Research On Phylogeographic Structure And Hybridization Of Alectoris Partridge In China

Przevalski partridge (Alectoris magna) is endemic in China with limited range, and was identified as two subspecies, a nominate subspecies A. m. magna residing in the Chaidamu Basin and A. m. lanzhouensis residing around the Lanzhou Basin. Chukar partridge (Alectoris chukar), however has numerous subspecies with broad distribution. Both of them are indicative birds of arid and semiarid environments in northern China. The uplift of Tibetan Plateau is the important factor influencing climate severity and desert evolution in northwestern China, and it maybe affect historic evolution and phylogeographic structure of the two partridges severely accompanying with Pleistocene glaciation. At present, mtDNA marker was used for analyzing phylogeny and genetic structure of species. We used polymerase chain reaction (PCR) and direct sequencing methods to infer their genetic and phylogeographic structure based on mitochondrial cytochrome b (Cytb) and mtDNA control region (CR) data. The aims are: (1) to analyze Przevalski partridge in the Xining should belong to which subspecies; (2) to compare genetic variation within and among local populations between Przevalski partridge and Chukar Partridge; (3) to illuminate their phylogeographic relationship; (4) to infer their historic demography; (5) to speculate the time of hybridization happening, and confirm the geographic range of hybridization; (6) to compare the differences between two markers.We sampled 106 Przevalski partridges and 48 Chukar partridges for Cytb analyzing, also sampled 133 Przevalski partridges for CR analyzing.There were significant differences in nucleotide compositions between Cytb and CR gene, and the number of G + C was larger in the latter. The frequency of sequences variation of the latter was 9 times higher than the former.The Codon Bias Index (CBI) showed that Cytb gene had compositional bias within two partridges, and they had similar CBI. There were significant differences in total nucleotide compositions and no significant differences in 2^nd positions of codons between two partridges. The nucleotide compositions differed significantly among 13 local populations of Przevalski partridge, but no significant differences among 8 populations and subspecies of Chukar partridge (there were only significant differences in Cytosine, Adenine and Guanine of the 3^rd positions of condons among 8 populations).8 variable sites defined 9 haplotypes of Cytb gene in 98 Przevalski partridges. There was 0.97% sequences variation; 6 synonymous substitutions in 8 substitutions; the number of transitions between T and C was 1.5 times higher than that between A and G. 14 variable sites defined 12 haplotypes of Cytb gene in 133 Chukar partridges. There was 1.69% sequences variation; 11 synonymous substitutions in 15 substitutions; the number of transitions between T and C was less than that between A and G slightly, which was different from the nucleotide variation of CR gene in Chukar partridge in which there was higher pyridine variation (Huang et al., 2004). The mutation direction of Cytb gene in two partridges was mainly from G to A and from T to C.As viewed from genetic distances and phylogenetic tree, we could speculate that the Przevalski partridges in Xining pop-group should belong to the Lanzhou subspecies (A. magna lanzhouensis). There was partly genetic divergence between the Xining pop-group and the Lanzhou pop-group.According to nucleotide compositions and genetic diversity of Cytb sequences, Chukar partridges had less genetic divergence and more frequently gene flow than Przevalski partridge. There was no distinctly genetic divergence among local Chukar partridge populations.Calibrated rates of molecular evolution suggested that Przevalski partridge and Chukar partridge could have speciated about 1.90 million years ago, affected by the Pleistocene second frigid and the form of Chaidamu Basin. The divergence time was about 0.27 Myr between the Chaidamu pop-group and the other two pop-groups (xining pop-group and Lanzhou pop-group), and about 0.19 Myr between Xining pop-group and Lanzhou pop-group, we speculated that the dispersal route was that Alectoris magna dispersed from Chaidamu Basin east to Lanzhou Basin, at last formed a dispersal star-like mode surrounding Lanzhou Basin step by step, and the Xining pop-group was formed by the Lanzhou pop-group dispersing back to west.All of the Przevalski partridge populations accepted sudden expansion model. the Lanzhou pop-group expansion began at 0.107Myr, and the Xining pop-group expansion began at 0.117. among Chukar partridge populations, the SB, QF and HLS populations were possible to suffer bottleneck effect, and sudden population expansion later.Lack of shared haplotypes of CR suggested that the phylogeographic structure of Przevalski partridge belonged to "Phylogenetic distinuity, spatial separation" pattern. There was "Phylogenetic continuity, partial spatial separation" geographic pattern between Lanzhou pop-group and Xining pop-group. To deduce from divergence of Cytb gene, the phylogeographic structure of eight Chukar partridge populations belonged to "Phylogenetic distinuity, lack of spatial separation". There were both lack of shared hayplotyes of CR and Cytb between Przevalski partridge and Chukar partridges, which had a "Phylogenetic distinuity, spatial separation" geographic pattern.There were 8 Przevalski partridges from five populations having Chukar partridge Cytb genotype. However, there were no Chukar partridge with Przevalski partridge's genotype. Thus, we could make sure that the hybridization between two partridges was introgression hybridization, maybe as result of sexual selection. The introgression hybridization was about 130km wide and 400km long from the surrounding of the Liupan Mountains to Lixian County. The time of hybridization happening was about 90 thousand years, which showed that the hybridization happened after the Lanzhou Przevalski partridge pop-group expanded to encounter with Chukar partridge population (the expansion time of Przevalski partridge was 0.107Myr ago).Analysis of Cytb gene indicated that introgression hybridization had no significant influence on genetic diversity of Przevalski partridge population. The low genetic diversity of hybrids and single haplotypes might indicated that mating selection between Chukar partridge female and Przevalski partridge male was not stochastic. It is possible that those Chukar partridges with specific genotype could mate with przevalski partridges, as a result, the hybrid offspring had single genotype. However, it just is a speculation, looking forward to advanced studies.