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In this study, we cloned and sequenced the complete mitochondrial DNAs of Chinese goose, Anser cygnoides populations from three different areas of Hunan province in China. The Anser cygnoides breed Wugangtong white goose (WGTW) sample and Wugangtong grey goose sample (WGTG) were taken from the Wugang county of Shaoyang city, the Anser cygnoides breed Xupu goose (XP) sample was taken from the Xupu county of Huaihua city, and the Anser cygnoides breed Yanling white goose (YLW) sample was taken from the Yanling county of Zhuzhou city. The organization of the four Anser cygnoides breeds mitochondrial genomes was similar. Phylogenetic analyses using N-J computational algorithms showed that the analyzed species are divided into four major clades: Anatinae, Anserinae, Dendrocygninae and Anseranatidae. It was noted that Wugangtong white goose, Yanling white goose and Xupu goose have highly similar phylogenetic relationship.

The bean goose Anser fabalis and the pink-footed goose A. brachyrhynchus breed in the tundra and taiga zones of Eurasia and eastern Greenland, and the taxonomy of the group based on morphology has been controversial. We investigated the phylogenetic relationships within the bean goose-the pink-footed goose complex using mitochondrial control region sequences of 199 individuals collected from the breeding areas in the Palaearctic and Eastern Nearctic. We found three mitochondrial clades geographically distributed to (1) Greenland, Iceland and Svalbard (A. brachyrhynchus), (2) the eastern taiga zone (former subspecies A. fabalis middendorffii), and (3) the western taiga and the tundra zone (subspecies A. fabalisrossicus, serrirostris and fabalis). MtDNA phylogeny suggests that morphological affinities between the taxa, e.g. in the bill structure, result from convergent evolution due to adaptation to similar habitats. Although a latitudinal cline in morphology was observed, clear phylogenetic discontinuities exist in the taiga and tundra zones supporting a species status for brachyrhynchus and middendorffii.

It has generally been assumed, based on morphology, that Chinese domestic goose breeds were derived from the swan goose (Anser cygnoides) and that European and American breeds were derived from the graylag goose (Anser anser). To test the validity of this assumption, we investigated the mtDNA cleavage patterns of 16 Chinese breeds and 2 European breeds as well as hybrids produced between a Chinese breed and a European breed. After 224 mtDNAs, isolated from the Chinese and European breeds, were digested by 19 restriction endonucleases, variations of the cleavage patterns were observed for four enzymes (EcoRV, HaeII, HincII, and KpnI). All Chinese breeds and their maternal hybrids except the Yili breed showed an identical haplotype, named haplotype I or the Chinese haplotype; the European breeds and the Yili breed showed another haplotype, named haplotype II or the western haplotype. None of the haplotype found in the Chinese type was detectable in the western type and vice versa. The two haplotypes were found to differ from each other at 8.0% of the sites surveyed and with a 0.72% sequence divergence. Using 2% substitution per million years calibrated from the genera Anser and Branta, the two domestic geese haplotypes were estimated to have diverged approximately 360,000 years ago, well outside the 3000-6000 years in domestic history. Our findings provide the first molecular genetic evidence to support the dual origin assumption of domestic geese in the world. Meanwhile, the four mtDNA restriction fragment length polymorphisms can be used as maternal genetic markers to distinguish the two types of domestic geese.

The 1 042 bp control region of mitochondrial DNA from 84 geese of 15 domestic goose breeds was sequenced and genetic differentiation was analysed. Results showed that the interpopulation nucleotide divergence was highest (3.805% -4.067%) between Yili and the other 14 breeds. The average nucleotide diversity variation within different domestic breeds was 0 - 0.116%. Excluding the Yili, the interpopulation nucleotide divergence between Huoyan and the remaining breeds, was 0.211% - 0.272%, which was significantly higher than that between any other two breeds (0 -0.094%). During the formation of domestic breeds in China,there is an association between the genetic differentiation of domestic geese and their geographic distribution. The divergence time of Huoyan breed was relatively earlier and genetic drift may have been the main factor to affect the genetic differentiation of the Huoyan breed (Nm = 0.02 -0.54). On the other hand, gene flow is the main reason for the lack of a clear differentiation among the remaining 13 Chinese domestic geese breeds (Nm = 12.0 - 65.33).

The mitochondrial cytochrome b (cyt b) gene of 17 breeds of domestic goose (2 in Europe and 15 in China) was sequenced and compared with that of the representative of wild species Anser albifrons. Sequence analysis revealed that thirty-one variable sites and 4 different haplotypes were found among the 45 sequences examined, and nucleotide diversity and haplotype diversity were 0.0068 and 0.45, respectively. Mutations of insertion/deletion were not found. Across all sites,the abundance of G was low (14.2%), whereas the percentages of A, T, and C were quite similar among three Anser goose species. The frequency of guanine differs greatly among the three codon positions. Compositional bias is smaller at first and second positions (0.057 and 0.223) than at third positions (0.492), the probability of transition was higher than that of tranversion (Ts/Tv=9.5-19), there was the highest number of transition in the third codon. The phylogenetic analysis support the hypothesis of dual origin of domestic geese.

Population structure and phylogeography of the pink-footed goose, Anser brachyrhynchus Baillon 1833, was studied using mtDNA control region sequences (221 bp) from 142 individuals. Present breeding areas of the species in Greenland, Iceland, and Svalbard were largely covered by ice during the late Pleistocene. In pairwise comparisons phiST estimates showed significant differentiation among eastern and western populations, whereas sampling localities within both areas were not differentiated. The mtDNA data indicate that the populations have separated recently (less than 10 000 years ago) and present breeding areas were colonized from one refugial population. The levels of haplotype and nucleotide diversity were approximately five times higher for the eastern population compared to the western population and suggest that the latter was colonized by a subset of eastern birds. Time to the most recent common ancestor of the species is 32 000-46 000 years, i.e. the present mtDNA variation of the pink-footed goose has accumulated during the last 0.1 My. Estimates of the long-term female effective population size (5400-7700 for the eastern population) imply that the refugial population of the pink-footed goose has been large. Tundra habitats were more extensive in cold periods of the late Pleistocene than today and may have sustained population sizes that allowed the accumulation of extant genetic polymorphism. It is not probable that the postulated small refugial areas in the high latitudes had a significant role in maintaining this diversity.

Phylogenetic analysis of 1.35 kb of mtDNA sequence from fossils revealed a previously unknown radiation of Hawaiian geese, of which only one representative remains alive (the endangered Hawaiian goose or nene, Branta sandvicensis). This radiation is nested phylogenetically within a living species, the Canada goose (Branta canadensis) and is related most closely to the large-bodied lineage within that species. The barnacle goose (Branta leucopsis) is also nested within the Canada goose species and is related most closely to the small-bodied lineage of Canada geese. The peripheral isolation of the barnacle goose in the Palearctic apparently allowed the evolution of its distinctive plumage pattern, whereas the two Nearctic lineages of Canada geese share a primitive plumage pattern. The Hawaiian lineage of Canada geese diverged more dramatically, splitting into at least three species that differ in body size, body proportions, and flight ability. One fossil species, limited to the island of Hawaii, was related closely to the nene but was over four times larger, flightless, heavy-bodied and had a much more robust cranium. Application of a rate calibration to levels of DNA divergence suggests that this species evolved on the island of Hawaii in less than 500,000 years. This date is consistent with the potassium/argon-based age of the island of Hawaii of 430,000-500,000 years. The giant Hawaii goose resembles the moa-nalos, a group of massive, extinct, flightless ducks that lived on older Hawaiian Islands and thus is an example of convergent evolution of similar morphologies in island ecosystems.

Mitochondrial DNAs (mtDNAs) of 138 samples from 11 domestic goose breeds in China were investigated by digesting, with 19 restriction endonucleases. Of 19 enzymes used, seven (Bcl I, Dra I, Eco RV, Hae II, Hinc II, Kpn I, Sac I) detected polymorphic patterns. By combining 27 restriction morphs, 138 individuals were classified into 6 mtDNA haplotypes. Phylogenetic tree was constructed by using UPGMA. There was no shared haplotype between Yili breed and the other 10 breeds. Genetic distance and UPGMA tree also suggested that Yili breed and other breeds came from different ancestors. Yili breed originated from Anser anser and other 10 breeds originated from Anser cygnoides. Restriction morphs digested with 4 enzymes (EcoRV, Hae II, Hinc II and Kpn I) could be used as maternal genetic markers to distinguish the two types of domestic geese. Mitochondrial DNA polymorphism was observed in the ten breeds of Anser cygnoides. Nucleotide diversity (pi), genetic distance between the two types and the average genetic distance among the ten breeds were estimated to be 0.025%, 0.266%, 0.029%, respectively. The breeds with white plume were affected by founder effect when they were formed. Swan domestic geese, Anser cygnoides domesticus, in China might come from two different populations of Anser cygnoides at two different places.