Scott T. McMurry

Temporal variation in humoral and cell-mediated immune response in a Sigmodon hispidus population

We examined the hypothesis that environmentally induced alteration of immunocompetence is a primary physiological mechanism by which population survival is regulated. The involvement of disease and immunocompetence in the regulation of small mammal populations is not well understood but a strong relationship between physiological stress and immunity has been demonstrated. Its involvement is further supported by several studies, which have provided evidence that survival, incidence of disease, and selected gross measures of immunity change temporally with density and season. We examined this hypothesis by documenting the existence of temporal alterations in selected measures of both humoral and cell-mediated immune function in a population of cotton rats (Sigmodon hispidus), a species known to fluctuate widely in density, inhabiting a tallgrass prairie in central Oklahoma. A total of 3 10 cotton rats was collected from August 1989 to May 1991 (10 collections) using conventional live-trap methods. In addition to morphological char- acteristics of primary and secondary lymphoid organs, the ability of splenocytes to produce specific antibody in response to a single injection of sheep erythrocytes and to proliferate in response to in vitro exposure to mitogens was measured to assess immunocompetence. Whole blood was collected for the determination of total peripheral blood leukocyte counts, packed cell volume, and total serum proteins. Statistically significant differences in all variables except total serum protein existed among the 10 collections and most of this variability was independent of specific seasonal time periods. Bimodal rhythmicity was characteristic of temporal changes for several measures of immunocompetence. Changes over time in the average immunocompetence of this population could have reflected a shift in genotypic polymorphism; several other plausible explanations are offered to explain the observed temporal patterns.

Acute toxicity of fungicide formulations to amphibians at environmentally relevant concentrations

Fungicide use on row crops is increasing dramatically due to promotion of these products for general plant health and increased yield even during low disease pressure. These fungicides are applied aerially, which may lead to amphibian exposure within fields or in nearby habitat. Exposure to three of these fungicides at environmentally relevant conditions resulted in mortality for Bufo tadpoles and juveniles for two of the fungicides. Headline®, the most commonly used on row crops, resulted in >50% mortality for juveniles at corn label application rates and 100% mortality for tadpoles at one-tenth the label rate for corn. Stratego® killed 40% of exposed tadpoles on average at the corn label rate, but only 7% of the juveniles. Overall, Quilt® appeared less toxic than the other fungicides, resulting in 7 to 10% mortality of tadpoles and 4 to 22% mortality of juveniles at all concentrations (from 0.1× to 10× label rate). These fungicides, especially Headline, may pose a major hazard for amphibians exposed as tadpoles and/or juveniles at environmentally relevant concentrations.

INFLUENCES OF LAND USE AND WETLAND CHARACTERISTICS ON WATER LOSS RATES AND HYDROPERIODS OF PLAYAS IN THE SOUTHERN HIGH PLAINS, USA

More than 25,000 playa wetlands are embedded in the Southern High Plains (SHP), USA. The SHP is one of the most intensively cultivated areas in the world and, as a result, the function of playas has been altered by deposition of eroded sediments. We monitored water levels in 33 playas in summer 2003 to examine the influence of land use (cropland vs. native grassland) and playa characteristics (playa area, watershed size, starting water level, volume loss, sediment depth, percent playa vegetation cover, and soil texture zone) on water loss rate and hydroperiod (consecutive days a playa held measurable surface water). Multiple regression models (selected using Akaike’s Information Criterion) indicated that land use, percent playa vegetation cover, and soil texture zone were important factors explaining water loss rate while starting water level and land use were important in explaining hydroperiod. Playas with cropland watersheds have lost their hydric soil-defined volume due to sedimentation, which results in an increase in water surface area and evaporation, and possibly infiltration, thus shortening hydroperiod. Hydroperiod was not related to playa area. Based on hydroperiod, small playas should receive the same conservation consideration as larger playas. Future research should examine transpiration rates in playas within grassland and cropland landscapes.

Ecosystem services provided by playas in the High Plains: potential influences of USDA conservation programs

Playas are shallow depressional wetlands and the dominant wetland type in the non-glaciated High Plains of the United States. This region is one of the most intensively cultivated regions in the Western Hemisphere, and playas are profoundly impacted by a variety of agricultural activities. Conservation practices promoted through Farm Bills by the U.S. Department of Agriculture (USDA) that influence playas and surrounding catchments impact ecosystem functions and related services provided by wetlands in this region. As part of a national assessment, we review effects of agricultural cultivation and effectiveness of USDA conservation programs and practices on ecosystem functions and associated services of playas. Services provided by playas are influenced by hydrological function, and unlike other wetland types in the United States, hydrological function of playas is impacted more by accumulated sediments than drainage. Most playas with cultivated catchments have lost greater than 100% of their volume from sedimentation causing reduced hydroperiods. The Conservation Reserve Program (CRP) has the largest influence on playa catchments (the High Plains has >2.8 million ha), and associated sedimentation, of any USDA program. Unfortunately, most practices applied under CRP did not consider restoration of playa ecosystem function as a primary benefit, but rather established dense exotic grass in the watersheds to reduce soil erosion. Although this has reduced soil erosion, few studies have investigated its effects on playa hydrological function and services. Our review demonstrates that the Wetlands Reserve Program (WRP) has seldom been applied in the High Plains outside of south-central Nebraska. However, this is the primary program that exists within the USDA allowing conservation practices that restore wetland hydrology such as sediment removal. In addition to sediment removal, this practice has the greatest potential effect on improving hydrologic function by reducing sedimentation in vegetative buffer strips. We estimate that a 50-m native-grass buffer strip could improve individual playa hydroperiods by up to 90 days annually, enhancing delivery of most natural playa services. The potential for restoration of playa services using USDA programs is extensive, but only if WRP and associated practices are promoted and playas are considered an integral part of CRP contracts.

Effects of landuse and precipitation on pesticides and water quality in playa lakes of the southern high plains

The 25000 playa wetlands within the Southern High Plains (SHP) of the United States of America (USA) are the dominant hydrogeomorphic feature in the region, providing habitat for numerous plants and wildlife. The SHP are among the most intensively cultivated regions; there are concerns over the degradation and/or loss of playa wetland habitat. We examined water quality in playa wetlands surrounded by both grassland and agriculture and measured water concentrations of pesticides used on cotton (acephate, trifluralin, malathion, pendimethalin, tribufos, bifenthrin, λ-cyhalothrin, acetamiprid, and thiamethoxam), the dominant crop in the SHP. Pesticides used on cotton were detected in water samples collected from all playas. Precipitation events and the amount of cultivation were related to pesticide concentrations in sediment and water. Our results show that pesticide concentrations were related in some circumstances to time, precipitation, and tilled-index for some but not all pesticides. We further compared measured pesticide concentrations in playas to toxicity benchmarks used by the US EPA in pesticide ecological risk assessments to obtain some insight into the potential for ecological effects. For all pesticides in water, the maximum measured concentrations exceeded at least one toxicity benchmark, while median concentrations did not exceed any benchmarks. This analysis indicates that there is a potential for adverse effects of pesticides to aquatic organisms.

Toxicity of a glufosinate- and several glyphosate-based herbicides to juvenile amphibians from the Southern High Plains, USA

Pesticide toxicity is often proposed as a contributing factor to the world-wide decline of amphibian populations. We assessed acute toxicity (48 h) of a glufosinate-based herbicide (Ignite 280 SL) and several glyphosate-based herbicide formulations (Roundup WeatherMAX, Roundup Weed and Grass Killer Super Concentrate, Roundup Weed and Grass Killer Ready-To-Use Plus on two species of amphibians housed on soil or moist paper towels. Survival of juvenile Great Plains toads (Bufo cognatus) and New Mexico spadefoots (Spea multiplicata) was reduced by exposure to Roundup Weed and Grass Killer Ready-To-Use Plus on both substrates. Great Plains toad survival was also reduced by exposure to Roundup Weed and Grass Killer Super Concentrate on paper towels. New Mexico spadefoot and Great Plains toad survival was not affected by exposure to the two agricultural herbicides (Roundup WeatherMAX and Ignite 280 SL) on either substrate, suggesting that these herbicides likely do not pose an immediate risk to these species under field conditions.

Sensitivity of selected immunological, hematological, and reproductive parameters in the cotton rat (Sigmodon hispidus) to subchronic lead exposure.

The effect of lead exposure on cellular immunity, hematology, and reproductive and body condition in mature cotton rats (Sigmodon hispidus) was examined. Two groups of 36 cotton rats each were exposed to 0, 100, or 1,000 ppm lead in drinking water for either 7 or 13 weeks, between 31 August and 2 December 1990. Specific and non-specific cell mediated immunity was assessed by measuring splenocyte proliferative responses to polyclonal mitogens (Concanavalin A and Pokeweed mitogen), in vivo 24-hr delayed type hypersensitivity, metabolic activity of peritoneal macrophages, spleen mass and cellularity, and immune organ development. General physiological condition was assessed from hematological, morphological, and reproductive measures. Immune function was sensitive to lead exposure based on depressed proliferative responses of cultured splenocytes, smaller popliteal lymph nodes, and larger spleens among cotton rats receiving 1,000 ppm lead. Spleen mass was reduced in cotton rats receiving 100 ppm lead. Total leukocytes, lymphocytes, neutrophils, eosinophils, total splenocyte yield, packed cell volume, hemoglobin, and mean corpuscular hemoglobin were sensitive to lead exposure. Effects of lead exposure on general condition and reproductive parameters included reduced mass of liver, seminal vesicles, and epididymes in males following a 7-week exposure. Histopathologic changes reflected lead toxicity and included altered renal proximal tubular epithelium, renal intranuclear inclusions, and in some cases, lowered numbers of sperm and developing follicles. In general, lesions were more pronounced with increased lead concentration and longer exposure.

Size estimation, morphometrics, sex ratio, sexual size dimorphism, and biomass of Morelet's crocodile in northern Belize

Abstract. We used morphometric data from 1276 Crocodylus moreletii captured in northern Belize (1992–2001) to develop predictive models for determining body size (total length [TL], snout-vent length [SVL]) from measurements of single attributes (dorsal cranial length [DCL], cranial width [CW], snout length [SL] and width [SW], body mass [BM], rear-foot length [RFL]), quantify sexual size dimorphism, examine ontogenetic changes in cranial morphology, re-evaluate maximum body size attained by this species, and estimate standing crop biomass of crocodiles at our principal study site. Strong positive allometric relationships were found between measures of body length and other morphometric attributes, and provide a reliable means to estimate body length from tracks, skulls, and body parts. The maximum DCL:CW ratio is attained at a relatively small body size and preceded a dietary shift from insects and arachnids to vertebrates and ampullarid snails. The SL:SW ratio of C. moreletii is highly variable and because of overlap with C. acutus, deemed of little value for distinguishing these two sympatric species. Both overall and adult sex ratio (female:male) was male biased and differed significantly from parity. The mean SVL of adult males (98.3 ± 21.3 cm) was significantly greater than that of adult females (87.3 ± 15.9 cm). A compressed sexual size dimorphism index (SDI) of 2.12 was calculated for C. moreletii in northern Belize. Based on skull measurements, the current size record for C. moreletii in Belize is 362 cm TL. Standing crop biomass of C. moreletii at our principal study site (Gold Button Lagoon) was estimated to be 9.5 kg/ha.

Genetic diversity, population subdivision, and gene flow in Morelet's crocodile (Crocodylus moreletii) from Belize, central America

Abstract The lack of information surrounding natural history and ecology of the endangered Morelets crocodile (Crocodylus moreletii) has prompted a baseline study of the population genetics for this species. Nine microsatellite loci have been used to estimate genetic structure within and gene flow patterns among crocodiles (using a recently described maximum likelihood approach) from seven localities in north-central Belize. Individuals from the seven localities grouped into four apparent populations. Within localities, a high degree of genetic heterogeneity was observed. Among all localities, some subdivision was present (FST = 0.062; RST = 0.100). Furthermore, among the apparent populations, we found a significant correlation between geographic distance and genetic subdivision. Our findings suggest a relatively high level of migration among populations (Nm = 5.15) and are consistent with an isolation-by-distance model of gene flow. Two contiguous subpopulations in particular, New River and New River Lagoon, may form an important source for genetic variation for smaller populations throughout the region. These data will allow us to test hypotheses of relatedness among C. moreletii for other drainages in Belize and will be useful in optimizing future management programs for C. moreletii.

Assessment of the Effects of Farming and Conservation Programs on Pesticide Deposition in High Plains Wetlands

We examined pesticide contamination in sediments from depressional playa wetlands embedded in the three dominant land-use types in the western High Plains and Rainwater Basin of the United States including cropland, perennial grassland enrolled in conservation programs (e.g., Conservation Reserve Program [CRP]), and native grassland or reference condition. Two hundred and sixty four playas, selected from the three land-use types, were sampled from Nebraska and Colorado in the north to Texas and New Mexico in the south. Sediments were examined for most of the commonly used agricultural pesticides. Atrazine, acetochlor, metolachlor, and trifluralin were the most commonly detected pesticides in the northern High Plains and Rainwater Basin. Atrazine, metolachlor, trifluralin, and pendimethalin were the most commonly detected pesticides in the southern High Plains. The top 5-10% of playas contained herbicide concentrations that are high enough to pose a hazard for plants. However, insecticides and fungicides were rarely detected. Pesticide occurrence and concentrations were higher in wetlands surrounded by cropland as compared to native grassland and CRP perennial grasses. The CRP, which is the largest conservation program in the U.S., was protective and had lower pesticide concentrations compared to cropland.