A Study On Mating System And Gene Flow Of Pteroceltis Tatarinowii, Endemic To China

Tertiary relict Pteroceltis tatarinowii Maxim.(Ulmaceae), one of the temperate canopy tree in the mainland of China, is the sole representative of the genus Pteroceltis. The species has been listed as a member of the national grade Ⅲ rare and endangered plants. P. tatarinowii is distributed widely across the temperate and subtropical regions exclusively in China. However, influenced by its biological characters and human impact, the extant populations of this species are scattered in isolated stands and the population quantity and size are in the declining trend. Current studies on this species mainly focus on the community structure analysis, cultivation of the economic forest and population genetic structure revelation, but the mating system of P. tatarinowii still remains unclear. The mating system of species is closely related to its evolution and directly affects the distribution, genetic structure and the population evolution of the species. It is also the important reference to artificial cultivation of the species. In this study, we discussed the mating system and gene flow of P. tatarinowii, revealed the dispersal distance and pattern of effective pollen and analyzed the factors that would affect the mating system and pollen flow based on parentage analysis using 12 SSR primers, aiming to provide information to shed light on genetic structure and breeding mechanism of P. tatarinowii and also provide scientific guidance for drawing up conservation strategies of this economic species. The main results were as follows:1. The Hardy-Weinberg test of 12 polymorphic loci showed that Loc11、Loc17 in Family QTS-1, Loc9 in Family QTS-2,Loc42 in Family QTS-10 respectively deviated from Hardy-Weinberg equilibrium. All the other loci conformed to the Hardy-Weinberg equilibrium. None of the 12 pairs of primers was found deviated from Hardy-Weinberg equilibrium in all families. Therefore, these 12 pairs of primer we screened were appropriate to the parentage analysis and mating system analysis.2. We chose ten wild families of P. tatarinowii to test the polymorphism of the loci. The results showed that 12 pairs of primers displayed high levels of polymorphism. The number of alleles per locus ranged from 5 to 17 with an average of 8.083 and a total of 97. The average expected heterozygosity was 0.677. The average observed heterozygosity was 0.656. The average PIC value was 0.633. The paternity analysis using Cervus software assigned the real paternity for its 104 progenies which accounted for 43.9 % of total offspring with 95% confidence level.3. The analysis for 237 open-pollination offspring by SSR markers showed that the average Shannon’s information index was 1.3735 and the average fixation index was 0.0537. The average genetic differentiation coefficient was 0.1710 which indicated that the majority of genetic variation occurred within families. AMOVA analysis results showed that in the whole population of P. tatarinowii, 91.15 %(P < 0.01) of genetic variation occurred within families. Thus, the genetic variation primarily existed within families, indicating frequent gene flow existed within families of P. tatarinowii.4. UPGMA phylogenetic tree and Gentix factor correlation analysis(FCA) showed a consistent relationship clustering among populations. 10 families were divided into five groups: Family QTS-1, Family QTS-2, Family QTS-4, Family QTS-3 and Family QTS-10, the remaining families were in one group. The grouping might be caused by certain differences in plant density, altitude, wind direction and anthropogenic disturbance within families, which could affect the mating patterns of P. tatarinowii.5. The mating system of P. tatarinowii was analyzed in this study. The average multi-locus outcrossing rate was 0.987±0.011. The average single-locus outcrossing rate was 0.959±0.096. The multi-locus outcrossing rate did not significantly differ from the single-locus outcrossing rate(tm-ts=0.028). The results indicated that outcrossing was predominant in the open-pollinated breeding population of P. tatarinowii and the priority is outbreeding with a considerable inbreeding existed.6. The average effective pollen dispersal distance of P. tatarinowii was 46.14±11.52 m. The result showed that the mating distance of each maternal tree appeared to present normal distribution respectively which made further efforts to reveal the outbreeding mode of P. tatarinowii.