Genetic structure in patchy populations of a candidate foundation plant: a case study of Leymus chinensis using genetic and clonal diversity

PREMISE

The distribution of genetic diversity on the landscape has critical ecological and evolutionary implications. This may be especially the case on a local scale for foundation plant species because they create and define ecological communities, contributing disproportionately to ecosystem function.

METHODS

We examined the distribution of genetic diversity and clones, which we defined first as unique multilocus genotypes (MLG), and then by grouping similar MLGs into multilocus lineages. We used 186 markers from inter-simple sequence repeats (ISSR) across 358 ramets from 13 patches of the foundation grass Leymus chinensis. We examined the relationship between genetic and clonal diversities, their variation with patch size, and the effect of the number of markers used to evaluate genetic diversity and structure in this species.

RESULTS

Every ramet had a unique MLG. Almost all patches consisted of individuals belonging to a single multilocus lineages. We confirmed this with a clustering algorithm to group related genotypes. The predominance of a single lineage within each patch could be the result of the accumulation of somatic mutations, limited dispersal, some sexual reproduction with partners mainly restricted to the same patch, or a combination of all three.

CONCLUSIONS

We found strong genetic structure among patches of L. chinensis. Consistent with previous work on the species, the clustering of similar genotypes within patches suggests that clonal reproduction combined with somatic mutation, limited dispersal, and some degree of sexual reproduction among neighbors causes individuals within a patch to be more closely related than among patches.

Inheritance of DNA methylation differences in the mangrove Rhizophora mangle

The capacity to respond to environmental challenges ultimately relies on phenotypic variation which manifests from complex interactions of genetic and nongenetic mechanisms through development. While we know something about genetic variation and structure of many species of conservation importance, we know very little about the nongenetic contributions to variation. Rhizophora mangle is a foundation species that occurs in coastal estuarine habitats throughout the neotropics where it provides critical ecosystem functions and is potentially threatened by anthropogenic environmental changes. Several studies have documented landscape-level patterns of genetic variation in this species, but we know virtually nothing about the inheritance of nongenetic variation. To assess one type of nongenetic variation, we examined the patterns of DNA sequence and DNA methylation in maternal plants and offspring from natural populations of R. mangle from the Gulf Coast of Florida. We used a reduced representation bisulfite sequencing approach (epi-genotyping by sequencing; epiGBS) to address the following questions: (a) What are the levels of genetic and epigenetic diversity in natural populations of R. mangle? (b) How are genetic and epigenetic variation structured within and among populations? (c) How faithfully is epigenetic variation inherited? We found low genetic diversity but high epigenetic diversity from natural populations of maternal plants in the field. In addition, a large portion (up to ~25%) of epigenetic differences among offspring grown in common garden was explained by maternal family. Therefore, epigenetic variation could be an important source of response to challenging environments in the genetically depauperate populations of this foundation species.

COMPONENTS OF FLOWERING TIME VARIATION IN A DESERT ANNUAL

How much of the variation seen in life histories is consistent with adaptive hypotheses, and how much requires other kinds of explanation? Differences in flowering time between Sonoran (earlier flowering) and Chihuahuan Desert (later flowering) populations of the desert annual Eriogonum abertianum Torr. (Polygonaceae) are significant, repeatable between greenhouse experiments, and persist into a second greenhouse generation. These apparent genetic differences are consistent with a hypothesis of local adaptation: field demographic studies (Fox, 1989b) show that many fewer Sonoran than Chihuahuan Desert plants survive to the summer rainy season, suggesting selection for earlier flowering in the Sonoran Desert. Within natural populations there is considerable phenological complexity: time of first flowering varies by up to six months, and individuals may have zero, one, or several reproductive episodes. Greenhouse sib analyses revealed only marginal among-family genetic variation for flowering size. The resemblance between parents and offspring for size and time of flowering varied with growth conditions, suggesting that this marginal variation among families may be at least partly due to factors other than additive genetic variance. On the other hand, moisture limitation significantly delayed the onset of flowering in two independent experiments. Variation in moisture availability in both time and space is characteristic of desert environments. The phenological complexity in natural populations may thus be generated by random variation in moisture availability, possibly in conjunction with variation in germination date and plant size. The results call into question the claim that drought generally induces flowering in desert annuals.

The Interplay Between Predation, Competition, and Nutrient Levels Influences the Survival of Escherichia coli in Aquatic Environments

Nutrient levels, competition from autochthonous microorganisms, and protozoan predation may all influence survival of fecal microorganisms as they transition from the gastrointestinal tract to aquatic habitats. Although Escherichia coli is an important indicator of waterborne pathogens, the effects of environmental stressors on its survival in aquatic environments remain poorly understood. We manipulated organic nutrient, predation, and competition levels in outdoor microcosms containing natural river water, sediments, and microbial populations to determine their relative contribution to E. coli survival. The activities of predator (protozoa) and competitor (indigenous bacteria) populations were inhibited by adding cycloheximide or kanamycin. We developed a statistical model of E. coli density over time that fits with the data under all experimental conditions. Predation and competition had significant negative effects on E. coli survival, while higher nutrient levels increased survival. Among the main effects, predation accounted for the greatest variation (40 %) compared with nutrients (25 %) or competition (15 %). The highest nutrient level mitigated the effect of predation on E. coli survival. Thus, elevated organic nutrients may disproportionately enhance the survival of E. coli, and potentially that of other enteric bacteria, in aquatic habitats.

Reservoir Sedimentation and Upstream Sediment Sources: Perspectives and Future Research Needs on Streambank and Gully Erosion

The future reliance on water supply and flood control reservoirs across the globe will continue to expand, especially under a variable climate. As the inventory of new potential dam sites is shrinking, construction of additional reservoirs is less likely compared to simultaneous flow and sediment management in existing reservoirs. One aspect of this sediment management is related to the control of upstream sediment sources. However, key research questions remain regarding upstream sediment loading rates. Highlighted in this article are research needs relative to measuring and predicting sediment transport rates and loading due to streambank and gully erosion within a watershed. For example, additional instream sediment transport and reservoir sedimentation rate measurements are needed across a range of watershed conditions, reservoir sizes, and geographical locations. More research is needed to understand the intricate linkage between upland practices and instream response. A need still exists to clarify the benefit of restoration or stabilization of a small reach within a channel system or maturing gully on total watershed sediment load. We need to better understand the intricate interactions between hydrological and erosion processes to improve prediction, location, and timing of streambank erosion and failure and gully formation. Also, improved process-based measurement and prediction techniques are needed that balance data requirements regarding cohesive soil erodibility and stability as compared to simpler topographic indices for gullies or stream classification systems. Such techniques will allow the research community to address the benefit of various conservation and/or stabilization practices at targeted locations within watersheds.

Formation of Manganese Oxide Coatings onto Sand for Adsorption of Trace Metals from Groundwater

Manganese oxide (MnO) occurs naturally in soil and has a high affinity for trace metals adsorption. In this work, we quantified the factors (pH; flow rate; use of oxidants such as bleach, HO, and O; initial Mn(II) concentrations; and two types of geologic media) affecting MnO coatings onto Ottawa and aquifer sand using batch and column experiments. The batch experiments consisted of manual and automated titration, and the column experiments mimicked natural MnO adsorption and oxidation cycles as a strategy for in situ adsorption. A Pb solution of 50 mg L was passed through MnO-coated sand at a flow rate of 4 mL min to determine its adsorption capacity. Batch experimental results showed that MnO coatings increased from pH 6 to 8, with maximum MnO coating occurring at pH 8. Regarding MnO coatings, bleach and O were highly effective compared with HO. The Ottawa sand had approximately twice the MnO coating of aquifer sand. The sequential increase in initial Mn(II) concentrations on both sands resulted in incremental buildup of MnO. The automated procedure enhanced MnO coatings by 3.5 times compared with manual batch experiments. Column results showed that MnO coatings were highly dependent on initial Mn(II) and oxidant concentrations, pH, flow rate, number of cycles (h), and the type of geologic media used. Manganese oxide coating exceeded 1700 mg kg for Ottawa sand and 130 mg kg for aquifer sand. The Pb adsorption exceeded 2200 mg kg for the Ottawa sand and 300 mg kg for the aquifer sand.

Variation among individuals in cone production in Pinus palustris (Pinaceae)

PREMISE OF THE STUDY

Reproductive output varies considerably among individuals within plant populations, and this is especially so in cone production of conifers. While this variation can have substantial effects on populations, little is known about its magnitude or causes.

METHODS

We studied variation in cone production for 2 years within a population of Pinus palustris Mill. (longleaf pine; Pinaceae). Using hurdle models, we evaluated the importance of burn treatments, tree size (dbh), canopy status (open, dominant, subordinate), and number of conspecific neighbors within 4 m (N(4)).

KEY RESULTS

Cone production of individuals-even after accounting for other variables-was strongly correlated between years. Trees in plots burned every 1, 2, or 5 years produced more cones than those burned every 7 years, or unburned. Larger trees tend to produce more cones, but the large effects of the other factors studied caused substantial scatter in the dbh-cone number relationship. Among trees in the open, dbh had little explanatory power. Subordinate trees with three neighbors produced no cones.

CONCLUSIONS

Tree size alone was a weak predictor of cone production. Interactions with neighbors play an important role in generating reproductive heterogeneity, and must be accounted for when relating cone production to size. The strong between-year correlation, together with the large variance in cone production among trees without neighbors, suggests that still more of the variance may be explainable, but requires factors outside of our study.

Demographic heterogeneity, cohort selection, and population growth

Demographic heterogeneity--variation among individuals in survival and reproduction--is ubiquitous in natural populations. Structured population models address heterogeneity due to age, size, or major developmental stages. However, other important sources of demographic heterogeneity, such as genetic variation, spatial heterogeneity in the environment, maternal effects, and differential exposure to stressors, are often not easily measured and hence are modeled as stochasticity. Recent research has elucidated the role of demographic heterogeneity in changing the magnitude of demographic stochasticity in small populations. Here we demonstrate a previously unrecognized effect: heterogeneous survival in long-lived species can increase the long-term growth rate in populations of any size. We illustrate this result using simple models in which each individual's annual survival rate is independent of age but survival may differ among individuals within a cohort. Similar models, but with nonoverlapping generations, have been extensively studied by demographers, who showed that, because the more "frail" individuals are more likely to die at a young age, the average survival rate of the cohort increases with age. Within ecology and evolution, this phenomenon of "cohort selection" is increasingly appreciated as a confounding factor in studies of senescence. We show that, when placed in a population model with overlapping generations, this heterogeneity also causes the asymptotic population growth rate lambda to increase, relative to a homogeneous population with the same mean survival rate at birth. The increase occurs because, even integrating over all the cohorts in the population, the population becomes increasingly dominated by the more robust individuals. The growth rate increases monotonically with the variance in survival rates, and the effect can be substantial, easily doubling the growth rate of slow-growing populations. Correlations between parent and offspring phenotype change the magnitude of the increase in lambda, but the increase occurs even for negative parent-offspring correlations. The effect of heterogeneity in reproductive rate on lambda is quite different: growth rate increases with reproductive heterogeneity for positive parent-offspring correlation but decreases for negative parent-offspring correlation. These effects of demographic heterogeneity on lambda have important implications for population dynamics, population viability analysis, and evolution.

The statistical mechanics of community assembly and species distribution

• Theoretically, communities at or near their equilibrium species number resist entry of new species. Such 'biotic resistance' recently has been questioned because of successful entry of alien species into diverse natural communities. • Data on 10,409 naturalizations of 5350 plant species over 16 sites dispersed globally show exponential distributions both for species over sites and for sites over number of species shared. These exponentials signal a statistical mechanics of species distribution, assuming two conditions. First, species and sites are equivalent, either identical ('neutral') or so complex that the chance a species is in the right place at the right time is vanishingly small ('idiosyncratic'); the range of species and sites in our data disallows a neutral explanation. Secondly, the total number of naturalizations is fixed in any era by a 'regulator'. • Previous correlation of species naturalization rates with net primary productivity over time suggests that the regulator is related to productivity. • We conclude that biotic resistance is a moving ceiling, with resistance controlled by productivity. The general observation that the majority of species occur naturally at only a few sites, and only a few species occur at many sites, now has a quantitative (exponential) character, offering the study of species' distributions a previously unavailable rigor.

Emergent insights from the synthesis of conceptual frameworks for biological invasions

A general understanding of biological invasions will provide insights into fundamental ecological and evolutionary problems and contribute to more efficient and effective prediction, prevention and control of invasions. We review recent papers that have proposed conceptual frameworks for invasion biology. These papers offer important advances and signal a maturation of the field, but a broad synthesis is still lacking. Conceptual frameworks for invasion do not require invocation of unique concepts, but rather should reflect the unifying principles of ecology and evolutionary biology. A conceptual framework should incorporate multicausality, include interactions between causal factors and account for lags between various stages. We emphasize the centrality of demography in invasions, and distinguish between explaining three of the most important characteristics by which we recognize invasions: rapid local population increase, monocultures or community dominance, and range expansion. As a contribution towards developing a conceptual synthesis of invasions based on these criteria, we outline a framework that explicitly incorporates consideration of the fundamental ecological and evolutionary processes involved. The development of a more inclusive and mechanistic conceptual framework for invasion should facilitate quantitative and testable evaluation of causal factors, and can potentially lead to a better understanding of the biology of invasions.

Inferring microhabitat preferences of Lilium catesbaei (Liliaceae)

PREMISE OF THE STUDY

Microhabitat studies use varied statistical methods, some treating site occupancy as a dependent and others as an independent variable. Using the rare Lilium catesbaei as an example, we show why approaches to testing hypotheses of differences between occupied and unoccupied sites can lead to erroneous conclusions about habitat preferences. Predictive approaches like logistic regression can better lead to understanding of habitat requirements.

METHODS

Using 32 lily locations and 30 random locations >2 m from a lily (complete data: 31 lily and 28 random spots), we measured physical conditions--photosynthetically active radiation (PAR), canopy cover, litter depth, distance to and height of nearest shrub, and soil moisture--and number and identity of neighboring plants. Twelve lilies were used to estimate a photosynthetic assimilation curve. Analyses used logistic regression, discriminant function analysis (DFA), (multivariate) analysis of variance, and resampled Wilcoxon tests.

KEY RESULTS

Logistic regression and DFA found identical predictors of presence (PAR, canopy cover, distance to shrub, litter), but hypothesis tests pointed to a different set (PAR, litter, canopy cover, height of nearest shrub). Lilies are mainly in high-PAR spots, often close to light saturation. By contrast, PAR in random spots was often near the lily light compensation point. Lilies were near Serenoa repens less than at random; otherwise, neighbor identity had no significant effect.

CONCLUSIONS

Predictive methods are more useful in this context than the hypothesis tests. Light availability plays a big role in lily presence, which may help to explain increases in flowering and emergence after fire and roller-chopping.

Emergent insights from the synthesis of conceptual frameworks for biological invasions

A general understanding of biological invasions will provide insights into fundamental ecological and evolutionary problems and contribute to more efficient and effective prediction, prevention and control of invasions. We review recent papers that have proposed conceptual frameworks for invasion biology. These papers offer important advances and signal a maturation of the field, but a broad synthesis is still lacking. Conceptual frameworks for invasion do not require invocation of unique concepts, but rather should reflect the unifying principles of ecology and evolutionary biology. A conceptual framework should incorporate multicausality, include interactions between causal factors and account for lags between various stages. We emphasize the centrality of demography in invasions, and distinguish between explaining three of the most important characteristics by which we recognize invasions: rapid local population increase, monocultures or community dominance, and range expansion. As a contribution towards developing a conceptual synthesis of invasions based on these criteria, we outline a framework that explicitly incorporates consideration of the fundamental ecological and evolutionary processes involved. The development of a more inclusive and mechanistic conceptual framework for invasion should facilitate quantitative and testable evaluation of causal factors, and can potentially lead to a better understanding of the biology of invasions.

Chlorpyrifos and atrazine removal from runoff by vegetated filter strips: experiments and predictive modeling

Runoff volume and flow concentration are hydrological factors that limit effectiveness of vegetated filter strips (VFS) in removing pesticides from surface runoff. Empirical equations that predict VFS pesticide effectiveness based solely on physical characteristics are insufficient on the event scale because they do not completely account for hydrological processes. This research investigated the effect of drainage area ratio (i.e., the ratio of field area to VFS area) and flow concentration (i.e., uniform versus concentrated flow) on pesticide removal efficiency of a VFS and used these data to provide further field verification of a recently proposed numerical/empirical modeling procedure for predicting removal efficiency under variable flow conditions. Runoff volumes were used to simulate drainage area ratios of 15:1 and 30:1. Flow concentration was investigated based on size of the VFS by applying artificial runoff to 10% of the plot width (i.e., concentrated flow) or the full plot width (i.e., uniform flow). Artificial runoff was metered into 4.6-m long VFS plots for 90 min after a simulated rainfall of 63 mm applied over 2 h. The artificial runoff contained sediment and was dosed with chlorpyrifos and atrazine. Pesticide removal efficiency of VFS for uniform flow conditions (59% infiltration; 88% sediment removal) was 85% for chlorpyrifos and 62% for atrazine. Flow concentration reduced removal efficiencies regardless of drainage area ratio (i.e., 16% infiltration, 31% sediment removal, 21% chlorpyrifos removal, and 12% atrazine removal). Without calibration, the predictive modeling based on the integrated VFSMOD and empirical hydrologic-based pesticide trapping efficiency equation predicted atrazine and chlorpyrifos removal efficiency under uniform and concentrated flow conditions. Consideration for hydrological processes, as opposed to statistical relationships based on buffer physical characteristics, is required to adequately predict VFS pesticide trapping efficiency.

Effectiveness of vegetative filter strips in reducing pesticide loading: quantifying pesticide trapping efficiency

Pesticide trapping efficiency of vegetated filter strips (VFS) is commonly predicted with low success using empirical equations based solely on physical characteristics such as width and slope. The objective of this research was to develop and evaluate an empirical model with a foundation of VFS hydrological, sedimentological, and chemical specific parameters. The literature was reviewed to pool data from five studies with hypothesized significant parameters: pesticide and soil properties, percent reduction in runoff volume (i.e., infiltration) and sedimentation, and filter strip width. The empirical model was constructed using a phase distribution parameter, defined as the ratio of pesticide mass in dissolved form to pesticide mass sorbed to sediment, along with the percent infiltration, percent sedimentation, and the percent clay content (R(2) = 0.86 and standard deviation of differences [STDD] of 7.8%). Filter strip width was not a statistically significant parameter in the empirical model. For low to moderately sorbing pesticides, the phase distribution factor became statistically insignificant; for highly sorbing pesticides, the phase distribution factor became the most statistically significant parameter. For independent model evaluation datasets, the empirical model based on infiltration and sediment reduction, the phase distribution factor, and the percent clay content (STDD of 14.5%) outperformed existing filter strip width equations (STDD of 38.7%). This research proposed a procedure linking a VFS hydrologic simulation model with the proposed empirical trapping efficiency equation. For datasets with sufficient information for the VFS modeling, the linked numerical and empirical models significantly (R(2) = 0.74) improved predictions of pesticide trapping over empirical equations based solely on physical VFS characteristics.

Sources of variation in growth, form, and survival in dwarf and normal-stature pitch pines (Pinus rigida, Pinaceae) in long-term transplant experiments

Determining the relative contributions of genetic and environmental factors to phenotypic variation is critical for understanding the evolutionary ecology of plant species, but few studies have examined the sources of phenotypic differentiation between nearby populations of woody plants. We conducted reciprocal transplant experiments to examine sources of variation in growth rate, form, survival, and maturation in a globally rare dwarf population of pitch pine (Pinus rigida) and in surrounding populations of normal-stature pitch pines on Long Island, New York. Transplants were monitored over a 6-yr period. The influence of seedling origin on height, growth rate, survival, and form (single-stemmed vs. multi-stemmed growth habit) was much smaller than the effect of transplanting location. Both planting site and seed origin were important factors in determining time to reproduction; seedlings originating from dwarf populations and seedlings planted at the normal-stature site reproduced earliest. These results suggest that many of the differences between dwarf and normal-stature pitch pines may be due more to plastic responses to environmental factors than to genetic differentiation among populations. Therefore, preservation of the dwarf pine habitat is essential for preserving dwarf pine communities; the dwarf pines cannot be preserved ex situ.

Consequences of heterogeneity in survival probability in a population of Florida scrub-jays

1. Using data on breeding birds from a 35-year study of Florida scrub-jays Aphelocoma coerulescens (Bosc 1795), we show that survival probabilities are structured by age, birth cohort, and maternal family, but not by sex. Using both accelerated failure time (AFT) and Cox proportional hazard models, the data are best described by models incorporating variation among birth cohorts and greater mortality hazard with increasing age. AFT models using Weibull distributions with the shape parameter > 1 were always the best-fitting models. 2. Shared frailty models allowing for family structure greatly reduce model deviance. The best-fitting models included a term for frailty shared by maternal families. 3. To ask how long a data set must be to reach qualitatively the same conclusions, we repeated the analyses for all possible truncated data sets of 2 years in length or greater. Length of the data set affects the parameter estimates, but not the qualitative conclusions. In all but three of 337 truncated data sets the best-fitting models pointed to same conclusions as the full data set. Shared frailty models appear to be quite robust. 4. The data are not adequate for testing hypotheses as to whether variation in frailty is heritable. 5. Substantial structured heterogeneity for survival exists in this population. Such structured heterogeneity has been shown to have substantial effects in reducing demographic stochasticity.

Limiting relationships between selection and recombination

It is difficult to directly observe processes like natural selection at the genetic level, but relatively easy to estimate genetic frequencies in populations. As a result, genetic frequency data are widely used to make inferences about the underlying evolutionary processes. However, multiple processes can generate the same patterns of frequency data, making such inferences weak. By studying the limits to the underlying processes, one can make inferences from frequency data by asking how strong selection (or some other process of interest) would have to be to generate the observed pattern. Here we present results of a study of the limits to the relationship between selection and recombination in two-locus, two-allele systems in which we found the limiting relationships for over 30000 sets of parameters, effectively covering the range of two-locus, two-allele problems. Our analysis relates T(min)--the minimum time for a population to evolve from the initial to the final conditions--to the strengths of selection and recombination, the amount of linkage disequilibrium, and the Nei distance between the initial and final conditions. T(min) can be large with either large disequilibrium and small Nei distance, or the reverse. The behavior of T(min) provides information about the limiting relationships between selection and recombination. Our methods allow evolutionary inferences from frequency data when deterministic processes like selection and recombination are operating; in this sense they complement methods based entirely on drift.

Variation among Individuals and Reduced Demographic Stochasticity

Population viability analysis ( PVA) is a technique that employs stochastic demographic models to predict extinction risk. All else being equal, higher variance in a demographic rate leads to a greater extinction risk. Demographic stochasticity represents variance due to differences among individuals. Current implementations of PVAs, however, assume that the expected fates of all individuals are identical. For example, demographic stochasticity in survival is modeled as a random draw from a binomial distribution. We developed a simple conceptual model showing that if there is variation among individuals in expected survival, then existing PVA models overestimate the variance due to demographic stochasticity in survival. This is a consequence of Jensen's inequality and the fact that the binomial demographic variance is a concave function of mean survival. The effect of variation among individuals on demographic stochasticity in fecundity depends on the mean-variance relationship for individual reproductive success, which is not presently known. If fecundity patterns mirror those of survival, then variation among individuals will reduce the extinction risk of small populations.

Wildlife as sentinels of human health effects in the Great Lakes--St. Lawrence basin

There is no existing formal, long-term program for gathering evidence of the incidence and severity of the health effects of toxic substances in wildlife. However, research-based studies of bald eagles, herring gulls, night herons, tree swallows, snapping turtles, mink, and beluga over the past 30 years have revealed a broad spectrum of health effects in the Great Lakes-St. Lawrence basin including thyroid and other endocrine disorders, metabolic diseases, altered immune function, reproductive impairment, developmental toxicity, genotoxicity, and cancer. These effects occurred most often and were most severe in the most contaminated sites (Green Bay, Saginaw Bay, Lake Ontario, the St. Lawrence estuary, and more recently, Lake Erie), some of which are International Joint Commission-designated Areas of Concern (AOCs). In all cases, a strong argument can be made for an environmental etiology, and in many cases for the involvement of persistent organic pollutants, particularly polychlorinated biphenyls, polychlorinated dibenzo-(italic)p(/italic)-dioxins, and polycyclic aromatic hydrocarbons. For some, the association with particular contaminants is consistent with controlled studies, and in some, dose-response relationships were documented. The biologic significance of these health impairments to the affected species is currently unclear, but they resemble those observed with increased incidence in human subpopulations in one or more AOCs. Formalizing health effects monitoring of sentinel wildlife species by the parties to the Canada-USA Great Lakes Water Quality Agreement is required. This would facilitate the optimal use of sentinel wildlife health data in a larger, epidemiologic weight-of-evidence context upon which to base decisions and policies regarding the effects of chemical exposures on human populations.

Associations between altered immune function and organochlorine contamination in young Caspian terns (Sterna caspia) from Lake Huron, 1997-1999

Previous studies of laboratory animals and wildlife species have demonstrated the immunotoxicity of organochlorines. This study confirmed that associations between organochlorines and suppressed T cell function and enhanced antibody production in young Caspian terns from the Great Lakes, first observed in the early 1990s, continued into the late 1990s. These associations were based on measurement of organochlorines in plasma of individuals and pooled egg samples. During 1997-99, immune function, hematological variables, and organochlorine contamination were measured in prefledgling Caspian terns at two Lake Huron colonies: Channel Shelter Island (Confined Disposal Facility) at the mouth of the Saginaw River in southern Saginaw Bay and Elm Island in the North Channel. Elevated organochlorine exposure, reproductive effects, and decreased recruitment have been documented previously in the Saginaw Bay colony. Concentrations of polychlorinated biphenyls (PCBs) in eggs and plasma and 1,1-dichloro-2,2-bis(p)chlorophenyl)ethylene (DDE) in plasma were consistently higher in Saginaw Bay compared to the North Channel. The mean phytohemagglutinin (PHA) skin test, a measure of T lymphocyte function, was 42% lower in Saginaw Bay. Regression analyses showed strong negative associations between the PHA response and plasma PCBs and, to a slightly lesser degree, DDE. Despite interyear differences, total antibody titers following immunization with sheep red blood cells were higher in Saginaw Bay than the North Channel. Titers were positively associated with plasma PCBs and DDE. Plasma PCBs and DDE were negatively correlated with the percentage of monocytes and positively correlated with the percentage of basophils.

Induced minisatellite germline mutations in herring gulls (Larus argentatus) living near steel mills

Despite widespread industrial release of genotoxic contaminants, little is understood of their role in inducing germline mutations in natural populations. We used multilocus DNA fingerprinting to quantify germline minisatellite mutations in families of herring gulls (Larus argentatus) in three nesting categories: (a) near cities with large steel mills operating coking ovens; (b) near cities without steel mills; and (c) in rural locations removed from point sources of contamination. Gulls nesting near integrated steel mills showed significantly higher mutation rates than gulls from rural locations (Fisher's exact, P=0.0004); urban sites without steel mills fell midway between steel and rural sites (difference from rural; Fisher's exact, P=0.19). Distance of the nesting location of herring gulls from the steel industries' coking ovens was negatively correlated with minisatellite mutation rate demonstrating significant risk for induced germline mutations in cities with steel operations (Kendall Tau; tau=0.119; P<0.0001).

Geographic variation in blood plasma protein concentrations of young herring gulls (Larus argentatus) and Caspian terns (Sterna caspia) from the Great Lakes and Lake Winnipeg

Relative and total amounts of plasma protein fractions are affected by infections, inflammation, and nutritional and physiological status, and are therefore important health indicators in free-living animals. Our objectives were: (1) to examine intercolony differences in plasma protein fractions in prefledgling gulls and terns; (2) to investigate relationships between plasma proteins and other physiological measures such as weight loss, growth, and immune function; and (3) to examine potential associations between organochlorine exposure and plasma proteins. During 1992, blood was collected from 3-week-old herring gull (Larus argentatus) chicks from six sites on Lakes Superior, Huron, Michigan, Erie, and Winnipeg and from 3-week-old Caspian tern (Sterna caspia) chicks from five sites on Lakes Huron, Michigan, and Ontario. These sites provided a wide gradient of organochlorine contamination. Plasma proteins were separated by high-resolution agarose gel electrophoresis and stained with Coomassie brilliant blue dye. Six major fractions were quantified: prealbumin, albumin, alpha-globulins, beta(1)-globulins, beta(2)-globulins, and gamma-globulins. Total protein, prealbumin, albumin, and gamma-globulin concentrations and the albumin/globulin ratio did not differ among sites. Total protein, albumin, and the albumin/globulin ratio were not decreased in birds experiencing food stress or weight loss. Intersite differences were found in alpha- and beta-globulins. In gulls, beta(2)-globulins were positively associated with polychlorinated biphenyls (PCBs) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ether (DDE). In terns, PCBs were negatively associated with alpha-globulins and positively associated with beta(1)-globulins. Additional research is needed to identify individual proteins and elucidate causal relationships between the particular protein concentrations and factors such as contaminants, growth, and condition.

Geographic variation in hematological variables in adult and prefledgling herring gulls (Larus argentatus) and possible associations with organochlorine exposure

The objectives of this study were (1) to describe variation in hematological values found in adult and prefledgling herring gulls (Larus argentatus) over a large geographic area, (2) to investigate relationships between hematological variables and other physiological indices, and (3) to examine potential associations between exposure to organochlorines and hematological variables. During 1991-93, we sampled 160 breeding adult gulls from 13 colonies and 101 4-week-old gulls from 11 colonies. All colonies were in the Great Lakes ecosystem, except for two colonies on Lake Winnipeg and the Atlantic coast. The hematological values measured in this study were similar to published values for herring gulls and related species. Significant intersite differences were found in hematological variables. Sex had little or no influence on leukocyte variables. Adults had lower total leukocyte counts and higher heterophil to lymphocyte ratios than chicks. PCV was lower in adult females than males. In adults, total leukocyte and total heterophil numbers were negatively associated with liver activity of ethoxyresorufin-O-deethylase (EROD) and concentrations of highly carboxylated porphyrins (HCPs), two biomarkers of organochlorine exposure. Total leukocyte and total heterophil numbers were positively associated with liver concentrations of DDE (1, 1-dichloro-2,2-bis(p-chlorophenyl)ethylene), and total lymphocytes were associated positively with PCB (polychlorinated biphenyl) and HCP concentrations. The heterophil to lymphocyte ratio was negatively associated with liver EROD activity and HCPs. In chicks, there was a positive association between the heterophil to lymphocyte ratio and HG-TEQs (dioxin toxicity equivalents calculated using herring gull-specific equivalency factors). PCV was associated with some measures of contaminant exposure in adults and chicks. Additional research is needed to elucidate causal relationships between hematological indices and such factors as contaminants, disease, and nutrition.

Dissociable cognitive impairments in problem drinkers

Patients in a treatment programme for severe alcohol dependence were tested on a battery of tests designed to examine organizational and visuo-spatial abilities. Analysis using a case-study approach indicated independent organizational and visuo-spatial impairments. An understanding of aetiological factors underlying these cognitive deficits and implications for treatment are discussed.

Spatial structure, environmental heterogeneity, and population dynamics: analysis of the coupled logistic map

Spatial extent can have two important consequences for population dynamics: It can generate spatial structure, in which individuals interact more intensely with neighbors than with more distant conspecifics, and it allows for environmental heterogeneity, in which habitat quality varies spatially. Studies of these features are difficult to interpret because the models are complex and sometimes idiosyncratic. Here we analyze one of the simplest possible spatial population models, to understand the mathematical basis for the observed patterns: two patches coupled by dispersal, with dynamics in each patch governed by the logistic map. With suitable choices of parameters, this model can represent spatial structure, environmental heterogeneity, or both in combination. We synthesize previous work and new analyses on this model, with two goals: to provide a comprehensive baseline to aid our understanding of more complex spatial models, and to generate predictions about the effects of spatial structure and environmental heterogeneity on population dynamics. Spatial structure alone can generate positive, negative, or zero spatial correlations between patches when dispersal rates are high, medium, or low relative to the complexity of the local dynamics. It can also lead to quasiperiodicity and hyperchaos, which are not present in the nonspatial model. With density-independent dispersal, spatial structure cannot destabilize equilibria or periodic orbits that would be stable in the absence of space. When densities in the two patches are uncorrelated, the probability that the population in a patch reaches extreme low densities is reduced relative to the same patch in isolation; this "rescue effect" would reduce the probability of metapopulation extinction beyond the simple effect of spreading of risk. Pure environmental heterogeneity always produces positive spatial correlations. The dynamics of the entire population is approximated by a nonspatial model with mean patch characteristics. This approximation worsens as the difference between the patches increases and the dispersal rate decreases: Under extreme conditions, destabilization of equilibria and periodic orbits occurs at mean parameter values lower than those predicted by the mean parameters. Apparent within-patch dynamics are distorted: The local population appears to have the wrong growth parameter and a constant number of immigrants (or emigrants) per generation. Adding environmental heterogeneity to spatial structure increases the occurrence of spatially correlated population dynamics, but the resulting temporal dynamics are more complex than would be predicted by the mean parameter values. The three classes of spatial pattern (positive, negative, and zero correlation), while still mathematically distinct, become increasingly similar phenomenologically.

Coronary artery bypass graft surgery in Newfoundland and Labrador

BACKGROUND

Newfoundland and Labrador, like other health care jurisdictions, is faced with widening gaps between the demands for health care and a strained ability to supply the necessary resources. The authors carried out a study to determine the rates of appropriate and inappropriate coronary artery bypass grafting (CABG) in the province and the waiting times for this surgery.

METHODS

This retrospective cohort study was performed in the tertiary care hospital that receives all referrals for coronary angiography and coronary artery revascularization for Newfoundland and Labrador. By reviewing the hospital records, the authors identified 2 groups of patients: those in whom critical coronary artery disease was diagnosed on the basis of coronary angiography and who were referred for CABG between Apr. 1, 1994, and Mar. 31, 1995, and those who actually underwent the procedure during that period. By applying specific criteria developed by the RAND Corporation, the authors determined the appropriateness and necessity of CABG in each case. They also compared waiting times for CABG with optimal waiting times; as determined by a consensus-based priority score.

RESULTS

A total of 338 patients underwent CABG during the study period. The cases were characterized by multivessel disease and late-stage angina symptoms. Almost all of the patients had high appropriateness scores (7-9), and nearly 95% had high necessity scores (7-9). However, during the study period, the waiting list increased by about 20%, because a total of 391 patients were referred by the weekly cardiovascular surgery conference; the authors identified these and an additional 31 patients as having necessity scores of 7 or more. Only 7 (23%) of 31 patients for whom CABG was considered very urgent underwent surgery within the recommended 24 hours, and only 30 (24%) of the 122 patients for whom CABG was considered urgent underwent surgery within the recommended 72 hours.

INTERPRETATION

These results provide evidence that the cardiac surgery program in Newfoundland and Labrador is performing CABG in patients for whom surgical revascularization is highly appropriate and necessary. Access to CABG is less than ideal, however, since the waiting list continues to expand, and many patients wait beyond the recommended time for surgery.

Organochlorine-associated immunosuppression in prefledgling Caspian terns and herring gulls from the Great Lakes: an ecoepidemiological study

The objectives of study were to determine whether contaminant-associated immunosuppression occurs in prefledgling herring gulls and Caspian terns from the Great Lakes and to evaluate immunological biomarkers for monitoring health effects in wild birds. During 1992 to 1994, immunological responses and related variables were measured in prefledgling chicks at colonies distributed across a broad gradient of organochlorine contamination (primarily polychlorinated biphenyls), which was measured in eggs. The phytohemagglutinin skin test was used to assess T-lymphocyte function. In both species, there was a strong exposure-response relationship between organochlorines and suppressed T-cell-mediated immunity. Suppression was most severe (30-45%) in colonies in Lake Ontario (1992) and Saginaw Bay (1992-1994) for both species and in western Lake Erie (1992) for herring gulls. Both species exhibited biologically significant differences among sites in anti-sheep red blood cells antibody titers, but consistent exposure-response relationships with organochlorines were not observed. In Caspian terns and, to a lesser degree, in herring gulls, there was an exposure-response relationship between organochlorines and reduced plasma retinol (vitamin A). In 1992, altered White blood cell numbers were associated with elevated organochlorine concentrations in Caspian terns but not herring gulls. The immunological and hematological biomarkers used in this study revealed contaminant-associated health effects in wild birds. An epidemiological analysis strongly supported the hypothesis that suppression of T-cell-mediated immunity was associated with high perinatal exposure to persistent organochlorine contaminants.

Circulatory sequelae of administering CPAP in hyperdynamic sepsis are time dependent

Evidence questions the circulation's ability to acutely compensate for abrupt changes in O2 delivery (Qo2). Because both sepsis and continuous positive airway pressure (CPAP) may alter the metabolic regulation of tissue oxygenation, we designed an experiment to determine the interaction, if any, between sepsis and time on circulatory homeostasis after the application of CPAP. Twenty-four sheep were randomized to cecal ligation and perforation (CLP) or sham procedure (Sham) and then rerandomized to receive either CPAP (10 mmHg) or no CPAP (No CPAP; CLP/CPAP, n = 8; CLP/No CPAP, n = 8; Sham/CPAP, n = 4; Sham/No CPAP, n = 4). Forty-eight hours later, CLP animals demonstrated an elevated cardiac index (+63%), systemic Qo2 (+49%), and systemic O2 uptake (+28%). Organ blood flow, measured with radiolabeled microspheres, was augmented to the heart and depressed in organs comprising the splanchnic circulation. Compared with the CLP/No CPAP group and both Sham groups, myocardial Qo2 in the CLP/ CPAP group was significantly elevated when measured both 2 and 8 h after CPAP. These changes were unrelated to differences in mean heart work between the study groups. Simultaneously, QO2 to all of the small gut, large gut, pancreas, and kidney in the CLP/CPAP group was elevated during the 2-h study yet reverted to levels not different from baseline by the 8-h study. These data demonstrate 1) a unique sepsis x time interaction with the use of 10 mmHg of CPAP, particularly in the "nonvital" circulations, and 2) CPAP effects on the septic coronary circulation, which were unexplained by changes in external determinants of myocardial O2 need.

Cyclooxygenase inhibition and vascular reactivity in a rat model of hyperdynamic sepsis

We postulated that the attenuated pulmonary and systemic vascular contractility observed in sepsis was secondary to the release of vasodilator prostaglandins. We used the cyclooxygenase inhibitor meclofenamate to inhibit prostaglandin synthesis in an unanesthetized, chronically instrumented model of hyperdynamic sepsis. Sixteen male Sprague-Dawley rats (300-350 g) were randomized to either sepsis induced by cecal ligation and perforation (CLP, n = 8) or a sham procedure (Sham, n = 8). Vascular reactivity was assessed by measuring the hypoxic (FiO2 = 0.08) pulmonary pressor response (HPV), and the systemic pressor response to an intravenous infusion of phenylephrine (1.5-7.5 micrograms/kg/min) before and after the administration of meclofenamate (5 mg/kg intravenously, i.v.). Twenty-four hours postoperatively, CLP animals had significantly increased cardiac output (CO) as compared with Sham animals (204 +/- 12 vs. 148 +/- 5 ml/min, p < 0.05), slightly decreased mean arterial pressure (MAP) (109 +/- 4 vs. 118 +/- 3 mm Hg, p < 0.05), and decreased total systemic vascular resistance (TSVR) (0.546 +/- 0.046 vs. 0.805 +/- 0.030 mm Hg.min.ml-1, p < 0.05). Mean pulmonary artery pressure (MPAP) and total pulmonary vascular resistance (TPVR) were similar in both groups (p > 0.05). In response to hypoxia, the change in MPAP (delta MPAP) was 3.6 +/- 1.0 and 6.9 +/- 0.8 (mm Hg) in CLP and Sham animals, respectively (p < 0.05). Similarly, the change in TPVR (delta TPVR) during hypoxia was 0.012 +/- 0.006 and 0.038 +/- 0.009 mm Hg.min.ml-1 in CLP and Sham (p < 0.05). The pulmonary and systemic blood pressure (BP) response to phenylephrine was also attenuated in CLP as compared with Sham animals. After treatment with meclofenamate, differences were no longer apparent in the HPV response between CLP and Sham animals, due to a slight increase in the HPV response of CLP animals and a slight decrease in the HPV response in Sham animals. The attenuated pressor response to phenylephrine was not changed in either the pulmonary or the systemic circulation after the administration of meclofenamate. These data suggest that vasodilator prostaglandins may contribute to the attenuated pulmonary pressor response in sepsis. However, the mechanism of the attenuated HPV may be different than the attenuated response to exogenous catecholamines since meclofenamate had no effect on either the pulmonary or systemic response to a phenylephrine infusion in septic animals.

Calcitonin gene-related peptide does not mediate the abnormal vascular reactivity observed in a rat model of acute Pseudomonas pneumonia

Abnormal systemic and pulmonary vascular reactivity has been demonstrated in numerous models of sepsis and pneumonia. Furthermore, the attenuated hypoxic pulmonary pressor response observed in these animals probably is responsible for the ventilation/perfusion (V/Q) mismatching and consequent arterial hypoxemia. We hypothesized that excess release of endogenous vasodilators such as calcitonin gene-related peptide (CGRP) in pneumonia was responsible for the diminished hypoxic pressor response. Using the CGRP receptor antagonist CGRP (8-37), we examined the role of CGRP in the attenuated hypoxic pulmonary response in a rat model of acute Pseudomonas pneumonia. Sixteen Sprague-Dawley rats were instrumented for chronic hemodynamic monitoring and subsequently randomized to either Pneumonia (n = 8), induced by the instillation of 0.2 ml broth containing 2 x 10(8) colony-forming units (CFU)/ml Pseudomonas aeruginosa into the right lower lobe, or Sham (n = 8) procedure. Hemodynamic measurements and the hypoxic (FiO2 = 0.08) pulmonary pressor response were recorded at baseline, 48 h after the pneumonia or sham procedure and after the administration of 250 micrograms CGRP (8-37) (post-CGRP(8-37)). The regional distribution of pulmonary blood flow was determined by the injection of radioactive microspheres. Forty-eight hours after the instillation of Pseudomonas, Pneumonia animals had significantly increased cardiac output (CO) as compared with Sham (193 +/- 7 vs. 154 +/- 7 ml/min, p < 0.05), slightly decreased mean arterial pressure (MAP 109 +/- 4 vs. 118 +/- 3 mm Hg, p = NS), and reduced total systemic vascular resistance (TSVR 0.57 +/- 0.03 vs. 0.78 +/- 0.05 mm Hg.min.ml-1, p < 0.05). Pneumonia animals were further characterized by increased mean pulmonary artery pressure (MPAP) as compared with Sham (24 +/- 2 vs. 20 +/- 1 mm Hg, p < 0.05) animals, and an increased alveolar-arterial (A-a) oxygen gradient (31 +/- 3 vs. 20 +/- 4 mm Hg, p < 0.05). The administration of CGRP (8-37) did not alter baseline hemodynamic variables and did not change the pressor response to hypoxia in either group. Furthermore, CGRP receptor blockade did not alter the distribution of blood flow in the lung during normoxia or hypoxia. These data suggest that although this model of acute pneumonia is characterized by an attenuated hypoxic pressor response, the mechanism does not appear to be mediated by excess release of the vasodilator CGRP.

Tinkering with the tinkerer: pollution versus evolution

Pollutants can act as powerful selective forces by altering genetic variability, its intergenerational transfer, and the size, functional viability, adaptability, and survival of future generations. It is at the level of the cell and the individual that meiosis occurs, that genetic diversity is maintained, and behavior, reproduction, growth, and survival occur and are regulated. It is at this level that evolutionary processes occur and most pollutants exert their toxic effects. Chronic exposure to chemicals contributes to the cumulative stress on individuals and disrupts physiological processes and chemically mediated communication thereby threatening the diversity and long-term survival of sexually reproducing biota. Regional or global effects of pollution on the atmosphere, hydrosphere, and lithosphere have indirectly altered Earth's life-support systems, thereby modifying trace metal balance, reproduction, and incidence of UV-B-induced DNA damage in biota. By altering the competitive ability and survival of species, chemical pollutants potentially threaten evolutionary processes and the biodiversity and function of intercepting ecosystems.

Effect of inhibition of NO synthase on vascular reactivity in a rat model of hyperdynamic sepsis

To evaluate the role of nitric oxide (NO) in the attenuated vascular reactivity observed in sepsis, we utilized the specific NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME). Male Sprague-Dawley rats (n = 16) were randomized to either sepsis induced by cecal ligation and perforation (CLP; n = 8) or sham procedure (Sham; n = 8). Vascular reactivity was assessed by measuring the pulmonary pressor response to hypoxia (HPV) (fractional inspired O2 concentration = 0.08) and the pulmonary and systemic pressor response to an intravenous infusion of phenylephrine (1.5-6.0 micrograms.kg-1.min-1). Twenty-four hours after surgery, CLP animals had significantly attenuated HPV compared with Sham animals. In response to hypoxia the change in total pulmonary vascular resistance during hypoxia was 0.008 +/- 0.004 and 0.021 +/- 0.006 mmHg.min-ml-1 in CLP and Sham animals, respectively (P < 0.05). The pulmonary and systemic blood pressure response to phenylephrine was also attenuated in CLP compared with Sham animals. After L-NAME infusion (15 mg/kg), there was a significant augmentation of the HPV response in Sham animals. In contrast, the HPV response in CLP animals was unchanged after L-NAME. The attenuated pressor response to phenylephrine in neither the pulmonary nor the systemic circulation was changed after the administration of L-NAME. These data suggest that in rats, excess NO is not an important mediator of the attenuated vascular reactivity observed in sepsis.

Hematocrit modifies the circulatory control of systemic and myocardial oxygen utilization in septic sheep

OBJECTIVE

To describe the relationship between hematocrit and oxygen utilization before and after the onset of a hyperdynamic septic state.

DESIGN

Prospective, observational study.

SETTING

Laboratory of a large university-affiliated medical school.

SUBJECTS

Thirty mature sheep, each weighing 30 to 40 kg (0.9 to 1.1 m2 body surface area).

INTERVENTIONS

After baseline measurements, cecal ligation and perforation were used to establish an intra-abdominal source of infection. The abdominal wound was closed and animals were studied on the second postoperative day. An increase in cardiac output of > or = 30% was used to arbitrarily define the onset of sepsis. Repeat measurements were performed and the animal was killed.

RESULTS

The circulatory response to this septic insult included an increase in both cardiac index (change, baseline to sepsis, delta +2.24 +/- 0.75 L/min/m2; p < .01) and myocardial blood flows (delta +76.4 +/- 56 mL/100 g/min; p < .01). We found a negative correlation between the hematocrit and cardiac index (r2 = .21; p < .01) during the septic study, and noted that the amount (p < .01) of this correlation was significantly greater in the septic than the nonseptic study. Concurrently, the negative correlation observed between hematocrit and whole-body oxygen extraction (r2 = .21; p < .01) was significantly lower (p < .01) across the range of hematocrit values examined during the septic study vs. the similar relationship in the nonseptic study (r2 = .27; p < .01). The increase in myocardial oxygen consumption paralleled the relationship between cardiac work and hematocrit in the septic study, and was accompanied by increases in both myocardial blood flows (r2 = .25; p < .01) and myocardial oxygen extraction (r2 = .35; p < .01).

CONCLUSIONS

The normal circulatory compensation to anemia in hyperdynamic sepsis includes increases in cardiac index and whole-body oxygen extraction, although greater reliance is likely placed on the use of systemic flow reserve to maintain tissue oxygen uptake in septic vs. healthy study conditions. Furthermore, increased reliance on myocardial oxygen extraction in sepsis suggests that the normal flow-reserve supporting myocardial oxygen availability may be limited in this syndrome.

Accuracy of portable chest radiography in the critical care setting. Diagnosis of pneumonia based on quantitative cultures obtained from protected brush catheter

Sixty-six supine portable chest radiographs done on the day of bronchoscopy in 62 critical care unit patients suspected of having pneumonia were examined in a blinded fashion by two radiologists. Quantitative culture results obtained from protected brush catheter (PBC) specimens were compared with chest radiograph scores. For one observer, the sensitivity of the chest radiograph for predicting the presence of positive culture results was 0.60, specificity was 0.29, overall agreement was 0.41, positive predictive value was 0.34, and negative predictive value was 0.55. For the second observer, the values were as follows: sensitivity, 0.64; specificity, 0.27; overall agreement, 0.41; positive predictive value, 0.35; and negative predictive value, 0.55. The kappa statistic was calculated at 0.27 indicating marginal interobserver reproducibility. We conclude the portable chest radiograph in the critical care setting is not accurate in predicting the presence of pneumonia when the diagnosis is based on quantitative cultures obtained from protected brush catheter specimens.

Newcastle disease in wild water birds in western Canada, 1990

This report describes the investigation of mortality of double-crested cormorants (Phalacrocorax auritus), white pelicans (Pelecanus erythrorhynchos), and gulls (Larus spp.) in Alberta, Saskatchewan, and Manitoba during late summer 1990. Techniques used varied among areas, but virological and histopathological examination of birds was done in each area. The major clinical sign in cormorants was inability to fly, often with unilateral wing or leg paralysis. Focal nonsuppurative inflammation was present in the brain and spinal cord of cormorants and pelicans. Newcastle disease virus (NDV) was isolated from cormorants, a pelican, and a ring-billed gull (Larus delawarensls) from Saskatchewan. Cormorants from Alberta were positive for NDV in an immunofluorescent test. Most of the viruses were classed as velogenic and all had a similar monoclonal antibody profile to viruses from the 1970 to 1974 panzootic. Approximately half of cormorant, pelican, and gull eggs collected from affected colonies in the spring of 1991 had antibody to NDV. Antibody was also present in cormorant eggs from the Great Lakes. No unusual mortality was detected at any colony in 1991. Fledgling cormorants and gulls from colonies where mortality occurred in 1990 did not have antibody to NDV in June-July 1991. The overall extent of mortality among water birds and the source of the virus were not determined.