Evolution and connectivity in the world-wide migration system of the mallard: Inferences from mitochondrial DNA

<p>Abstract</p> <p>Background</p> <p>Main waterfowl migration systems are well understood through ringing activities. However, in mallards (<it>Anas platyrhynchos</it>) ringing studies suggest deviations from general migratory trends and traditions in waterfowl. Furthermore, surprisingly little is known about the population genetic structure of mallards, and studying it may yield insight into the spread of diseases such as Avian Influenza, and in management and conservation of wetlands. The study of evolution of genetic diversity and subsequent partitioning thereof during the last glaciation adds to ongoing discussions on the general evolution of waterfowl populations and flyway evolution. Hypothesised mallard flyways are tested explicitly by analysing mitochondrial mallard DNA from the whole northern hemisphere.</p> <p>Results</p> <p>Phylogenetic analyses confirm two mitochondrial mallard clades. Genetic differentiation within Eurasia and North-America is low, on a continental scale, but large differences occur between these two land masses (<it>F</it>_ST= 0.51). Half the genetic variance lies within sampling locations, and a negligible portion between currently recognised waterfowl flyways, within Eurasia and North-America. Analysis of molecular variance (AMOVA) at continent scale, incorporating sampling localities as smallest units, also shows the absence of population structure on the flyway level. Finally, demographic modelling by coalescence simulation proposes a split between Eurasia and North-America 43,000 to 74,000 years ago and strong population growth (~100fold) since then and little migration (not statistically different from zero).</p> <p>Conclusions</p> <p>Based on this first complete assessment of the mallard's world-wide population genetic structure we confirm that no more than two mtDNA clades exist. Clade A is characteristic for Eurasia, and clade B for North-America although some representatives of clade A are also found in North-America. We explain this pattern by evaluating competing hypotheses and conclude that a complex mix of historical, recent and anthropogenic factors shaped the current mallard populations. We refute population classification based on flyways proposed by ornithologists and managers, because they seem to have little biological meaning. Our results have implications for wetland management and conservation, with special regard to the release of farmed mallards for hunting, as well as for the possible transmission of Avian Influenza by mallards due to migration.</p

ROTATION OF METHANE AND SILANE MOLECULES IN HELIUM DROPLETS

Author Institution: Chemistry Department, University of Southern California, Los Angeles,; California 90089; Terahertz Sensing and Imaging Laboratory, RIKEN; 519-1399 Aramaki; Aoba, Aoba-ku, Sendai, Miyagi, 980-0845, Japan; General Physics Institute, Vavilov str. 38, 117942 Moscow, Russia; Chemistry Department, University of Southern California, Los Angeles,; California 90089Spectra of the $\nu_3$ band of CH$_4$, CD$_4$, SiH$_4$ and SiD$_4$ embedded in helium droplets have been obtained. Band origins and rotational and centrifugal distortion constants were acquired. Comparison of the rotational constants of normal and deuterated molecules facilitates the studying of the dependence of the effective rotational constants in helium on the molecular moment of inertia. Large differences in the rotational constants of deuterated methane and silane in helium droplets, which have very similar rotational constants in gas-phase, are ascribed to a different interaction strength of the molecules with the helium environment

ROTATIONS OF CO2_2 AND CH4_4 ISOTOPOMERS IN HELIUM DROPLETS

Author Institution: Chemistry Department, University of Southern California, Los Angeles,; California 90089; Terahertz Sensing and Imaging Laboratory, RIKEN; 519-1399 Aramaki; Aoba, Aoba-ku, Sendai, Miyagi, 980-0845, Japan; General Physics Institute, Vavilov str. 38, 117942 Moscow, Russia; Chemistry Department, University of Southern California, Los Angeles,; California 90089The effect of isotopic substitution on molecular rotations of CO$_2$ and CH$_4$ have been studied via infrared spectroscopy in helium droplets. In the spectral region of $\nu_1 + \nu_3$ (3500 - 3700 cm$^{-1}$), rovibrational spectra of C$^{18}$O$_2$, C$^{16}$O$_2$ and C$^{16}$O$^{18}$O have been obtained showing significant participation of surrounding helium in rotations. In contrast, minor changes of rotational constants of CH$_4$ and CD$_4$ have been derived from the rovibrational spectra in the $\nu_3$ region (3020 and 2260 cm$^{-1}$ respectively). Rotational constants and band origins for all species have been determined. Coupling of molecular rotations with helium will be discussed

Widespread horizontal genomic exchange does not erode species barriers among sympatric ducks

BACKGROUND:The study of speciation and maintenance of species barriers is at the core of evolutionary biology. During speciation the genome of one population becomes separated from other populations of the same species, which may lead to genomic incompatibility with time. This separation is complete when no fertile offspring is produced from inter-population matings, which is the basis of the biological species concept. Birds, in particular ducks, are recognised as a challenging and illustrative group of higher vertebrates for speciation studies. There are many sympatric and ecologically similar duck species, among which fertile hybrids occur relatively frequently in nature, yet these species remain distinct.RESULTS:We show that the degree of shared single nucleotide polymorphisms (SNPs) between five species of dabbling ducks (genus Anas) is an order of magnitude higher than that previously reported between any pair of eukaryotic species with comparable evolutionary distances. We demonstrate that hybridisation has led to sustained exchange of genetic material between duck species on an evolutionary time scale without disintegrating species boundaries. Even though behavioural, genetic and ecological factors uphold species boundaries in ducks, we detect opposing forces allowing for viable interspecific hybrids, with long-term evolutionary implications. Based on the superspecies concept we here introduce the novel term "supra-population" to explain the persistence of SNPs identical by descent within the studied ducks despite their history as distinct species dating back millions of years.CONCLUSIONS:By reviewing evidence from speciation theory, palaeogeography and palaeontology we propose a fundamentally new model of speciation to accommodate our genetic findings in dabbling ducks. This model, we argue, may also shed light on longstanding unresolved general speciation and hybridisation patterns in higher organisms, e.g. in other bird groups with unusually high hybridisation rates. Observed parallels to horizontal gene transfer in bacteria facilitate the understanding of why ducks have been such an evolutionarily successful group of animals. There is large evolutionary potential in the ability to exchange genes among species and the resulting dramatic increase of effective population size to counter selective constraints