Biomedical subjects

J D Congdon

Publications and source records attributed to J D Congdon.

At least 19 recordsLinked to original sources

PubMed2004

Responses of benthic fish exposed to contaminants in outdoor microcosms--examining the ecological relevance of previous laboratory toxicity tests.

Previous laboratory studies indicate that coal combustion wastes (a mixture composed of fly ash and other lower volume wastes such as bottom ash; hereafter collectively referred to as ash) adversely affect the health of benthic fish (Erimyzon sucetta; lake chubsucker), but fish in these studies were provided with ample uncontaminated food resources. Because aquatic disposal of ash can also adversely affect food resources for benthic fish, we hypothesized that changes in resources might exacerbate the effects of ash on fish observed in laboratory studies. We exposed juvenile E. sucetta in outdoor microcosms to water, sediment, and benthic resources from an ash-contaminated site or a reference site for 45 days and compared our findings to previous laboratory studies. Benthic invertebrate biomass was nearly three times greater in controls compared to ash microcosms. Total organic content of control sediment (41%) was also greater than in ash sediments (17%), suggesting that additional benthic resources may have also been limited in ash microcosms. Benthic invertebrates isolated from the ash microcosms had trace element concentrations (As, Cd, Co, Cr, Cs, Se, Sr, and V) up to 18 times higher than in weathered ash used in laboratory studies. The concentrations of trace elements accumulated by fish reflected the high dietary concentrations encountered in the ash microcosms and were associated with reduced growth (final mass = 0.07 g) and survival (25%) compared to controls (0.37 g and 67%, respectively). Accumulation of trace elements, as well as reductions in growth and survival, were more pronounced than in previous laboratory studies, suggesting that resource conditions may be important in mediating ash toxicity. Taken together, our studies suggest that ash discharge into aquatic systems is a more serious threat to the health of benthic fish than previously predicted based upon laboratory toxicity tests.

Analysis of Variance↗

PubMed2004

Respiratory and reproductive characteristics of eastern mosquitofish (Gambusia holbrooki) inhabiting a coal ash settling basin.

Coal fly ash and effluent from coal ash settling basins negatively affects metabolism and reproduction in a variety of organisms, including a number of fish species. Some species, most notably the eastern mosquitofish (Gambusia holbrooki), are known to maintain viable populations in areas contaminated by coal ash. While eastern mosquitofish are present in these systems, their degree of tolerance to coal ash has not been investigated using sublethal metrics of exposure. It is possible that eastern mosquitofish persist in habitats affected by coal ash, but experience significant costs such as changes in metabolism and fecundity. Thus, we investigated the effects of coal ash on standard metabolic rate and reproduction of eastern mosquitofish inhabiting a coal-ash contaminated settling basin. Standard metabolic rates of mosquitofish from the ash contaminated site and a reference site (mean O2 consumption = 0.286 mL/g x h +/- 0.007 and 0.291 +/- 0.008 mL/g x h, respectively) were not significantly different. Despite elevated contaminant concentrations in ash basin females (selenium, arsenic, copper, and cadmium) and their offspring (selenium), brood sizes and offspring viability did not differ between clutches collected from ash basin and reference site females. Our data provide further evidence of the high degree of tolerance of eastern mosquitofish to exposure to aquatic coal ash disposal generated by power plants. However, the basis for such tolerance to ash remains unclear. Further investigations are required to determine whether such tolerance is a result of species-specific characteristics or population characteristics due to local adaptation.

Animals↗

PubMed2004

Standard and digestive metabolism in the banded water snake, Nerodia fasciata fasciata.

Estimating energy costs by respirometry is fundamental to many studies of the ecology, behavior and evolution of reptiles. However, traditional respirometry procedures seldom incorporate objective techniques for removal of outliers from estimates of metabolic parameters. We demonstrate how computer-automated respirometry equipment, which records many respiratory measurements over short intervals, can be coupled with mathematical procedures to produce robust estimates of pre- and post-prandial metabolism in banded water snakes (Nerodia fasciata fasciata). Standard metabolic rate of N. f. fasciata was estimated to be 1.21 ml O2/h (mass = 30.21 +/- 0.74 g) at 25 degrees C. After ingestion of a fish equaling 20% of their body mass, snakes exhibited a fivefold increase in metabolic rate with peak O2 consumption rate (VO2) reaching 6.5 ml O2/h. Total cost of digestion was 5.44 kJ, equivalent to approximately 21% of the energy in the meal. Repeated measurements of metabolism in the same individuals revealed that our methods yielded similar results, even when individuals exhibited different patterns of VO2 variation between respiratory trials. Our results underscore the importance of obtaining many VO2 measurements, coupled with objective removal of outlier values from estimates of metabolic rate, especially when metabolic values are to be interpreted in a comparative context.

Animals↗

PubMed2004

The influence of circadian rhythms on pre- and post-prandial metabolism in the snake Lamprophis fuliginosus.

Measuring standard metabolic rate (SMR) and specific dynamic action (SDA) has yielded insight into patterns of energy expenditure in snakes, but less emphasis has been placed on identifying metabolic variation and associated energy cost of circadian rhythms. To estimate SMR, SDA, and identify metabolic variation associated with circadian cycles in nocturnally active African house snakes (Lamprophis fuliginosus), we measured oxygen consumption rates (VO2) at frequent intervals before and during digestion of meals equaling 10%, 20% and 30% of their body mass. Circadian rhythms in metabolism were perceptible in the VO2 data during fasting and after the initial stages of digestion. We estimated SMR of L. fuliginosus (mean mass=16.7+/-0.3 g) to be 0.68+/-0.02 (+/-SEM) mL O2/h at 25 degrees C. Twenty-four hours after eating, VO2 peaked at 3.2-5.3 times SMR. During digestion of meals equaling 10-30% of their body mass, the volume of oxygen consumed ranged from 109 to 119 mL O2 for SMR, whereas extra oxygen consumed for digestion and assimilation ranged from 68 to 256 mL O2 (equivalent to 14.5-17.0% of ingested energy). The oxygen consumed due to the rise in metabolism during the active phase of the daily cycle ranged from 55 to 66 mL O2 during digestion. Peak VO2, digestive scope, and SDA increased with increasing meal size. Comparisons of our estimates to estimates derived from methods used in previous investigations resulted in wide variance of metabolic variables (up to 39%), likely due to the influence of circadian rhythms and activity on the selection of baseline metabolism. We suggest frequent VO2 measurements over multiple days, coupled with mathematical methods that reduce the influence of undesired sources of VO2 variation (e.g., activity, circadian cycles) are needed to reliably assess SMR and SDA in animals exhibiting strong circadian cycles.

Animals↗

PubMed2003

Altered swimming performance of a benthic fish (Erimyzon sucetta) exposed to contaminated sediments.

Numerous field surveys suggest that coal combustion wastes (ash) adversely affect fish populations, but few controlled laboratory studies have evaluated the responses of individual fish to ash exposure. Available information suggests that sublethal effects of ash, including decreased growth rates and reduced fecundity, may be important manifestations of ash toxicity. Here, we hypothesized that ash may also alter swimming performance, which could ultimately have important implications for the autecology of affected species. To test this hypothesis, we measured sprint speed and critical swimming speed (U(crit)) of juvenile lake chubsuckers (Erimyzon sucetta) exposed to ash in the laboratory. Fish exposed to ash for 90-100 days accumulated significant concentrations of As, Se, Sr, and V; exhibited severe fin erosion; and had reduced sprint speed and U(crit). Compared to controls, sprint speed of ash-exposed fish was reduced by 30% at 5 cm and the percent reduction was further reduced to 104% at 20 cm. Critical swimming speed was approximately 50% lower in fish exposed to ash compared to controls. Additionally, the typical positive relationship between standard length and U(crit) was absent in fish exposed to ash. Because reductions in swimming performance could not be attributed to pollutant-induced differences in body condition or fin morphology, we hypothesize that physiological disruptions (e.g., increased energy demands, decreased oxygen uptake or transport) are responsible for the observed effects and warrant further attention.

Animals↗

PubMed2003

Environmental biodosimetry: a biologically relevant tool for ecological risk assessment and biomonitoring.

Biodosimetry, the estimation of received doses by determining the frequency of radiation-induced chromosome aberrations, is widely applied in humans acutely exposed as a result of accidents or for clinical purposes, but biodosimetric techniques have not been utilized in organisms chronically exposed to radionuclides in contaminated environments. The application of biodosimetry to environmental exposure scenarios could greatly improve the accuracy, and reduce the uncertainties, of ecological risk assessments and biomonitoring studies, because no assumptions are required regarding external exposure rates and the movement of organisms into and out of contaminated areas. Furthermore, unlike residue analyses of environmental media, environmental biodosimetry provides a genetically relevant biomarker of cumulative lifetime exposure. Symmetrical chromosome translocations can impact reproductive success, and could therefore prove to be ecologically relevant as well. We describe our experience in studying aberrations in the yellow-bellied slider turtle as an example of environmental biodosimetry.

Animals↗

PubMed2002

Sperm storage in turtles: A male perspective.

The storage and behavior of sperm collected from the epididymis of two emyiid turtles were examined. In Chrysemys picta, the weight of the epididymis does not change significantly throughout the year as does the testis. However, in this species, as well as in Trachemys scripta, the epididymis contains sperm throughout the entire year. Sperm from both species have a relatively low motility and velocity of movement. In C. picta, equally low motilities are observed both in the autumn, shortly after spermiation, and in spring. Motility could be augmented by the addition of isobutyl methyl xanthine (IBMX, 0.5 mmol l(-1)). Epididymal sperm remained viable in excess of 40 days in vitro when stored in F-10 buffer, during which time motility and swimming velocity could be augmented with IBMX. The longevity and low motility of turtle sperm facilitates its storage by either males or females, and creates conditions that promote the wide dissemination, over time, of gametes produced in a narrow time window.

Adaptation, Physiological↗

PubMed2002

Effects of food ration on survival and sublethal responses of lake chubsuckers (Erimyzon sucetta) exposed to coal combustion wastes.

Study organisms in chronic toxicological bioassays are often provided with excessive resources to remove food limitations as a confounding experimental variable. Under more ecologically realistic situations, resources are often less abundant and such restrictions may alter the responses of organisms to environmental contaminants. Here, we investigated the interaction between resource level and sediment toxicity in the lake chubsucker, Erimyzon sucetta. For 78 days we fed fish one of three ration levels (1X, 2X, 4X; uncontaminated food) that was grazed directly from either clean sand or coal ash-contaminated sediments. Despite provision of uncontaminated food, fish exposed to the contaminated sediments accumulated significant whole body concentrations of As, Se, Sr, and V. Food ration affected the pattern of Se accumulation, with lowest concentrations accumulated by fish supplied with the lowest rations (1X). Paradoxically, fish in the 1X-ash treatment were most adversely effected by ash-exposure, despite having Se burdens much lower than fish in the 2X- and 4X-ash treatments. Fish in the 1X-ash treatment exhibited higher mortality, lower proportional growth, and increased incidence of fin erosion compared to fish provided with higher rations. Such results may, in part, be explained by the apparent inability of fish with reduced rations to maintain positive energy balance, as evidenced by their higher standard metabolic rates compared to control fish fed similar rations. Our results underscore the importance of considering resource quantity and nutritional factors in chronic bioassays in order to draw more ecologically realistic conclusions about contaminant effects.

Animal Feed↗

PubMed2001

Integrating individual-based indices of contaminant effects. How multiple sublethal effects may ultimately reduce amphibian recruitment from a contaminated breeding site.

Habitat contamination can alter numerous biological processes in individual organisms. Examining multiple individual-level responses in an integrative fashion is necessary to understand how individual health or fitness reflects environmental contamination. Here we provide an example of such an integrated perspective based upon recent studies of an amphibian (the bullfrog, Rana catesbeiana ) that experiences several, disparate changes when larval development occurs in a trace element-contaminated habitat. First, we present an overview of studies focused on specific responses of individuals collected from, or transplanted into, a habitat contaminated by coal combustion residues (CCR). These studies have reported morphological, behavioral, and physiological modifications to individuals chronically interacting with sediments in the CCR-contaminated site. Morphological abnormalities in the oral and tail regions in contaminant-exposed individuals influenced other properties such as grazing, growth, and swimming performance. Behavioral changes in swimming activities and responses to stimuli appear to influence predation risk in the contaminant-exposed population. Significant changes in bioenergetics in the contaminated habitat, evident as abnormally high energetic expenditures for survival (maintenance) costs, may ultimately influence production pathways (growth, energy storage) in individuals. We then present a conceptual model to examine how interactions among the affected systems (morphological, behavioral, physiological) may ultimately bring about more severe effects than would be predicted if the responses were considered in isolation. A complex interplay among simultaneously occurring biological changes emerges in which multiple, sublethal effects ultimately can translate into reductions in larval or juvenile survival, and thus reduced recruitment of juveniles into the population. In systems where individuals are exposed to low concentrations of contaminants for long periods of time, research focused on one or few sublethal responses could substantially underestimate overall effects on individuals. We suggest that investigators adopt a more integrated perspective on contaminant-induced biological changes so that studies of individual-based effects can be better integrated into analyses of mechanisms of population change.

Animals↗

PubMed2001

Accumulation and selective maternal transfer of contaminants in the turtle Trachemys scripta associated with coal ash deposition.

Coal combustion wastes are enriched in a number of potentially toxic compounds and may pose risks to biota exposed to the wastes. Slider turtles (Trachemys scripta) are common inhabitants of coal ash settling basins in South Carolina, USA, where they feed on contaminated prey items and accumulate high levels of potentially toxic compounds in their tissues. Furthermore, female sliders sometimes nest in contaminated spill piles and thus may expose embryos to contaminated soils. We examined two potential pathways by which female T. scripta may influence the survivorship and quality of their offspring in a contaminated habitat: (1) nesting in contaminated soil and (2) maternal transfer of pollutants. Eggs were collected from turtles captured in coal ash-polluted or unpolluted sites; individual clutches were incubated in both ash-contaminated and uncontaminated soil in outdoor, artificial nests. Incubation in contaminated soil was associated with reduced embryo survivorship. Adult females from the polluted site accumulated high levels of As, Cd, Cr, and Se in their tissues, yet Se was the only element transferred maternally to hatchlings at relatively high levels. Hatchlings from polluted-site females exhibited reduced O2 consumption rates compared to hatchlings from reference sites. Relatively high levels of Se transferred to hatchlings by females at the ash-polluted site might contribute to the observed differences in hatchling physiology.

Animals↗

PubMed2001

Nondestructive indices of trace element exposure in squamate reptiles.

Compared with birds, mammals, fish, and even amphibians, very little is known about the effects of contaminants on reptiles. Recent evidence that many reptile populations may be declining has stimulated demand for toxicological studies of reptiles as well as development of nondestructive sampling techniques useful for assessing and monitoring contaminant exposure. The current study experimentally evaluated the utility of shed skins, tail clips, and blood samples as nondestructive indices of trace element exposure in banded water snakes, Nerodia fasciata. For 13.5 months, snakes were either fed fish from a coal ash-contaminated site or uncontaminated food from a reference site. Snakes fed contaminated prey accumulated As, Cd, Se, Sr, and V in various organs (i.e. liver, kidney, and/or gonads). Moreover, non-parametric discriminant function analysis revealed that snakes could be placed in two groups that reliably reflected their experimental diet based upon Se, Sr, and As concentrations in tail clips, blood, and/or shed skins. We suggest that nondestructive sampling techniques, particularly analyses of blood and tail clips, may be easily applied in evaluations of contaminant exposure in the field and laboratory and may prevent excessive destructive sampling of potentially threatened reptile species.

Animals↗

PubMed2001

Hypotheses of aging in a long-lived vertebrate, Blanding's turtle (Emydoidea blandingii).

For 35 of the past 47 years, Blanding's turtles were studied on the University of Michigan's E.S. George Reserve in southeastern Michigan. Blanding's turtle is one of the longest-lived emydid turtles with individuals reaching ages greater than 75 years. We compared body sizes, reproductive traits and survival of Young, Middle, and Oldest age groups of Blanding's turtles to test predictions from two contrasting hypotheses of aging. The relative reproductive rate hypothesis predicts traits that increase the reproductive output or survival rates of older compared to younger individuals, whereas the senescence hypothesis predicts a reduction in reproductive output or survival in older versus younger individuals. Body size did not increase with age among groups; therefore, indeterminate growth was not a mechanism for increased reproductive output of the oldest individuals. Survivorship, reproductive frequency and size-adjusted mean clutch size were all higher in the Oldest age group compared to the younger age groups. Nest predation rate was highest in the Young age group compared to either group of older turtles. In nests that survived predation, the proportion of nests that failed entirely due to developmental problems was lowest in the Young, intermediate in the Middle, and highest in the Oldest age group. Successful nests produced similar numbers of hatchlings and similar sized hatchlings in all three age groups. Traits such as egg and offspring size, and offspring produced per nest did not support either the relative reproductive rate or the senescence hypothesis of aging. Increased embryo mortality in nests of older females compared to younger turtles supports predictions from the senescence hypothesis. Three traits; increased clutch size, reproductive frequency, and survivorship of individuals in the Oldest age group compared to younger turtles support the relative reproductive rate hypothesis for evolution of longevity.

Aging↗

PubMed2001

Metabolic costs incurred by crayfish (Procambarus acutus) in a trace element-polluted habitat: further evidence of similar responses among diverse taxonomic groups.

Recent studies of several vertebrates and an invertebrate have shown elevated standard metabolic rate (SMR) following chronic exposure to a mixture of trace elements in a contaminated habitat. In this study, we examined whether another invertebrate, a crayfish (Procambarus acutus), also experienced elevated SMR in response to the same contaminants. We compared SMR of individuals inhabiting the contaminated site with SMR of individuals from uncontaminated reference sites. We also examined SMR of individuals collected from the reference areas and exposed in the laboratory for 50 days to sediment and food derived from the contaminated site. Individuals collected from the contaminated site had elevated SMR compared to individuals collected from the unpolluted areas (25.1 vs. 19.2 J g(-1) day(-1)). Individuals exposed to contaminated sediment and food in the laboratory experienced elevations in SMR compared to controls after 27 days of exposure (35.2 vs. 29.4 J g(-1) day(-1)), but after 50 days of exposure, metabolic rate no longer differed between treatments. Growth of contaminant-exposed individuals was lower than growth of reference animals throughout the laboratory study. Elevated SMR associated with contaminant exposure may reflect energy-demanding mechanisms required to combat deleterious effects of contaminants. Our results support the prediction that increases in energy expenditure in the contaminated habitat would negatively influence production processes, such as growth. Results from this study in conjunction with observations from other species suggest that increased SMR is a common response among several taxa to the mixture of contaminants in the study site.

Animals↗

PubMed2001

Conservation of chromosome 1 in turtles over 66 million years.

Fluorescence in situ hybridization of a whole chromosome 1-specific probe from the yellow-bellied slider turtle (Trachemys scripta) to cells from four other species of turtle ranging from a desert tortoise to a loggerhead sea turtle resulted in specific and exclusive hybridization to chromosome 1 in all five species. Previous observations of conservation in the giemsa banding pattern and chromosome morphology and number among turtles are thus extended to the DNA sequence level, revealing a cytogenetic stability of chromosome 1 in these turtles during the past 66-144 million years. This contrasts with the situation for various hominoid species where, in many instances, extensive chromosomal rearrangements have been reported in one third of that time period. Our probe, which was prepared by microdissecting whole chromosomes from embryonic T. scripta fibroblasts and amplifying using DOP-PCR, is the first report of a whole-chromosome FISH probe for any reptile.

Animals↗

PubMed2001

Chromosome translocations in T. scripta: the dose-rate effect and in vivo lymphocyte radiation response.

Using a whole-chromosome FISH painting probe we previously developed for chromosome 1 of the yellow-bellied slider turtle (Trachemys scripta), we investigated the dose-rate effect for radiation-induced symmetrical translocations in T. scripta fibroblasts and lymphocytes. The dose rate below which no reduction in effect per unit dose is observed with further dose protraction was approximately 23 cGy h(-1). We estimated the whole-genome spontaneous background level of complete, apparently simple symmetrical translocations in T. scripta lymphocytes to be approximately 1.20 x 10(-3)/cell projected from aberrations occurring in chromosome 1. Similar spontaneous background levels reported for humans are some 6- to 25-fold higher, ranging from about 6 x 10(-3) to 3.4 x 10(-2) per cell. This relatively low background level for turtles would be a significant advantage for resolution of effects at low doses and dose rates. We also chronically irradiated turtles over a range of doses from 0-8 Gy delivered at approximately 5.5 cGy h(-1) and constructed a lymphocyte dose-response curve for complete, apparently simple symmetrical translocations suitable for use with animals chronically exposed to radiation in contaminated environments. The best-fitting calibration curve (not constrained through the zero dose estimate) was of the form Y(as) = c + aD + bD(2), where Y(as) was the number of apparently simple symmetrical translocations per cell, D was the dose (Gy), a = (0.0058 +/- 0.0009), b = (-0.00033 +/- 0.00011), and c = (0.0015 +/- 0.0013). With additional whole-chromosome probes to improve sensitivity, environmental biodosimetry using stable chromosome translocations could provide a practical and genetically relevant measurement end point for ecological risk assessments and biomonitoring programs.

Animals↗

PubMed2001

Resource allocation-based life histories: a conceptual basis for studies of ecological toxicology.

Whereas ecological assessments of contaminants are concerned with populations and higher levels of organization, most mechanistic work in toxicology is directed at effects on individuals and their parts. We propose that studies based on individuals can be useful in ecological analysis of polluted systems when based on the concepts of resource allocation-based life history analysis. At the heart of the resource allocation approach is the concept of operative environments of individuals (i.e., environmental factors influencing birth, death, or migration). Contaminants can have strong influences on operative environments, modifying resource allocation strategies that reflect changes in energy assimilation and demands. By examining contaminant-induced responses of individuals from the perspective of changing operative environments, individual-based changes and population dynamics can be addressed in an ecologically rigorous manner.

Animals↗

PubMed2000

Detrimental effects associated with trace element uptake in lake chubsuckers (Erimyzon sucetta) exposed to polluted sediments.

Lake chubsuckers (Erimyzon sucetta) were exposed to coal ash-polluted sediments under conservative experimental conditions (filtered artificial soft water and abundant uncontaminated food). After 4 months of exposure, fish grazing the polluted sediments had significantly elevated body burdens of Se, Sr, and V. Selenium levels were particularly elevated, reaching mean whole body concentrations of 5.6 microg/g dry mass by the end of experimental manipulations. Twenty-five percent of fish exposed to pollutants died during the study. All surviving fish exposed to ash exhibited substantial decreases in growth and severe fin erosion. Total nonpolar lipids were two times higher in fish from the control treatment, but percent lipid did not differ between treatments. Because fish were presented with the same amount of food during the study, it appears fish exposed to ash utilized more energy for daily activities and/or were less efficient at converting available energy to tissues for growth and storage. The results were particularly interesting because we were unable to detect differences in standard metabolic rate (SMR) of fish between treatments. Increased energy expenditures not detectable in estimates of maintenance based on SMR, such as costs of digestion or activity, may have contributed to decreased energetic efficiency. Our findings corroborate previous studies which have documented the toxicity of ash-derived pollutants in fish.

Animals↗

PubMed2000

Culture methods for turtle lymphocytes.

Optimization of culture techniques for turtle and other reptilian lymphocytes is essential for facilitating cytogenetic and immunologic research for these animals. We examined a variety of conditions and parameters relevant to turtle lymphocyte culture including: different mitogenic agents, alone and in combination; lymphocyte separation protocols; culture volume; time required to stimulate lymphocytes to mitosis; importance of humidity and gas exchange in culture incubation; suitability of different culture media; effects of varying serum concentrations; ability of interleukin-2 (IL-2) to stimulate lymphocyte growth and prevent apoptosis; and feasibility of inducing premature chromosome condensation. The best conditions of those we studied for obtaining mitotic cells were (1) the combined use of phytohemagglutinin-M form (2%) and lipopolysaccharides (0.55 microg/ml), (2) the use of 5% autologous turtle serum (as opposed to fetal bovine serum), and (3) collection of mitotic cells around 96 hours after mitogenic stimulation. Human, recombinant IL-2 did not increase the fraction of lymphocytes in mitosis over the range of concentrations tested and calyculin A was ineffective at inducing premature chromosome condensation in turtle lymphocytes over the range of concentrations tested. This test regime provides a guideline for determination of appropriate lymphocyte culture conditions in turtles and other reptiles.

Animals↗