Sergei V. Drovetski

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

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 (ΦST = 0.4112–0.4956) but possessed little genetic structure within the Old World continental area (ΦST = 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 (ΦST = 0.0728–0.1461, P < 0.05). Mallards inhabit the Aleutian Islands year-round, so these insular populations may be isolated from Asian and North American populations that occur in the Aleutian Islands only during migration. Overall weak phylogeographic structure and low genetic differentiation within Asia, and between Asia and North America when only group A haplotypes were evaluated, is probably explained by large long-term population sizes and significant intra-continental dispersal. The coexistence and nonrandom distribution of two divergent mtDNA haplotype lineages in Alaska, the Aleutian Islands, and the Primorye region of North Asia, but not in Western Russia or elsewhere in North Asia, is consistent with historical and contemporary hybridization and incomplete sorting of A and B mtDNA haplotype lineages in Mallards and closely related species inhabiting the Old World and New World.

Mitochondrial phylogeographies of five widespread Eurasian bird species

Five species of Eurasian birds displayed a range of mitochondrial DNA phylogeographic structures, including a single widespread lineage (common sandpiper), two geographically unsorted and closely related lineages (long-tailed tit), three partially overlapping closely related lineages (reed bunting), and two divergent geographically isolated lineages that rival species distinction (red-breasted flycatcher and skylark). Only the red-breasted flycatcher and the skylark displayed congruent phylogeographic structures. These five species represent different stages of diversification and speciation. There was little evidence that natural selection had influenced mitochondrial NADH dehydrogenase subunit 2 (ND2) sequences. In several instances, population growth was hypothesized, based on haplotype distributions within populations.

Barn swallows before barns: population histories and intercontinental colonization.

The barn swallow (Hirundo rustica) is one of most widely distributed swallows, owing in part to its recent switch from natural nest sites to human structures. We conducted phylogenetic analysis of mitochondrial (mt) and nuclear DNA to explore the recent evolutionary history of this species. Strongly supported mtDNA clades corresponded to Europe, Asia and North America plus the Baikal region of Asia. Analysis of sequence data from a sex-linked nuclear gene was unable to recover the phylogenetic splits in the mtDNA tree, confirming that the main clades evolved recently. The phylogenetic pattern suggests that the ancestral area of the barn swallow was the holarctic; most divergence events are consistent with vicariance. Most unexpectedly, analyses show that barn swallows from North America colonized the Baikal region in the recent past (one fixed substitution). This dispersal direction is opposite of that for most nearctic–palearctic taxon exchanges. Although this invasion was envisioned to coincide with the appearance of new types of human dwelling in the Baikal region, calibration of molecular divergence suggests an older dispersal event. A recent history of gene flow within the main palearctic clades is consistent with range and population expansion owing to new nesting opportunities provided by human settlements. Contrary to expectation, populations in North America appear historically larger and more stable than those in the palearctic. The Baikal population apparently has not increased greatly since colonization.

Influence of the trailing-edge notch on flight performance of galliforms

ABsmAcT.-Trailing-edge notches, formed by shortened first secondaries, characterize the wings of most galliforms. I investigated the function of these notches with comparative measurements of notch size taken from extended-wing specimens and with experimental studies of model wings of four representative species. Pheasants, quail, and turkeys, all of which use flight to escape predators, have wide wings and deep notches. Grouse with dark flight muscles have long, narrow wings with small trailing-edge notches and typically fly relatively long distances from one foraging site to another. Grouse with light colored flight muscles have short, broad wings with large trailing-edge notches and mostly fly from ground to canopy or from branch to branch to reach their food. Model wings of two pairs of galliforms with different wing shapes were used in the experiments. White-tailed Ptarmigan (Lagopus leucurus) and Sage Grouse (Centrocercus urophasianus) have small notches, high aspect ratios, relatively heavy wing loadings, low maximum lift coefficients, and dark pectoral muscles. In contrast, Wild Turkey (Meleagris gallopavo) and California Quail (Callipepla californica) have deep notches, low aspect ratios, relatively light wing loadings, high lift coefficients, and light colored pectoral muscles. Experiments using model wings in a water flow tunnel show that the trailing-edge notch increases the maximum lift-to-drag ratio and stabilizes airflow around the wing, but reduces the maximum lift coefficient. Thus, the trailing-edge notch increases performance in vertical and slow flight but reduces efficiency in level flight. Such a function is consistent with the suite of differences these birds show in muscle color, wing shape, and predominant mode of flight. Received 17 November 1995, accepted 27 February 1996.