Sarah A. Sonsthagen

Parallel evolution in the major haemoglobin genes of eight species of Andean waterfowl

Theory predicts that parallel evolution should be common when the number of beneficial mutations is limited by selective constraints on protein structure. However, confirmation is scarce in natural populations. Here we studied the major haemoglobin genes of eight Andean duck lineages and compared them to 115 other waterfowl species, including the bar‐headed goose (Anser indicus) and Abyssinian blue‐winged goose (Cyanochen cyanopterus), two additional species living at high altitude. One to five amino acid replacements were significantly overrepresented or derived in each highland population, and parallel substitutions were more common than in simulated sequences evolved under a neutral model. Two substitutions evolved in parallel in the αA subunit of two (Ala‐α8) and five (Thr‐α77) taxa, and five identical βA subunit substitutions were observed in two (Ser‐β4, Glu‐β94, Met‐β133) or three (Ser‐β13, Ser‐β116) taxa. Substitutions at adjacent sites within the same functional protein region were also observed. Five such replacements were in exterior, solvent‐accessible positions on the A helix and AB corner of the αA subunit. Five others were in close proximity to inositolpentaphosphate binding sites, and two pairs of independent replacements occurred at two different α1β1 intersubunit contacts. More than half of the substitutions in highland lineages resulted in the acquisition of serine or threonine (18 gains vs. 2 losses), both of which possess a hydroxyl group that can hydrogen bond to a variety of polar substrates. The patterns of parallel evolution observed in these waterfowl suggest that adaptation to high‐altitude hypoxia has resulted from selection on unique but overlapping sets of one to five amino acid substitutions in each lineage.

Gene flow and genetic characterization of Northern Goshawks breeding in Utah

Abstract Adult movement and natal dispersal data demonstrate that Northern Goshawks (Accipiter gentilis) are able to travel over long distances, suggesting a large functional population. However, these data are unable to determine whether these movements contribute to gene flow among adjacent breeding areas. We used eight microsatellite DNA loci and mitochondrial DNA control-region sequence data to assess population structure of Northern Goshawks breeding in Utah. Goshawks had moderate levels of genetic variation at microsatellite loci (observed heterozygosity = 50%), similar to levels found in other medium-sized, highly mobile birds. Overall estimates of interpopulation variance in microsatellite alleles (FST = 0.011) and mtDNA haplotypes (ΦST = 0.126) were low and not significantly different from zero. Pairwise population comparisons using microsatellite markers revealed no differentiation among sampled sites, indicating that the functional population extends beyond Utah. However, pairwise population analyses of mtDNA uncovered a single case of differentiation between goshawks inhabiting Ashley National Forest, in northeastern Utah, and Dixie National Forest, in southwestern Utah. Low levels of population structuring observed in mtDNA between the two forests may be due to the smaller effective population size sampled by mtDNA, a cline of haplotypes across the West, or the presence of a contact zone between A. g. atricapillus and goshawks of southern Arizona and the Mexican Plateau. Flujo Genético y Caracterización Genética de Accipiter gentilis Reproduciéndose en Utah Resumen. Datos sobre el movimiento de los adultos de Accipter gentilis y la dispersión natal demuestran que A. gentilis es capaz de viajar largas distancias, lo que sugiere una gran población funcional. Sin embargo, dichos estudios no son capaces de determinar si estos movimientos contribuyen al flujo genético entre las áreas de reproducción. En este estudio se utilizaron ocho loci de microsatélites de ADN y secuencias de la región control del ADN mitocondrial para estimar la estructura poblacional de la unidad reproductiva de A. gentilis en Utah. Este halcón presentó niveles intermedios de variación genética en loci de microsatélites (heterocigosidad observada = 50%), similares a los niveles encontrados en otras aves de tamaño medio con gran dispersión. La estimación total inter-poblacional de la varianza en alelos de microsatélites (FST = 0.011) y haplotipos de ADNmt (ΦST = 0.126) resultaron ser bajas y no significativamente diferentes de cero. Las comparaciones entre pares de poblaciones utilizando marcadores de microsatélites no mostraron diferencias entre los sitios muestreados, indicando que la población funcional se extiende más allá de Utah. Sin embargo, el análisis con ADNmt entre pares de poblaciones mostró en un sólo caso una diferenciación entre la población de A. gentilis que habita en el Bosque Nacional Ashley al noreste de Utah y la población de A. gentilis del Bosque Nacional Dixie, al sureste de Utah. Los niveles bajos de estructura poblacional observados con ADNmt entre los dos bosques pueden deberse a un bajo tamaño poblacional efectivo muestreado con ADNmt, a una disminución de haplotipos hacia el oeste o a la presencia de una zona de contacto entre A. g. atricapillus y Accipiter gentilis del sureste de Arizona y la meseta Mexicana.

Implications of the Circumpolar Genetic Structure of Polar Bears for Their Conservation in a Rapidly Warming Arctic

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1–3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will allow polar nations to proactively adjust conservation actions to continuing decline in sea-ice habitat.

Dispersal of H9N2 influenza A viruses between East Asia and North America by wild birds

Samples were collected from wild birds in western Alaska to assess dispersal of influenza A viruses between East Asia and North America. Two isolates shared nearly identical nucleotide identity at eight genomic segments with H9N2 viruses isolated from China and South Korea providing evidence for intercontinental dispersal by migratory birds.

Do common eiders nest in kin groups? Microgeographic genetic structure in a philopatric sea duck

We investigated local genetic associations among female Pacific common eiders (Somateria mollissima v‐nigrum) nesting in a stochastic Arctic environment within two groups of barrier islands (Simpson Lagoon and Mikkelsen Bay) in the Beaufort Sea, Alaska. Nonrandom genetic associations were observed among nesting females using regional spatial autocorrelation analyses for distance classes up to 1000 m in Simpson Lagoon. Nearest‐neighbour analyses identified clusters of genetically related females with positive lr values observed for 0–13% and 0–7% of the comparisons in Simpson Lagoon and Mikkelsen Bay, respectively, across years. These results indicate that a proportion of females are nesting in close proximity to more genetically related individuals, albeit at low frequency. Such kin groupings may form through active association between relatives or through natal philopatry and breeding site fidelity. Eiders nest in close association with driftwood, which is redistributed annually by seasonal storms. Yet, genetic associations were still observed. Microgeographic structure may thus be more attributable to kin association than natal philopatry and site fidelity. However, habitat availability may also influence the level of structure observed. Regional structure was present only within Simpson Lagoon and this island group includes at least three islands with sufficient driftwood for colonies, whereas only one island at Mikkelsen Bay has these features. A long‐term demographic study is needed to understand more fully the mechanisms that lead to fine‐scale genetic structure observed in common eiders breeding in the Beaufort Sea.

Hierarchical Spatial Genetic Structure of Common Eiders (Somateria mollissima) Breeding Along a Migratory Corridor

ABSTRACT. Documentation of spatial genetic discordance among breeding populations of Arctic-nesting avian species is important, because anthropogenic change is altering environmental linkages at micro- and macrogeographic scales. We estimated levels of population subdivision within Pacific Common Eiders (Somateria mollissima v-nigrum) breeding on 12 barrier islands in the western Beaufort Sea, Alaska, using molecular markers and capture—mark—recapture (CMR) data. Common Eider populations were genetically structured on a microgeographic scale. Regional comparisons between populations breeding on island groups separated by 90 km (Mikkelsen Bay and Simpson Lagoon) revealed structuring at 14 microsatellite loci (F ST = 0.004, P < 0.01), a nuclear intron (F ST = 0.022, P = 0.02), and mitochondrial DNA (&PHgr;ST = 0.082, P < 0.05). The CMR data (n = 34) did not indicate female dispersal between island groups. Concordance between genetic and CMR data indicates that females breeding in the western Beaufort Sea are strongly philopatric to island groups rather than to a particular island. Despite the apparent high site fidelity of females, coalescence-based models of gene flow suggest that asymmetrical western dispersal occurs between island groups and is likely mediated by Mikkelsen Bay females stopping early on spring migration at Simpson Lagoon to breed. Alternatively, late-arriving females may be predisposed to nest in Simpson Lagoon because of the greater availability and wider distribution of nesting habitat. Our results indicate that genetic discontinuities, mediated by female philopatry, can exist at microgeographic scales along established migratory corridors.

Genetic structure and viability selection in the golden eagle ( Aquila chrysaetos ), a vagile raptor with a Holarctic distribution

Molecular markers can reveal interesting aspects of organismal ecology and evolution, especially when surveyed in rare or elusive species. Herein, we provide a preliminary assessment of golden eagle (Aquila chrysaetos) population structure in North America using novel single nucleotide polymorphisms (SNPs). These SNPs included one molecular sexing marker, two mitochondrial markers, 85 putatively neutral markers that were derived from noncoding regions within large intergenic intervals, and 74 putatively nonneutral markers found in or very near protein-coding genes. We genotyped 523 eagle samples at these 162 SNPs and quantified genotyping error rates and variability at each marker. Our samples corresponded to 344 individual golden eagles as assessed by unique multilocus genotypes. Observed heterozygosity of known adults was significantly higher than of chicks, as was the number of heterozygous loci, indicating that mean zygosity measured across all 159 autosomal markers was an indicator of fitness as it is associated with eagle survival to adulthood. Finally, we used chick samples of known provenance to test for population differentiation across portions of North America and found pronounced structure among geographic sampling sites. These data indicate that cryptic genetic population structure is likely widespread in the golden eagle gene pool, and that extensive field sampling and genotyping will be required to more clearly delineate management units within North America and elsewhere.

HEAT PRODUCTION FROM FORAGING ACTIVITY CONTRIBUTES TO THERMOREGULATION IN BLACK-CAPPED CHICKADEES

Abstract We measured metabolic heat production (H ˙m) of perching and foraging Black-capped Chickadees (Poecile atricapillus) to determine if the heat produced during foraging activity, or exercise thermogenesis, could replace thermoregulatory heat production requirements. H ˙m and activity of chickadees in winter were measured at ambient temperatures (Ta) ranging from −11.5° to 15.5°C. Mean activity amplitude recorded with an activity detector was significantly higher in foraging birds than perching birds. H ˙m did not vary significantly between perching and foraging birds, indicating that heat produced during foraging does substitute for heat produced by shivering for thermoregulation. Evaporative water loss and dry thermal conductance did not vary significantly between perching and foraging chickadees. These results suggest that heat produced from locomotor muscles during foraging activity substitutes for thermoregulatory requirements in glean-and-hang foraging species, such as chickadees, as well as in ground-foraging birds.

Spatial genetic structure and asymmetrical gene flow within the Pacific walrus

Abstract Pacific walruses (Odobenus rosmarus divergens) occupying shelf waters of Pacific Arctic seas migrate during spring and summer from 3 breeding areas in the Bering Sea to form sexually segregated nonbreeding aggregations. We assessed genetic relationships among 2 putative breeding populations and 6 nonbreeding aggregations. Analyses of mitochondrial DNA (mtDNA) control region sequence data suggest that males are distinct among breeding populations (ΦST = 0.051), and between the eastern Chukchi and other nonbreeding aggregations (ΦST = 0.336–0.449). Nonbreeding female aggregations were genetically distinct across marker types (microsatellite FST = 0.019; mtDNA ΦST = 0.313), as was eastern Chukchi and all other nonbreeding aggregations (microsatellite FST = 0.019–0.035; mtDNA ΦST = 0.386–0.389). Gene flow estimates are asymmetrical from St. Lawrence Island into the southeastern Bering breeding population for both sexes. Partitioning of haplotype frequencies among breeding populations suggests that individuals exhibit some degree of philopatry, although weak. High levels of genetic differentiation among eastern Chukchi and all other nonbreeding aggregations, but considerably lower genetic differentiation between breeding populations, suggest that at least 1 genetically distinct breeding population remained unsampled. Limited genetic structure at microsatellite loci between assayed breeding areas can emerge from several processes, including male-mediated gene flow, or population admixture following a decrease in census size (i.e., due to commercial harvest during 1880–1950s) and subsequent recovery. Nevertheless, high levels of genetic diversity in the Pacific walrus, which withstood prolonged decreases in census numbers with little impact on neutral genetic diversity, may reflect resiliency in the face of past environmental challenges.

Speciation, Subspecies Divergence, and Paraphyly in the Cinnamon Teal and Blue-Winged Teal

Abstract. Divergent selection can lead to substantial morphological and behavioral differences despite slight differentiation in neutral genetic variation. We examined the evolutionary history of two closely related waterfowl, the Cinnamon Teal (Anas cyanoptera) and Blue-winged Teal (A. discors), that are morphologically distinct but paraphyletic in mitochondrial DNA (mtDNA) and share allozyme alleles. Sequences of mtDNA and two nuclear introns revealed that North American Cinnamon Teal (n = 70) and Blue-winged Teal (n = 76) are characterized by high genetic diversity, a large effective population size, and recent population expansion. In contrast, South American Cinnamon Teal (n = 102) have less genetic diversity and a smaller effective population size that has been more stable. We found 91 unique mtDNA haplotypes, only a few of which were shared by the two species or the three subspecies of the Cinnamon Teal, but the haplotypes were intermixed in a polyphyletic relationship, and we found no diagnostic phylogroups. Moreover, populations were more strongly differentiated in mtDNA (&PHgr;ST = 0.41) than in the nuclear introns (&PHgr;ST = 0.04–0.06). Analyses of isolation with migration indicated that sharing of haplotypes and alleles in the two continents is more likely attributable to incomplete lineage sorting than to gene flow, whereas estimates within each continent yielded higher migration rates. The oldest divergence was between North American Cinnamon Teal and the other taxa, whereas the Blue-winged Teal likely split from South American Cinnamon Teal more recently. Considerable overlap in confidence intervals for these divergences, however, suggests that these taxa diversified rapidly.