Biomedical subjects

K A Hobson

Publications and source records attributed to K A Hobson.

At least 19 recordsLinked to original sources

PubMed2006

Chernobyl as a population sink for barn swallows: tracking dispersal using stable-isotope profiles.

Stable-isotope profiles of feathers can reveal the location or habitat used by individual birds during the molting period. Heterogeneity in isotope profiles will reflect heterogeneity in molt locations, but also heterogeneity in breeding locations, because spatial heterogeneity in molt locations will be congruent with spatial heterogeneity in breeding locations in species with high connectivity between breeding and molting sites. We used information on the congruence of spatial heterogeneity in molt and breeding location to study population processes in Barn Swallows (Hirundo rustica) from a region. near Chernobyl, Ukraine, that has been radioactively contaminated since 1986; from an uncontaminated control region near Kanev, Ukraine; and from a sample of pre-1986 museum specimens used to investigate patterns prior to the nuclear disaster at Chernobyl, from both regions. Previous studies have revealed severe reductions in Barn Swallow reproductive performance and adult survival in the Chernobyl region, implying that the population is a sink and unable to sustain itself. Female Barn Swallows are known to disperse farther from their natal site than males, implying that female stable-isotope profiles should tend to be more variable than profiles of males. However, if the Barn Swallows breeding at Chernobyl are not self-sustaining, we would expect males there also to originate from a larger area than males from the control region. We found evidence that the sample of adult Barn Swallows from the Chernobyl region was more isotopically heterogeneous than the control sample, as evidenced from a significant correlation between feather sigma13C and sigma15N values in the control region, but not in the Chernobyl region. Furthermore, we found a significant difference in feather sigma15N values between regions and periods (before and after 1986). When we compared the variances in sigma13C values of feathers, we found that variances in both sexes from post-1986 samples from Chernobyl were significantly larger than variances for feather samples from the control region, and than variances for historical samples from both regions. These findings suggest that stable-isotope measurements can provide information about population processes following environmental perturbations.

Aging↗

PubMed2005

Using stable isotopes to study resource acquisition and allocation in procellariiform seabirds.

Some procellariiform seabirds use a dual strategy for provisioning their chicks by alternating short (ST) and long (LT) foraging trips. Parent birds gain mass during LT but they lose mass while increasing the chick feeding frequency during ST. Self-feeding during LT is crucial for the success of ST because firstly most of the energy used during ST is likely to be derived from the energy stored during LT and secondly self-feeding during ST is presumed to be negligible. Self-feeding by adult procellariiforms is thus a key issue to understand allocation processes but it is still poorly known. We tested these predictions by using the stable isotope (delta(15)N and delta(13)C) technique on birds' plasma and prey with the short-tailed shearwater Puffinus tenuirostris breeding at Tasmania as a model. Parent shearwaters returning to the colony after a LT have an Antarctic/subantarctic delta(13)C signature in their plasma (-23.8 per thousand), thus indicating that they fed in cold waters, far away from their breeding colony, for their own maintenance. Parent birds returning to the colony after a ST also have a distant Antarctic/subantarctic delta(13)C signature in their plasma (-24.3 per thousand), thus verifying that self-feeding is negligible during ST and that birds fast at that time, using energy stores built up in cold waters. Plasma delta(15)N values of adults (8.8 per thousand) indicates they mainly prey upon zooplankton-eating organisms, probably mesopelagic myctophid fishes. A simple isotopic mixing model estimates that they consume by mass 87% myctophids and 13% subantarctic krill when self-feeding. Finally and as expected, the carbon isotopic signature of chick plasma (-22.2 per thousand) was intermediate between those of high- and low-latitude marine organisms and is thus in agreement with chicks being fed with a large diversity of prey species caught by adult birds from Antarctic to Tasmanian waters. One main consequence of this system is that reproduction of a Tasmanian species is controlled by resources available at great distances from the breeding colony that drive allocation decisions of parent birds.

Animal Migration↗

PubMed2005

Stable isotope and band-encounter analyses delineate migratory patterns and catchment areas of white-throated sparrows at a migration monitoring station.

The Canadian Migration Monitoring Network consists of several fixed migration monitoring stations (MMS) that apply constant-effort protocols to track changes in the abundance of migratory birds. Such monitoring will be important for tracking long-term population trends of songbirds, especially for species breeding in remote areas such as the North American boreal forest. The geographical catchment sampled by individual MMS, however, remains largely unknown. Here, we used hydrogen isotope measurements (deltaD) of feathers of white-throated sparrows (Zonotrichia albicollis) moving through Delta Marsh MMS in Manitoba, Canada, to determine both wintering and breeding ground catchment areas monitored by this station. The deltaD of tail feathers, collected from spring and fall migrants delineated previous breeding or natal latitudes, ranging from the northern to the southern extremes of the western boreal forest. The deltaD values of head feathers grown on the wintering grounds and collected during spring migration revealed that individuals wintered in a broad region of the southeastern United States. The isotope data showed no relationship between estimated breeding/natal and wintering latitudes of white-throated sparrow populations. Stable isotope data provided little information on longitude. Band-encounter analyses, however, indicated a clear east-west segregation of these sparrows across Canada, supporting connectivity among breeding/natal and wintering longitudes over the entire scale of this species' range. Isotope analyses of multiple feather types representing different periods and geographic regions of the annual cycle can provide key information on migratory connectivity for species moving through dedicated MMS.

Animal Migration↗

PubMed2005

Changes in mercury and cadmium concentrations and the feeding behaviour of beluga (Delphinapterus leucas) near Somerset Island, Canada, during the 20th century.

Beluga (Delphinapterus leucas) continues to be an important food species for Arctic communities, despite concerns about its high mercury (Hg) content. We investigated whether Hg and cadmium (Cd) concentrations had changed during the 20th century in beluga near Somerset Island in the central Canadian Arctic, using well-preserved teeth collected from historical sites (dating to the late 19th century and 1926-1947) and during subsistence hunts in the late 1990s. Mercury concentrations in both historical and modern teeth were correlated with animal age, but 1990s beluga exhibited a significantly more rapid accumulation with age than late 19th century animals, indicating that Hg concentrations or bioavailability in their food chain had increased during the last century. The geometric mean tooth Hg concentration in modern 30 year old animals was 7.7 times higher than in the late 19th century, which corresponds to threefold higher concentrations in muktuk and muscle. Teeth from 1926 to 1947 were similar in Hg content to the late 19th century, suggesting that the increase had occurred sometime after the 1940s. In contrast, tooth Cd was not correlated with animal age and decreased during the last 100 years, indicating that anthropogenic Cd was negligible in this population. Late 19th century beluga displayed a greater range of prey selection (tooth delta15N values: 15.6-20.5 per thousand) than modern animals (delta15N: 17.2-21.1 per thousand). To prevent this difference from confounding the temporal Hg comparison, the Hg-age relationships discussed above were based on historical animals, which overlapped isotopically with the modern group. Tooth delta13C also changed to isotopically more depleted values in modern animals, with the most likely explanation being a significant shift to more pelagic-based feeding. Industrial Hg pollution is a plausible explanation for the recent Hg increase. However, without further investigation of the relationship between the range exploitation of modern beluga and their possible exposure to regional marine food chains with (naturally) higher Hg contents than their historical counterparts, we cannot unequivocally conclude that the increase was anthropogenically driven.

Animals↗

PubMed2004

Baleen as a biomonitor of mercury content and dietary history of North Atlantic minke whales (Balaenopetra acutorostrata): combining elemental and stable isotope approaches.

Baleen is an incrementally-growing tissue of balaenopteran whales which preserves relatively well over time in museums and some archeological sites, and, therefore might be useful for studies examining long-term changes of metal levels in whales. This study examined Hg and stable C and N isotopic composition of baleen plates of the North Atlantic minke whale (Balaenoptera acutorostrata), which continues to be a food source for people in Greenland and elsewhere. We compared the Hg levels and stable isotopes of major tissues (kidney, liver and muscle) with those of baleen plates to see whether baleen could be used as a biomonitor of variations of Hg intake and diet both between individuals and within individuals over time. Mercury was significantly correlated with concentrations in all tissues (kidney, liver and muscle). Stable C and N isotopes in baleen were generally similar to those of muscle, which reflects the recent (approximately one month) feeding of the whale, but in some individuals there were significant differences between baleen and muscle. Sectioning of baleen into 1 cm longitudinal increments showed that these differences were due to marked dietary shifts by some individuals over time that had been recorded in the baleen but were lost from the muscle record. Whole baleen C and N isotopes were better correlated with tissue Hg levels, suggesting that baleen may provide a more reliable indicator of long-term average diet, which in turn may be better related to Hg accumulation in tissues than the shorter-term diet record contained in muscle.

Animals↗

PubMed2004

Regional and inter annual patterns of heavy metals, organochlorines and stable isotopes in narwhals (Monodon monoceros) from West Greenland.

Samples of 150 narwhals obtained in different years from two West Greenland areas, Avanersuaq and Uummannaq, were compared for concentrations of and regional differences in heavy metals and organochlorines and stable-carbon and nitrogen isotopes. Cadmium, Hg, and Se concentrations increased in the first 3-4 years of the animal's life, after which no dependence on age was observed. Females had significantly higher concentrations of Cd in all tissues and of Hg and Se in liver than males. No consistent difference in metal levels between narwhals from Avanersuaq and Uummannaq was found. Year-to-year variation in metal levels at one location was larger than the geographical variation. Metal levels were within the range of previous published results for narwhals from Arctic Canada. Organochlorine (OC) concentrations in blubber of narwhals were dependent on age and sex. Females showed decreasing OC concentration in the first 8-10 years, while for males increases were detected in the first few years of life, after which the concentrations became stable. Few statistical differences in mean OC concentrations among individuals were observed. However, narwhals from Avanersuaq in 1993 had the lowest levels, indicating a temporal decrease of SigmaPCBs. SigmaPCBs, DDTs, HCHs and toxaphenes seem to be at similar levels in West Greenland and Arctic Canada, which can be explained by the close winter distributions of populations as well as large ranges in concentrations, time span, number of analyses and the size/age composition of the data. PCB and DDT concentrations in West Greenland narwhals were half those found in East Greenland and Svalbard. Stable-carbon isotope ratios in muscle of 150 narwhals showed a decreasing trend in the first year when they gradually reduced their dependency on mother's milk, after which they became relatively stable. delta15 N values were significantly higher in samples from Uummannaq in 1993 compared to samples from Avanersuaq in 1984 and 1985 indicating that the diet of the narwhals in Uummannaq was at a higher trophic level. However, only a few significant correlations were found between stable isotope ratios and metal and OC concentrations.

Age Factors↗

PubMed2003

Comparative equilibration and online technique for determination of non-exchangeable hydrogen of keratins for use in animal migration studies.

Stable hydrogen-isotope ratios (deltaD) of keratin provide a novel means for tracking geographical movements of birds and other species. Here we describe a rapid, low cost, analytical approach to facilitate online continuous-flow isotope-ratio mass spectrometry (CF-IRMS) deltaD analyses of keratins (120-160 samples per day) through the use of calibrated keratin working standards and "comparative equilibration" to correct for the effects of moisture on exchangeable hydrogen. It is anticipated that this analytical approach and CF-IRMS will greatly aid in providing cost effective and directly comparable deltaD results on keratins and feathers among various laboratories and researchers involved in animal migration studies.

Animals↗

PubMed2002

Persistent organochlorine contaminants and enantiomeric signatures of chiral pollutants in ringed seals (Phoca hispida) collected on the east and west side of the Northwater Polynya, Canadian Arctic.

To examine the influence of diet and age on organochlorine contaminant (OC) concentrations in two closely related ringed seal (Phoca hispida) populations enantiomeric fractions (EFs) of chiral contaminants and stable isotopes of nitrogen (delta15N) and carbon (delta13C) were measured along with OCs in ringed seals collected from the east and west side of the Northwater Polynya. Seals from these two locations were feeding at the same trophic level based on delta15N values in muscle but had slightly different sources of carbon based on delta13C measurements in muscle. After removing the influence of age, sex, and blubber thickness, OC concentrations did not vary between ringed seals from the east and west side of the polynya. SigmaPCB, SigmaDDT, and Sigmachlordane were found to increase with age for both male and female seals. The inclusion of older (>20 years) female seals, which may have a reduced reproductive effort, may influence the relationships in females. Stable isotopes failed to describe OC concentrations in ringed seals suggesting that diet was not a major factor in variation of OC concentrations within this ringed seal population. Cis- and trans-chlordane, oxychlordane, and heptachlor epoxide were all nonracemic in the ringed seal blubber but did not vary with age, sex, or collection site. Alpha-HCH appeared racemic (enantiomeric fraction = 0.50 +/- 0.01) in the seals, although this EF is different than those previously observed in their prey species, and was found to vary significantly with age. EF values in the ringed seals varied considerably from other Arctic marine mammals and seabirds, providing addition evidence that the type(s) and characteristic(s) of the enzymes involved in biotransformation of chiral OCs vary between these organisms.

Adipose Tissue↗

PubMed2002

Contaminant residues in seabird eggs from the Canadian Arctic. II. Spatial trends and evidence from stable isotopes for intercolony differences.

Eggs of glaucous gulls (Larus hyperboreus), black-legged kittiwakes (Rissa tridactyla), thick-billed murres (Uria lomvia) and black guillemots (Cepphus grylle) were collected from several sites throughout the Canadian Arctic. Samples were analyzed for organochlorines as well as mercury and selenium. Glaucous gulls breeding at sites in the High Arctic showed higher levels of organochlorine contamination than those in the western Low Arctic. This was likely due to dietary differences among colonies as suggested by stable isotope data, although different overwintering areas may also play a role. Levels of sigmaPCB, sigmaDDT, sigmaCHLOR, sigmaCBz and dieldrin were significantly lower in thick-billed murres from Prince Leopold Island in the High Arctic compared with colonies in the eastcrn Low Arctic. This difference was likely due to the combined effects of different atmospheric deposition patterns in the High and Low Arctic and different overwintering areas since murres from Prince Leopold Island may winter farther north than murres from the other colonies sampled. Eggs from colonies at higher latitudes generally contained higher concentrations of mercury. The trophic and dietary differences/similarities suggested by stable-nitrogen and carbon isotope data in this study were useful in explaining the spatial patterns of contaminant concentrations observed among colonies of seabirds such as the glaucous gull and the black-legged kittiwake where variation in latitudinal atmospheric deposition patterns and different overwintering grounds did not appear to be confounding factors.

Animals↗

PubMed2001

Hexachlorocyclohexane (HCH) isomers and chiral signatures of alpha-HCH in the Arctic marine food web of the Northwater Polynya.

Concentrations of hexachlorocyclohexane (HCH) isomers (alpha, beta, and gamma) and enantiomer fractions (EFs) of alpha-HCH were determined in the Northwater Polynya Arctic marine food web. Relative food web structure was established using trophic level models based on organic delta 15N values. Concentrations of HCH in the samples collected, including water, sediment, benthic invertebrates (four species), pelagic zooplankton (six species), Arctic cod, seabirds (seven species), and ringed seal, were in the range previously reported for the Canadian Arctic. The relative proportion of the HCH isomers varied across the food web and appeared to be related to the biotransformation capacity of each species. For invertebrates and fish the biomagnification factors (BMFs) of the three isomers were > 1 and the proportion of each isomer and the EFs of alpha-HCH were similar to water, suggesting minimal biotransformation. Seabirds appear to readily metabolize gamma- and alpha-HCH based on low BMFs for these isomers, high proportions of beta-HCH (62-96%), and high EFs (0.65-0.97) for alpha-HCH. The alpha- and beta-HCH isomers appear to be recalcitrant in ringed seals based on BMFs > 1 and near racemic EFs for alpha-HCH. The beta isomer appears to be recalcitrant in all species examined and had an overall food web magnification factor of 3.9. EFs of alpha-HCH and the proportion of beta-HCH in sigma-HCH in the food web were highly correlated (r2 = 0.92) suggesting that EFs were a good indicator of a species capability to biotransform alpha-HCH.

Animals↗

PubMed2001

A stable-isotope approach to delineate geographical catchment areas of avian migration monitoring stations in North America.

Migration monitoring stations (MMSs) were established to provide information on population trends of North American passerines. However, apart from inferring general origins of birds, there has been no way to delineate geographical catchment areas sampled by MMSs. The ability to resolve MMS catchment areas would greatly enhance our ability to link and constrain population declines to specific geographical areas and thereby focus conservation efforts. Here, we utilize stable-hydrogen (delta D) and carbon (delta 13C) isotope values of rectrices of fall hatch-year (HY) and spring adult after-second year (ASY) Swainson's Thrush (Catharus ustulatus) moving through two MMSs in Canada to determine natal and molting catchment areas for those stations. Stable-carbon isotope signatures provided no information on geographical origins of birds. Conversely, delta D signatures provided good latitudinal geographical control, and this was also supported by analysis of feathers from two other species, Gray-cheeked Thrush (Catharus minimus) and Harris' Sparrow (Zonotrichia querula), also known to breed and molt in northern regions. The delta D values of fall HY birds moving through Delta Marsh MMSs in Manitoba were more negative than those moving through Long Point MMSs in southern Ontario, clearly indicating more northwesterly origins. However, based on delta D values alone, both MMSs sampled birds from broad catchment regions of the Canadian Boreal forest. The interpolated catchment area of the Delta MMS encompassed northwest Manitoba to northwestern Alberta. The interpolated catchment area of the Long Point MMS extended from north central Ontario and Quebec and into western Canada. The delta D values of birds moving northward in spring suggested that most ASY Swainson's Thrush molted at more southerly locations than their breeding sites. We show the stable-hydrogen isotope approach may be employed to significantly improve conventional observational techniques for avian population monitoring, and that MMSs provide a reliable means of associating population productivity with regional conservation issues.

Animals↗

PubMed2001

Influence of chemical and biological factors on trophic transfer of persistent organic pollutants in the northwater polynya marine food web.

Persistent organic pollutants (POPs) and stable isotopes of nitrogen (delta 15N) were measured in zooplankton (6 species), a benthic invertebrate (Anonyx nugax), Arctic cod (Boreogadus saida), seabirds (6 species), and ringed seals (Phoca hispida) collected in 1998 in the Northwater Polynya to examine effects of biological and chemical factors on trophic transfer of POPs in an Arctic marine food web. Strong positive relationships were found between recalcitrant POP concentrations (lipid corrected) and trophic level based on stable isotopes of nitrogen, providing clear evidence of POP biomagnification in Arctic marine food webs. Food web magnification factors (FWMFs), derived from the slope of the POP--trophic level relationship, provided an overall magnification factor for the food web but over and underestimated biomagnification factors (BMFs) based on predator--prey concentrations in poikilotherms (fish) and homeotherms (seabirds and mammals), respectively. Greater biomagnification in homeotherms was attributed to their greater energy requirement and subsequent feeding rates. Within the homeotherms, seabirds had greater BMFs than ringed seals, consistent with greater energy demands in birds. Scavenging from marine mammal carcasses and accumulation in more contaminated winter habitats were considered important variables in seabird BMFs. Metabolic differences between species resulted in lower than expected BMFs, which would not be recognized in whole food web trophic level--POP relationships. The use of sigma POP groups, such as sigma PCB, is problematic because FWMFs and BMFs varied considerably between individual POPs. FWMFs of recalcitrant POPs had a strong positive relationship with log octanol--water partition coefficient (Kow). Results of this study show the utility of using delta 15N to characterize trophic level and trophic transfer of POPs but highlight the effects of species and chemical differences on trophic transfer of POPs that can be overlooked when a single magnification factor is applied to an entire food web.

Animals↗

PubMed2001

Chlordane components and metabolites in seven species of Arctic seabirds from the Northwater Polynya: relationships with stable isotopes of nitrogen and enantiomeric fractions of chiral components.

The Northwater Polynya (NOW) is a large area of year-round open water found in the high Arctic between Ellesmere Island and Greenland. NOW has high biological productivity compared with other arctic marine areas, and supports large populations of several seabird species. Seven species of seabirds, dovekie (Alle alle, DOVE), thick-billed murre (Uria lomvia, TBMU), black guillemot (Cepphus grylle, BLGU), black-legged kittiwake (Rissa tridactyla, BLKI), ivory gull (Pagophila eburnea, IVGU), glaucous gull (Larus hyperboreus, GLGU) and northern fulmar (Fulmaris glacialis, NOFU) were collected in May and June 1998 to determine chlordane concentrations in liver and fat and to examine species differences, relationships with stable isotopes of nitrogen, and enantiomeric fractions (EFs) of chiral components. sigma CHLOR concentrations varied over an order of magnitude among species, from a low of 176 +/- 19 ng/g (lipid corrected) in TMBU liver to a high of 3190 +/- 656 ng/g (lipid corrected) in NOFU liver. Lipid-corrected concentrations of chlordane did not vary between sex for any species or between fat and liver except for the DOVE, that had fat concentrations that were significantly greater than the liver. delta 15N values described a significant percentage of the variability of concentrations for most chlordane components, although less than what has been reported for whole food chains. Slopes of delta 15N versus concentration of chlordane components and sigma CHLOR were similar with the exception of those which were metabolized (trans-chlordane) or formed through biotransformation (oxychlordane). The relative proportions of chlordane components in seabirds were related to phylogeny; the procellariid (NOFU) had the greatest percentage of oxychlordane (> 70%), followed by the larids (BLKI, IVGU and GLGU; 40-50%) and the alcids (DOVE and BLGU; 10-20%). The exception was TBMU, an alcid, where oxychlordane made up > 40% of its chlordane. EFs of chiral components failed to predict concentration or trophic level, but did identify biotransformation differences between species and chlordane components. TBMU appeared to have a greater capacity to metabolize and eliminate chlordane, based on high proportions of oxychlordane, the highest EFs for oxychlordane and heptachlor epoxide, and a delta 15N-sigma CHLOR value which was well below the relationships developed for all seabird species.

Adipose Tissue↗

PubMed2001

Contaminant residues in seabird eggs from the Canadian Arctic. Part I. Temporal trends 1975-1998.

Concentrations of total mercury, selenium and a suite of organochlorine compounds were measured in eggs of thick-billed murres (Uria lomvia), northern fulmars (Fulmarus glacialis) and black-legged kittiwakes (Rissa tridactyla) collected on Prince Leopold Island in Lancaster Sound, Nunavut, Canada, between 1975 and 1998. Mercury levels in thick-billed murre and northern fulmar eggs increased significantly during this period while selenium concentrations decreased significantly in northern fulmar eggs. Mercury and selenium concentrations in black-legged kittiwake eggs exhibited no significant temporal trends. Concentrations of sigma PCB, sigma DDT and total chlorobenzenes decreased over time for all three species and there was a shift in the PCB congener pattern as the hexachlorobiphenyl fraction of sigma PCB increased and the lower chlorinated biphenyl fraction decreased. Total chlordane, dieldrin and mirex concentrations decreased in kittiwake eggs while no significant trends were observed for the other two species. Increases in sigma HCH levels were detected in thick-billed murre eggs but not in northern fulmar and black-legged kittiwake eggs. Levels of the beta-HCH isomer, however, increased significantly in murres and fulmars. Stable-nitrogen isotope analyses (delta 15N) indicate that the temporal trends observed for contaminant concentrations in eggs were not the result of shifts in trophic level. Changing deposition patterns of xenobiotic compounds over the summer and winter ranges of these birds provide a likely explanation for differing exposures through time.

Animals↗

PubMed2001

Renal structure in neotropical bats: using stable isotopes to explore relationships between diet and morphology.

The relationship between kidney structure and diet was examined in several species of bats from the tropics. The trophic level of the bats was determined by their stable nitrogen isotopic composition (delta15 N). The results indicate that the relative thickness of the renal medulla is directly related to the trophic level of the bats. Additionally, we also determined the relationship between body mass and kidney structure. Relative medullary thickness was reciprocally related to body mass in animalivorous bats but no relationship was found in phytophagous bats. Stable isotope analysis provided a quantitative approximation of diet to test its relationship with kidney structure.

Animals↗

PubMed2000

Phylogeography and genetic structure of northern populations of the yellow warbler (Dendroica petechia).

Phylogeographic patterns of intraspecific variation can provide insights into the population-level processes responsible for speciation and yield information useful for conservation purposes. To examine phylogeography and population structure in a migratory passerine bird at both continental and regional geographical scales, we analysed 344 bp of mitochondrial DNA (mtDNA) control region sequence from 155 yellow warblers (Dendroica petechia) collected from seven locations across Canada and from Alaska. There is a major subdivision between eastern (Manitoba to Newfoundland) and western (Alaska and British Columbia) populations which appears to have developed during the recent Pleistocene. Some localities within these two regions also differ significantly in their genetic composition, suggesting further subdivision on a regional geographical scale. Eastern and western birds form distinct phylogeographic entities and the clustering of all western haplotypes with two eastern haplotypes suggests that the western haplotypes may be derived from an eastern lineage. Analyses based on coalescent models support this explanation for the origin of western haplotypes. These results are consistent with important features of Mengel's model of warbler diversification. From a conservation perspective they also suggest that individual populations of migrant birds may form demographically isolated management units on a smaller scale than previously appreciated.

Alaska↗

PubMed2000

Limited differentiation in microsatellite DNA variation among northern populations of the yellow warbler: evidence for male-biased gene flow?

Comparisons of the patterns of differentiation among genetic markers with different modes of inheritance can provide insights into patterns of sex-biased dispersal and gene flow. Here, we compare the patterns of differentiation in six microsatellite loci among eight northern breeding populations of the yellow warbler (Dendroica petechia) with results obtained with mitochondrial DNA. Significant but low levels of differentiation (overall FST = 0.014; overall RST = 0.015) were present across all populations. The level of differentiation is substantially less than that observed in the same samples based on mitochondrial DNA control region variation. The presence of low population imbalance index values and significant isolation-by-distance relationships for both FST and RST suggests that these populations are at evolutionary equilibrium and that the high degree of similarity between populations may be due to high levels of male-biased gene flow. This suggests that there may be significant but previously unappreciated differences in the long-distance and/or episodic dispersal behaviour of males and females in these birds.

Alleles↗

PubMed1999

Influence of drinking water and diet on the stable-hydrogen isotope ratios of animal tissues.

Despite considerable interest in using stable-hydrogen isotope ratio (deltaD) measurements in ecological research, it was previously unknown whether hydrogen derived from drinking water, in addition to that derived from diet, contributed to the nonexchangeable hydrogen in animal tissues. We raised four experimental groups of quail (Coturnix coturnix japonica) from hatch on two isotopically distinct diets (mean nonexchangeable deltaD: -146 and -60 per thousand, Vienna Standard Mean Ocean Water Standard) and drinking waters (mean deltaD: -130 and +196 per thousand, Vienna Standard Mean Ocean Water Standard). Here we show that both dietary and drinking water hydrogen are incorporated into nonexchangeable hydrogen in both metabolically active (i.e., muscle, liver, blood, fat) and inactive (i.e., feather, nail) tissues. Approximately 20% of hydrogen in metabolically active quail tissues and 26-32% of feathers and nail was derived from drinking water. Our findings suggest environmental interpretations of deltaD values from modern and fossil animal tissues may need to account for potentially large isotopic differences between drinking water and food and require a good understanding of the physiological ecology of study organisms.

Adipose Tissue↗