Michael W. Meyer

Effects of Environmental Methylmercury on the Health of Wild Birds, Mammals, and Fish

Abstract Wild piscivorous fish, mammals, and birds may be at risk for elevated dietary methylmercury intake and toxicity. In controlled feeding studies, the consumption of diets that contained Hg (as methylmercury) at environmentally realistic concentrations resulted in a range of toxic effects in fish, birds, and mammals, including behavioral, neurochemical, hormonal, and reproductive changes. Limited field-based studies, especially with certain wild piscivorous bird species, e.g., the common loon, corroborated laboratory-based results, demonstrating significant relations between methylmercury exposure and various indicators of methylmercury toxicity, including reproductive impairment. Potential population effects in fish and wildlife resulting from dietary methylmercury exposure are expected to vary as a function of species life history, as well as regional differences in fish-Hg concentrations, which, in turn, are influenced by differences in Hg deposition and environmental methylation rates. However, population modeling suggests that reductions in Hg emissions could have substantial benefits for some common loon populations that are currently experiencing elevated methylmercury exposure. Predicted benefits would be mediated primarily through improved hatching success and development of hatchlings to maturity as Hg concentrations in prey fish decline. Other piscivorous species may also benefit from decreased Hg exposure but have not been as extensively studied as the common loon.

Winter chemical defense of Alaskan balsam poplar against snowshoe hares.

Palatabilities of parts and growth stages of balsam poplar (Populus balsamifera) to snowshoe hares (Lepus americanus) are related to concentrations of specific plant metabolites that act as antifeedants. Buds are defended from hares by cineol, benzyl alcohol, and (+)-α-bisabolol. Internodes are defended by 6-hydroxycylohexenone (6-HCH) and salicaldehyde. Although defense of interaodes depends upon both compounds, the defense of juvenile internodes is principally related to salicaldehyde concentration; the defense of internode current annual growth is principally related to 6-HCH concentration. The concentration of 6-HCH can be supplemented by the hydrolysis of phenol glycosides when plant tissue is disrupted, raising the possibility of a dynamic element of the chemical defense of poplar.

The oral bioavailability and toxicokinetics of methylmercury in common loon ( Gavia immer ) chicks

We compared the toxicokinetics of methylmercury in captive common loon chicks during two time intervals to assess the impact of feather growth on the kinetics of mercury. We also determined the oral bioavailability of methylmercury during these trials to test for age-related changes. The blood concentration-time curves for individuals dosed during feather development (initiated 35 days post hatch) were best described by a one-compartment toxicokinetic model with an elimination half-life of 3 days. The data for birds dosed following completion of feather growth (84 days post hatch) were best fitted by a two-compartment elimination model that includes an initial rapid distribution phase with a half-life of 0.9 days, followed by a slow elimination phase with a half-life of 116 days. We determined the oral bioavailability of methylmercury during the first dosing interval by comparing the ratios of the area under the blood concentration-time curves (AUC(0--> infinity )) for orally and intravenously dosed chicks. The oral bioavailability of methylmercury during the first dosing period was 0.83. We also determined bioavailability during both dosing periods using a second measure because of irregularities with intravenous results in the second period. This second bioavailability measure estimated the percentage of the dose that was deposited in the blood volume (f), and the results show that there was no difference in bioavailability among dosing periods. The results of this study highlight the importance of feather growth on the toxicokinetics of methylmercury.

Impact of lakeshore development on green frog abundance

Many amphibian species exhibit metapopulation spatial dynamics and temporally are faced with local population extinction and re-colonization. These natural population fluctuations can exhibit stochastic effects when human-caused alteration and fragmentation of habitats occur during sensitive life-cycle events. In this study, we explored the effects of shoreline development on adult green frogs Rana clamitans melanota on lakes (n=24) of northern Wisconsin. We estimated green frog abundance using both auditory and direct observation surveys. The immediate shoreline habitat was mapped and placed into a Geographical Information System (GIS) for analysis. Adult green frog populations were significantly lower on lakes with varying degrees of shoreline house and cottage development than lakes with little or no development. A negative linear relationship existed between shoreline development densities and the number of adult green frogs. However, house and cottage densities alone did not directly explain this reduction. Analysis of variance (ANOVA) identified that the amount of suitable habitat, not development density, significantly affected green frog abundance. Therefore, greater development densities significantly decrease breeding habitat quality, resulting in lower adult frog abundance. These and other findings suggest that lakeshore development regulations are not protecting sensitive amphibian species. # 2002 Elsevier Science Ltd. All rights reserved.

Effects of methylmercury exposure on the immune function of juvenile common loons (Gavia immer)

We conducted a dose-response laboratory study to quantify the level of exposure to dietary Hg, delivered as methylmercury chloride (CH3HgCl), that is associated with suppressed immune function in captive-reared common loon (Gavia immer) chicks. We used the phytohemagglutinin (PHA) skin test to assess T-lymphocyte function and the sheep red blood cell (SRBC) hemagglutination test to measure antibody-mediated immunity. The PHA stimulation index among chicks receiving dietary Hg treatment did not differ significantly from those of chicks on the control diet (p = 0.15). Total antibody (immunoglobulin [Ig] M [primary antibody] + IgG [secondary response]) production to the SRBC antigen in chicks treated with dietary methylmercury (MeHg), however, was suppressed (p = 0.04) relative to chicks on control diets. Analysis indicated suppression of total Ig production (p = 0.025 with comparisonwise alpha level = 0.017) between control and 0.4 microg Hg/g wet food intake treatment groups. Furthermore, the control group exhibited a higher degree of variability in antibody response compared to the Hg groups, suggesting that in addition to reducing the mean response, Hg treatment reduced the normal variation attributable to other biological factors. We observed bursal lymphoid depletion in chicks receiving the 1.2 microg Hg/g treatment (p = 0.017) and a marginally significant effect (p = 0.025) in chicks receiving the 0.4 microg Hg/g diet. These findings suggest that common loon chick immune systems may be compromised at an ecologically relevant dietary exposure concentration (0.4 microg Hg/g wet wt food intake). We also found that chicks hatched from eggs collected from low-pH lakes exhibited higher levels of lymphoid depletion in bursa tissue relative to chicks hatched from eggs collected from neutral-pH lakes.

Antiherbivore Chemistry of Larrea Tridentata: Effects on Woodrat (Neotoma Lepida) Feeding and Nutrition

During winter, creosote bush (Larrea tridentata) dominates the diet of desert woodrats (Neotoma lepida) in the California Mojave Desert. The stems and leaves of creosote foliage are coated with large quantities of phenolic resins (10-25% of dry mass). We investigated whether woodrats feeding on creosote were influenced behaviorally by the resin and whether ingestion of creosote resin reduced the digestibility of protein as hy- pothesized by Rhoades and Cates (1976). Preference trials demonstrated that woodrats consistently selected creosote plant parts of low resin content. Removal of the resin with diethyl ether ameliorated this feeding preference and increased overall palatability of creosote foliage. Addition of the resin to laboratory chow ration caused this food to be avoided also. When woodrats were fed rations of creosote foliage or resin-treated laboratory chow no reduction in protein digestibility occurred. However, dry matter intake was reduced when woodrats were fed chow containing 12% resin. Our results indicate that creosote resin does deter feeding by desert woodrats. The antiherbivore mechanism of creosote resin to desert woodrats is likely one of toxicity and not digestibility reduction. This toxicity may limit the amount of creosote foliage woodrats can consume, which would explain the winter body mass decline and mortality that we observed in woodrats on our study site. We discuss the impact plant defense chemistry may have had on the evolution of Neotoma in the southwestern deserts of North America.

Influence of lakeshore development on breeding bird communities in a mixed northern forest

We report findings of a 2-year study (1996–1997) surveying breeding birds in lacustrine habitats of northern Wisconsin, USA. This area has seen marked increases in lakeshore housing development in recent years, and other studies indicate significant lakeshore habitat alteration. We paired developed and undeveloped lakes of similar physical characteristics and performed point-counts around the perimeter of each to assess bird community structure. Our results showed no significant differences between developed and undeveloped lakes in bird abundance, richness or species diversity. However, several species and some resource-guilds were commonly associated with one lake-type or the other. We found a significantly higher diversity of diet guilds on developed lakes. Significant declines in the prevalence of insectivorous and ground-nesting birds were documented on developed lakes, contrasting with increased prevalence of seed-eating birds and deciduous-tree nesting birds. Levels of development on lakeshores in northern Wisconsin appear to affect the composition of avian communities, which is of concern for the health of these forested lacustrine habitats. We outline several factors associated with development which may be linked to these observed bird community changes and suggest measures landowners might take to minimize impact on native breeding bird communities. # 2002 Published by Elsevier Science Ltd.

COMPARISONS OF UNDEVELOPED AND DEVELOPED SHORELANDS, NORTHERN WISCONSIN, AND RECOMMENDATIONS FOR RESTORATION

Development of lakeshores has occurred at unprecedented levels in recent decades. Changes in the shoreland ecosystem concomitant with this development have been little studied. In this study, we compared the structural and floristic characteristics of vegetation at 97 developed and 85 undeveloped (reference) shoreland sites in northern Wisconsin, USA. Quantitative comparisons of vegetation structural characteristics (percent cover of canopy, subcanopy, and understory vegetation layers; percent of shoreline overhung by trees and shrubs; and amount of coarse woody debris) showed significantly greater complexity and cover at undeveloped versus developed sites. We classified plant communities and described plant species composition along three belt transects parallel to shore (upland, shoreline, and shallow water) using ordination techniques to describe the differences between developed and undeveloped sites, as well as among undeveloped sites. The mean number of plant species and the percent of native species were both greater at undeveloped than at developed sites along all three transects. Undeveloped upland sites could be grouped by plant species composition into three types: Northern Wet Forest (bog species), Northern Mesic Forest, and Northern Xeric Forest. Undeveloped shoreline vegetation was also clustered into three categories: bog species, upland species with an abrupt transition to aquatic species, and wet meadow species. Soil characteristics further distinguished the upland and shoreline categories. No distinct vegetation categories emerged in the shallow water ordination. We recommend that appropriate species for shoreland restoration efforts be selected based on the native plant communities present at the undeveloped sites, their relative location along an upland to shallow water gradient, and, in some cases, soil characteristics.

Effects of methyl mercury exposure on the growth of juvenile common loons.

We conducted a dose–response laboratory study to quantify the level of mercury exposure associated with negative effects on the development of common loon chicks reared in captivity from hatch to 105 days. A dose regimen was implemented that provided exposure levels that bracketed relevant exposure levels of methyl mercury found in loon chicks across North America. We observed no overt signs of mercury toxicosis and detected no significant effect of dietary mercury exposure on growth or food consumption. However, asymptotic mass was lower in chicks that hatched from eggs collected from nests on low pH lakes relative to eggs from neutral pH lakes. Rapid excretion of methyl mercury during feather growth likely provides loon chicks protection from methyl mercury toxicity and may explain the lack of convincing toxicological findings in this study. Lake-source effects suggest that in ovo exposure to methyl mercury or other factors related to lake pH have consequences on chick development.

PROTEIN AND ENERGY CONTENT OF WHITE-TAILED DEER DIETS IN THE TEXAS COASTAL BEND

The monthly botanical composition of diets selected by five adult white-tailed deer (Odocoileus virginianus) in a 24-ha enclosure was determined from October 1980-September 1981 using the bite-count method. Samples of plant species consumed were analyzed for crude protein (CP) and in vitro digestible energy (DE). Browse made up 50-70% of the diets in autumn (Oct-Dec) and July. Forbs accounted for 52- 88% of the January-April and September intake. Grasses comprised 35-42% of the May and June forage. Browse maintained the highest CP content and forbs the highest DE values. Dietary CP ranged from a maximum of 19% in February and March to a low of 10% in August. Dietary DE content ranged from 2.70 kcal/g DM in February to 1.77 kcal in July. Results indicate that the marginal quality of late summer diets may limit white-tailed deer populations in the Coastal Bend region of Texas.