinus densata is distributed on the Tibetan Plateau, where it forms extensive forests at high elevations. Genetic studies have provided evidence that P. densata originated through hybridization between P. yunnanensis and P. tabuliformis. To clarify the relationships among these pines, and assess their reproductive fitness in their respective habitats, we conducted a comparative analysis of eight cone and seed morphometric traits and six reproductive traits in them. Among the eight morphometric traits examined, six appeared to be intermediate in P. densata between those of P. yunnanensis and P. tabuliformis. There were significant differences among the three pines in all of the morphometric traits, and P. densata showed greater variability in these traits than the other two pines. In contrast to the morphometric traits, the reproductive traits (including the proportions of filled and empty seeds, ovule abortion rate, seed efficiency, meiotic abnormalities during microsporogenesis and pollen viability) differed little among the three pines, indicating that they have similar overall rates of effective pollination and fertilization in their respective natural environments. Despite their location on the high plateau, natural populations of P. densata appeared to have normal levels of reproductive success, comparable to those of the two parental species in their natural habitats. This study provides empirical data characterizing the reproductive success and adaptation of a Electronic supplementary material The online version of this article (stabilized homoploid hybrid in a novel habitat that is ecologically and spatially inaccessible to its parental species.

The role of seed traits as segregation factors of hybrids in wild populations ofCistus(Cistaceae)

“…Another example of fertile homoploid hybrids with enhanced or compensated fitness compared to the parentals has been reported in Pinus. Mao and Wang (2009) observed lesser seed mass and similar reproductive success in the stabilized homoploid hybrid Pinus from the sowing experiment were found (Table III). The seedling height and diameter, the stem diameter and the number of leaves in seedlings from hybrid seeds did not allow to detect any sign of anomalous growth, malformation or seedling decay.…”

“…Under such conditions only the formation of a sterility barrier can lead to certain reproductive isolation from the parental species (Grant 1981). Even after reproductive isolation, a hybrid or introgressive population will only survive thanks to some adaptive advantage for living in sympatry with the parents (Grant 1981;Burgess et al 2008) or by displaying some ecological divergence that permits colonization of an unoccupied habitat (Anderson 1949; Barton & Hewitt 1985;Buerkle & Rieseberg 2008;Mao & Wang 2009). Under these circumstances, we might say that a hybrid population has stabilized (Rieseberg 1997).…”

Impact of Geography and Climate on the Genetic Differentiation of the Subtropical Pine Pinus yunnanensis

“…Climatic conditions vary between regions divided by the mountain chains, and pronounced morphological variations in this pine have been recorded across its range [33], [34], [35], [36]. It has hybridized with another Asian pine, Pinus tabuliformis , generating a homoploid hybrid, Pinus densata [37], [38], [39], [40].…”

Genetic Variation Related to High Elevation Adaptation Revealed by Common Garden Experiments in Pinus yunnanensis

“…(Wu, 1956;Mao and Wang, 2011). P. yunnanensis morphological variation is significant across its range, and regions divided by mountain chains featuring different climatic conditions (Yu et al, 1998;Yu et al, 2000;Mao et al, 2009). Recent analysis based on maternally inherited mitochondrial (mt) and paternally inherited chloroplast (cp) DNA markers found continuous genetic differentiation over the majority of its range, and discrete isolated local clusters in the northwest and east peripheries.…”