Phylogeography and conservation genetics of the lesser white-fronted goose (Anser erythropus)

Minna Ruokonen

Abstract

Analyses of mitochondrial control region sequences were used to infer phylogeny of Anser species, phylogeography of the lesser white-fronted goose, and genetic background of a captive stock.

The genetic distances among the Anser species ranged from 0.9 to 5.5% in the complete control region sequences and supported the view of close relatedness of these species. Among the four most closely related species, the bean, pink-footed, white-fronted and lesser white-fronted goose, the branching order is uncertain. The short internal branches and low support for the branching order suggest that the species have diverged recently within short time-intervals. The mtDNA tree obtained is incongruent with the traditional view of the species relationships, but the reasons for this remain to be clarified.

Two diverged mitochondrial lineages were found in the lesser white-fronted goose and a vicariant origin was proposed. Basal haplotypes are geographically widespread and indicate a recent common ancestry for populations. The derived haplotypes are confined to singular breeding populations and suggest restrictions to the present female gene flow. A shift in the frequency of the mtDNA lineages approximately coincides with a migratory divide in the Taimyr Peninsula. Low mtDNA diversity and significant difference in the haplotype frequencies observed in Fennoscandian subpopulation suggested that it should be considered as a management unit. The fossil record was examined to gain additional information about the colonisation history of the species, but was found to be of limited use.The captive lesser white-fronted goose stock used for reintroduction/restocking was shown to be incompatible with the Fennoscandian wild population. Some captive individuals carried the mtDNA of the white-fronted goose suggesting a hybrid origin. Hybridisation has probably occurred during captive propagation, but to clarify further the extent of introgression, nuclear markers should be applied.The structure and evolution of the control region were studied by comparing complete avian sequences. Saturation was found to occur at pairwise divergences of 10% as shown for third codon positions of the mitochondrial genes previously. In pairwise comparisons of the control region and cytochrome β sequences, the rate of divergence varied among the lineages. Two conserved sequence blocks showed considerable sequence conservation when compared to mammalian sequences.

Table of Contents

Acknowledgements

Abbreviations

List of original papers

1. Introduction

1.1. Phylogeny and phylogeography

1.2. Conservation biology and genetics

1.3. Mitochondrial DNA: the tool

1.3.1. Mitochondrial DNA
1.3.2. Mitochondrial control region

1.4. The geese

1.4.1. Life-histories and genetic consequences
1.4.2. Geese and conservation cases
1.4.3. The lesser white-fronted goose

2. Outlines of the study

3. Materials and methods

3.1. The species and populations
3.2. Molecular methods
3.3. Numts, nuclear copies of mitochondrial sequences
3.4. Sequence analysis

4. Results and discussion

4.1. Evolution of the avian mitochondrial control region
4.2. MtDNA phylogeny of the Anser geese
4.3. Ice ages and Anser fossil data
4.4. Intraspecific diversity of the lesser white-fronted goose
4.5. Genetic background of captive lesser white-fronted goose stock

5. Concluding remarks

List of Figures
1. General structure of the vertebrate mitochondrial control region. The arrows indicate the location of the H-strand replication origin and the bidirectional promoter for L- and H-strand transcription. TAS, termination associated sequence; F through B, conserved sequence boxes in the central domain; CSBs, conserved sequence blocks.
2. The effect of some life-history characteristics to the genetic structuring of the goose populations in maternally inherited mitochondrial DNA and W chromosome, and in biparentally inherited nuclear autosomal genes. In all the cases, the assumption is that the females show natal philopatry and the males wintering philopatry. In c) the degree of differentiation in nuclear genes depends on the degree of male natal philopatry. If assortative mating is involved, genetic structuring in both maternally and biparentally inherited markers may take place in a) trough c). Circle, a female; square, a male; solid line, female movements; dotted line, male movements.
3. Breeding distributions of a) the lesser white-fronted goose (circles), the white-fronted goose (alb = Anser albifrons albifrons, fro = A. albifrons frontalis), b) the pink-footed goose (bra = Anser brachyrhynchus), the bean goose (fab = A. fabalis fabalis, mid = A. fabalis middendorffii, ros = A. fabalis serrirostris, mid = A. fabalis middendorffii). The connections of the known lesser white-fronted goose breeding areas to the wintering areas in Greece and China and to a staging area in Kazakhstan are indicated by arrows.
4. Levels of mtDNA divergence among the complete avian control region sequences. The mean distance value and the range in pairwise comparisons within the genera are indicated. The number of species is shown in parenthesis, for a list of the species see Table 1 in I.
5. Localities for fossils of four Anser goose species during a) the Holocene, b) Isotope stage 2, and c) Isotope stage 3. In d) climatic fluctuations during the last 60 000 years are shown for northern France (left), Holland-northern Germany (centre) and Fennoscandia (right) (modified from Andersen & Borns 1997). Black, warm or relatively warm climate; grey, cold or relatively cold climate.
6. Comparison of mtDNA divergences within the goose species. The trees are constructed with the neighbor-joining method using the most variable part of the control region (Canada goose 143 bp, accession numbers AF175474-AF175497, Scribner et al., unpublished; snow goose 178bp, Quinn 1992; white-fronted goose 221 bp, IV; lesser white-fronted goose 221 bp, III).

		Next
		Acknowledgements

Homepage of this publication

Library Units | Collections | Databases | Library News | Library Services | Electronic Collection | Links elsewhere | Alphabetical Index

© 2000 Oulu University Library