Adaptive Variation In Seedling Traits Of Pinus Densata,Pinus Tabuliformis,Pinus Yunnanensis And Interspecific Hybrids In High Altitude Niche

Pinus densata is one of the most documented cases of homoploid hybrid speciation.This species originates from natural hybridization between Pinus tabuliformis and Pinus yunnanensis,and occupies a high altitude niche on the Tibetan Plateau.Based on natural distribution,the speciation of P.densata is considered a consequence of adaptive divergence to parental species.However,evidence from field experiments is still lack and required to provide information of fitness of P.densata with related pine complex.To clarify the mechanism of adaptive speciation,we conducted a series of field experiments in typical habitat of P.densata,with mati-populations of P.densata,P.tabuliformis,P.yunnanensis and interspecific hybrids.We assessed the fitness variation among these species/hybrids and checked the change of population genetic constructions coupling with ecological selection in high altitude.We expect to evaluate the fitness variation between P.densata and parental species,to assess the fitness of interspecific hybrid between P.tabuliformis and P.yunnanensis,to examine the roles of cytoplasmic inheritance in speciation of P.densata,and even to explore the habitat selection on population genetic of pine species.Based on seedling test of P.densata with parental species,we found significant variation of fitness-related traits between P.densata and parental species.The seedling survival rate and growth rate of P.densata in experimental conditions were higher than that of the parental species P.tabuliformis and P.yunnanensis,indicating a better fitness of P.densata in high altitude.A few of geographic populations of parent species show generally well fitness,but still lower than P.densata.January average temperature,precipitation and illumination factor may be limite the growth and survival of parents species on Tibetan Plateau.Artifical hybrids between P.tabuliformis and P.yunnanensis representative the initial hybrids which is the ancestor of P.densata.In this stdy,we found significant difference between reciprocal hybrids for seedling bud set rate and seedling high,which maybe indicative of a distinguished adaptation of initial hybridization on Tibetan Plateau.Additionally,reciprocal hybrid show similar survival rate in high altitude niche,suggesting that both reciprocal hybrid are likely to be the ancestor of population of P.densata.Surviving seedlings of P.tabuliformis×P.yunnanensis show obviously better fitness than parental species at the 4th year,which is an evidence that transgressive performance could be carry out by hybridization.Bud set rate of each species increase with the annual,which maybe indicative of the natural selection in high altitude niche.SSR markers are used to check the change of genetic structural parameters under habitat selection.The expect heterozygosity of interspecific hybrid was significantly decreased from 1 years seedling to 3 years seedling,suggesting strong habitat selection in test site.The diversity index of P.densata is smaller than that of the interspecific hybrid,reflecting the differences between the interspecific hybrid of P.tabuliformis×P.yunnanensis and the P.densata.The genetic distance between the interspecific hybrid and the P.densata is much smaller than with the parental suggestive the hereditary connection between the initial hybrids and the evolved species.P.densata is an important ecological tree in the eastern of Tibetan Plateau and represents a successfull case of homoploid hybrid speciation.This study assess the fitness variation among P.densata,P.tabuliformis,P.yunnanensis and the interspecific hybrid,reveal the ecological genetic foundational of speciation of P.densata,and discusses the environment association to fitness of pine complex.This study will increase our knowledge of the processes of speciation in P.densata by experimental evidences,and providing information for genetic breeding and conservation.