PHYLOGEOGRAPHY OF THE MALLARD (ANAS PLATYRHYNCHOS): HYBRIDIZATION, DISPERSAL, AND LINEAGE SORTING CONTRIBUTE TO COMPLEX GEOGRAPHIC STRUCTURE

Auk, The, Jul 2005 by Kulikova, Irina V, Drovetski, Sergei V, Gibson, Daniel D, Harrigan, Ryan J, Et al

ABSTRACT.-

Population genetic variation in Mallards (Anas platyrhynchos; n = 152) from Western Russia, North Asia, the Aleutian Islands, and mainland Alaska was investigated using 667 base pairs of the 5'-end of the mitochondrial DNA (mtDNA) control region. DNA sequencing revealed two clades that correspond to Avise et al.'s (1990) group A and B mtDNA haplotypes. Group A haplotypes (80.3%) were wide-spread in all localities from Western Russia to Alaska. Group B haplotypes (19.7%), by contrast, were found primarily in mainland Alaska, where they occurred at high frequency (77.4%), but they also occurred at low frequencies (declining east to west) in the Aleutian Islands (11.8%) and the Primorye region of North Asia (4.4%). Group B haplotypes were not observed in Western Russia or elsewhere in North Asia outside Primorye. Consequently, Mallards exhibited substantial genetic structure between Old World and New World (Φ^sub ST^ = 0.4112-0.4956) but possessed little genetic structure within the Old World continental area (Φ^sub ST^ = 0.0018). Nonetheless, when only group A haplotypes were included in the analysis, Mallards from the Aleutian Islands differed (albeit with low levels of divergence) from each of the other three sampled regions in the Old World and New World (Φ^sub ST^ = 0.0728-0.1461, P

Keywords: Anas platyrhynchos, hybridization, incomplete lineage sorting, Mallard, paraphyly.

Key words: Anas platyrhynchos, hybridization, incomplete lineage sorting, Mallard, paraphyly.

PHYLOGEOGRAPHIC PATTERNS OF birds (Aves) have been studied at various geographic scales. However, relatively few Holarctic waterfowl (Anatidae) species have been studied (Cronin et al. 1996, Lanctot et al. 1999, Scribner et al. 2001, Kulikova et al. 2004, Pearce et al. 2004). Waterfowl are an important migratory component of the Holarctic avifauna, and their phylogeography and population genetics at high latitudes can provide insight into how these climatologically variable regions have affected avian lineages. Waterfowl also represent an unusual exception to the male-biased philopatry and female-biased dispersal that is the prevalent pattern in other birds (Rohwer and Anderson 1988, Andersen et al. 1992). Pair formation in most Holarctic migratory ducks occurs on the wintering grounds (McKinney 1992, Oring and Sayler 1992), where considerable mixing of birds from different nesting areas can occur; yet mated pairs frequently return to the female's natal or prior nesting area, such that most gene flow in Northern Hemisphere waterfowl is thought to be malemediated. Maternally inherited mitochondrial DNA (mtDNA) is thus an excellent tool for phylogeographic studies of waterfowl, though it likely underestimates nuclear gene flow for most species.

The Mallard (Anas platyrhynchos) is the most numerous and well-known waterfowl species with a Holarctic distribution and thus serves as a model for waterfowl studies in the Holarctic. The Mallard's breeding range in the Palearctic extends from the British Isles and North Africa, through Europe and Russia, to the Pacific coast from the Kamchatka Peninsula to northern Japan and northeastern China (Shevareva 1968, Johnsgard 1978, Drilling et al. 2002). In the Nearctic, the species primarily breeds in the western and central parts of North America. Most Mallards are migratory, and spring and fall flights can exceed many thousands of kilometers. However, many populations in temperate Western Europe and North America are also resident where open water is available year-round.

Mallards are also noteworthy because they have hybridized extensively with other closely related species worldwide. After being introduced into Australia and New Zealand, Mallards hybridized with the Grey Duck (A. superciliosa; Braithwaite and Miller 1975, Gillespie 1985). Eastward expansion of Mallards into American Black Duck (A. rubripes) habitat in North America has resulted in an increase in the frequency of ducks showing hybrid Mallard χ American Black Duck plumage characteristics and a decline in American Black Duck numbers (Brodsky and Weatherhead 1984, D'Eon et al. 1994). In addition, the endemic Hawaiian Duck (A. wyviUiana) has hybridized with Mallards on the island of Oahu (Browne et al. 1993). Hybrids between Mallard and Mottled Duck (A. fulvigula) in North America (Mazourek and Gray 1994) and Mallard and Eastern Spot-billed Duck (A. zonorhyncha) in the Russian Far East have also been documented (Zhuravlev et al. 2002).

The population genetic structure of Mallards has not been studied adequately, particularly for Eurasian populations. Seasonal migrations and potential for high rates of gene flow without simple geographic directionality suggest that Mallard populations may show very little geographic structure. On the other hand, Shevareva (1968) identified nine Mallard populations in the territory of the former Soviet Union using banding records. In addition to providing insight into how strong seasonality, concordant seasonal migration, and historical processes have affected Holarctic avian lineages, knowledge of Mallard population structure and distribution is necessary to develop measures for management, because the Mallard is the most popular game duck in Eurasia and North America.