Genetic status of the wood stork (Mycteria americana) from the southeastern United States and the Brazilian Pantanal as revealed by mitochondrial DNA analysis.

The wood stork (Mycteria americana) is a colonial wading bird that inhabits the Neotropical region from the southeastern United States (US) to northern Argentina. The species is considered to be endangered in the US due to degradation of its foraging and breeding habitat. In other parts of its range, such as in the Brazilian Pantanal region, breeding populations of this species appear to be stable. We compared the levels of genetic variability and population structuring of the US and the Pantanal breeding populations using mitochondrial DNA (mtDNA) control region sequences. Twenty-seven haplotypes were identified among 88 wood stork samples collected from eight breeding colonies in the US and eight in the Pantanal. Patterns indicative of heteroplasmy were observed in 35.3% of the mtDNA sequences that were examined. Significantly higher levels of haplotype diversity were observed in the Pantanal samples compared to those from the US, suggesting that during the last century, demographic declines or a recent evolutionary bottleneck reduced the levels of mtDNA variability of the US population. Analyses of genetic structuring revealed non-significant genetic differentiation between these regions, indicating that either the populations were only recently separated or that gene flow continues to occur at low levels. Haplotype network analysis indicated low current levels of gene flow between populations that were closely related in the past.

Foraging ecology of the endangered wood stork recorded in the stable isotope signature of feathers.

Down feathers and regurgitant were collected from nestling wood storks (Mycteria americana) from two inland and two coastal breeding colonies in Georgia. The stable isotopic ratios of carbon (13C/12C) and nitrogen (15N/14N) in these materials were analyzed to gain insights into the natal origins of juvenile storks and the foraging activities of adults. Down feathers differed in δ13C between inland and coastal colonies, having average isotopic values that reflected the sources of carbon fixed in biomass at the base of the food web. Feathers from the inland colonies differed between colonies in δ15N, while those from the coastal colonies did not. These patterns primarily reflected the foraging activities of parent storks, with individuals capturing differing percentages of prey of distinct trophic status at each colony. Collectively, the carbon and nitrogen isotopic signatures of feather keratin were used to distinguish nestlings from each colony, except for instances where storks from different colonies foraged in common wetlands. The stable isotopic composition of food items in regurgitant was used to reconstruct the trophic structure of the ecosystems in which wood storks foraged. Predicted foraging activities based on the isotopic composition of keratin were generally consistent with the percentage of prey types (freshwater vs. saltwater and lower trophic level vs. upper trophic level consumer) observed in regurgitant, except for the coastal colony at St. Simons Island, where the δ13C of feathers strongly suggested that freshwater prey were a significant component of the diet. This inconsistency was resolved by aerial tracking of adults during foraging excursions using a fixed-wing aircraft. Observed foraging activities supported interpretations based on the stable isotope content of feathers, suggesting that the latter provided a better record of overall foraging activity than regurgitant analysis alone. Observed foraging patterns were compared to the predictions of a statistical model that determined habitat utilization based on habitat availability using a geographic information system (GIS) database. Observed foraging activities and those predicted from feathers both suggested that some adult storks preferred to feed their young freshwater prey, even when saltwater resources were more accessible in the local environment. This conclusion supports the contention that wood stork populations are sensitive to changes in the distribution of freshwater habitats along the southeastern coastal plain of the United States.

Unusual leg malformations in screech owls from a South Carolina Superfund site.

In 1995, the discovery of leg malformations in several screech owl (Otis asio) nestlings and in their female parent at a Department of Energy (DOE) Superfund site in South Carolina prompted an investigation into the nature of the observed abnormalities. Surviving nestlings and the female parent were transferred to a captive screech owl breeding colony at the USGS Patuxent Wildlife Research Center, Laurel, MD. The malformed female parent and her offspring were each mated with normal owls from the colony for 3 yr. Matings of the malfored female produced five malformed and six normal owls; all owls produced by matings of normal offspring were normal. Malformed offspring were euthanized when it became apparent that their physical distress precluded survival under normal conditions of colony care. Euthanized owls were necropsied and examined for skeletal development. Detailed descriptions of eight malformed owls are presented. Results of the matings indicated that the leg mafformations were caused by a genetic trait in the female parent that was heterozygous dominant. The characteristic was lethal except in occasional mild manifestations and resembled an extreme form of a dominant abnormality previously described for domestic fowl called duplicate polydactyly. Other reports of skeletal abnormalities in wild birds and potential environmental causes of genetic mutations at the DOE Superfund site are presented. Other studies performed at the DOE Superfund site do not implicate elevated (above background) ionizing radiation from 137Cs, the dominant radionuclide where the owls were captured, as the cause of the mutation. The cause of this genetic abnormality remains unknown.

Metals and metallothionein in the liver of raccoons: utility for environmental assessment and monitoring.

The relationship between metallothionein levels and concentrations of several metals and radionuclides was examined in liver tissues of raccoons (Procyon lotor, n = 47) from the Department of Energy's Savannah River Site in South Carolina to determine the applicability of metallothioneins as an initial screening device for exposure assessment in free-living mammals and environmental monitoring. Using a fluorescent marker and a cell sorter to measure metallothionein, a significant positive correlation was found across animals between levels of metallothioneins and concentrations of selenium (Pearson's r = .30), mercury (Pearson's r = .3 1), and copper (Pearson's r = .30) in liver tissue. Arsenic, cobalt, silver, thallium, and tin were below detection limits in most or all liver samples. Other metals, including cadmium, chromium, radiocesium (137-Cs), copper, lead, manganese, strontium, and vanadium, showed only weak and nonsignificant correlations with metallothionein. Concentrations of mercury were correlated with concentrations of selenium (Pearson's r = .73), manganese (Pearson's r = .56), and strontium (Pearson's r = .57). In an a posteriori test, there was a still unexplained positive correlation between mercury (Pearson r = .56), selenium (Pearson r = .54), and radiocesium (Pearson's r = .38) concentrations and background cellular autofluorescence, and a negative correlation of strontium with the latter (Kendall tau = -.38). Background cellular autofluorescence may represent a generalized cellular stress response, or a yet unidentified biomarker. To better understand which metals contribute to the induction of metallothionein, principle component analysis (PCA) was performed. The first three principle components explained 78% of the variance, with highest loadings being from mercury and radiocesium. Metallothionein levels did not correlate well with the principal components from the metals and radiocesium, while autofluorescent background levels tended to correlate better.

Mercury in alligators (Alligator mississippiensis) in the southeastern United States.

Mercury methylation may be enhanced in wetlands and humic-rich, blackwater systems that crocodiles and alligators typically inhabit. Given their high trophic level and long life-spans, crocodilians could accumulate significant burdens of Hg. Our objectives were to survey Hg concentrations in alligators from several areas in the southeastern United States to test their utility as sentinels of Hg contamination, to examine relationships among Hg concentrations in various tissues and to look for any differences in tissue Hg concentrations among locations. We measured total Hg concentrations in alligators collected in the Florida Everglades (n = 18), the Okefenokee National Wildlife Refuge, Georgia (n = 9), the Savannah River Site (SRS), South Carolina (n = 49) and various locations in central Florida (n = 21), sampling tissues including blood, brain, liver, kidney, muscle, bone, fat, spleen, claws and dermal scutes. Alligators from the Everglades were mostly juvenile, but Hg concentrations in tissues were high (means: liver 41.0, kidney 36.4, muscle 5.6 mg Hg/kg dry wt.). Concentrations in alligators from other locations in Florida were lower (means: liver 14.6, kidney 12.6, muscle 1.8 mg Hg/kg dry wt.), although they tended to be larger adults. Alligators from the Okefenokee were smallest and had the lowest Hg concentrations (means: liver 4.3, kidney 4.8, muscle 0.8 mg Hg/kg dry wt.). SRS alligators had the greatest size range and intermediate Hg levels (means: liver 14.9, muscle 4.8 mg Hg/kg dry wt.). At some locations, alligator length was correlated with Hg concentrations in some internal organs. However, at three of the four locations, muscle Hg was not related to length. Tissue Hg concentrations were correlated at most locations however, claw or dermal scute Hg explained less than 74% of the variation of Hg in muscle or organs, suggesting readily-obtained tissues, such as scutes or claws, have limited value for non-destructive screening of Hg in alligator populations.

Sigmoid growth and the assessment of hormesis: a case for caution.

Recent advances in procedures for the analysis of sigmoid curves have provided some sensitive methods of detecting and evaluating hormesis in the growth responses of organisms exposed to a variety of stressors. Based on a reparameterized Richards process error model, these procedures allow the quantification and independent evaluation of the three major properties of a sigmoid growth curve: size: a measure of the asymptote approached by the growth process, rate: a measure of the approximate amount of time required to complete growth, and shape: a quantity which indicates the specific path or trajectory taken by the growth process to approach the asymptote within the time constraints of the growing period. When applied to growth data for cypress tree seedlings and two species of waterfowl exposed chronically to low levels of a variety of stressors, these analyses revealed that curve shape was more likely to change in response to stress than were either asymptotic size or growth rate. The types of changes observed suggested that growth size, rate and curve shape may respond independently and in some cases, in opposite directions. Thus, while one aspect of growth may change in a fashion suggestive of hormesis (e.g. larger asymptote or faster growth rate), other aspects of the same growth function may be changing in a way suggestive of a stress response. Thus, studies designed to reveal growth hormesis should be specific with respect to which particular mathematical model is chosen, as well as with respect to which aspect of the growth response is being considered.

Clapper rails as indicators of mercury and PCB bioavailability in a Georgia saltmarsh system.

Clapper rails (Rallus longirostris) were used as an indicator species of estuarine marsh habitat quality because of their strong site fidelity and predictable diet consisting of mostly benthic organisms. Mercury (Hg) and the polychlorinated biphenyl (PCB) Aroclor 1268 concentrations were determined for sediments, crabs, as well as clapper rail adults and chicks collected from salt marshes associated with the LCP Superfund site in Brunswick, Georgia. Home ranges were established for adult rails, and sediment and crab samples were taken from each individual's range. The study was designed to minimize the spatial variability associated with trophic transfer studies by choosing an endpoint species with a potentially small home range and specifically sampling its foraging range. The mean home range for clapper rails was 1.2 ha with a median of 0.28 ha. Concentrations of Hg and Aroclor 1268 were shown to increase with each trophic level. Transfer factors between media followed the same pattern for both contaminants with the highest between fiddler crabs and clapper rail liver. Hg and PCB transfer factors were similar between sediment to fiddler crab and fiddler crab to muscle, however the PCB transfer factor from fiddler crabs to liver was over twice as large as for Hg. PCB congener profiles did not significantly differ between media types.