Robert L. Lochmiller

Relationship between protein nutritional status and immunocompetence in northern Bobwhite chicks

ABSmAcr.-We investigated the effects of dietary protein quality on the development and functioning of the immune system in four-week-old Northern Bobwhite (Colinus virginianus) chicks. Chicks were fed isocaloric diets containing 8, 15, or 33% protein over a three-week period. Significant reductions in the rate of body growth were evident in chicks receiving 8 and 15% protein. Development of the bursa of Fabricius and spleen was significantly depressed in the 8% protein group compared to the other two treatments. Lymphocyte yields from dissociated lymphoid organs of chicks fed 8% protein were substantially reduced compared to birds fed higher levels of protein. In vitro lymphoproliferative responses of cultured splenocytes to mitogenic stimulation (concanavalin A, pokeweed mitogen, and Salmonella typhimurium), white-blood-cell counts, and in vivo measures of humoral immunity did not differ among dietary treatments. Cell-mediated immune function, as measured by an in vivo hypersensitivity response to an intradermal injection of a T lymphocyte-dependent mitogen (phytohemagglutinin), was significantly suppressed in the 8% protein group compared to the other two treatments. Several measures of immune-system development and function were significantly correlated with body mass change during the trial. Results indicated that four-week-old Northern Bobwhite chicks fed an 8% protein diet for three weeks may have difficulty expressing a competent immune response to pathogenic challenge in the wild. Received 30 January 1992, accepted 25 November 1992.

MAJOR-HISTOCOMPATIBILITY-COMPLEX-ASSOCIATED VARIATION IN SECONDARY SEXUAL TRAITS OF WHITE-TAILED DEER (ODOCOILEUS VIRGINIANUS): EVIDENCE FOR GOOD-GENES ADVERTISEMENT

Abstract Good‐genes hypotheses predict that development of secondary sexual characters can be an honest advertisement of heritable male quality. We explored this hypothesis using a cervid model (adult, male white‐tailed deer, Odocoileus virginianus) to determine whether antler development could provide an honest signal of a males genetic quality and condition to adversaries. We compared antler, morphometric, hormonal, and parasitic data collected from hunter‐harvested deer to characteristics of the Mhc‐DRB (Odvi), the most widely studied gene of the major histocom‐patibility complex (MHC) in Artiodactyla. We detected associations between genetic characteristics at Odvi‐DRB and antler development and body mass, suggesting that antler development and body mass may be associated with pathogen resistance in deer and thus may be an honest signal of genetic quality. We also detected associations between Odvi‐DRB characteristics and serum testosterone during the breeding season, suggesting that certain MHC characteristics may help deer cope with stresses related to breeding activity. In addition, we observed a negative relationship between degree of antler development and overall abundance of abomasal helminths. Our observations provide support for the hypothesis that antler development in white‐tailed deer is an honest signal of quality.

Physiological correlates of neonatal mortality in an overpopulated herd of white-tailed deer

We examined the relationship of development, immunocompetence, and tick burdens to neonatal mortality in an overpopulated herd of white-tailed deer ( Odocoileus virginianus ) during 1990–1992 in northeastern Oklahoma. Risk of mortality to 21 days of age was inversely related to body mass, body mass/length3, delayed hypersensitivity to phytohem-agglutinin, and serum concentrations of gamma globulin and gamma-glutamyl transferase (GGTP) for young ≤3days old. Serum GGTP and gamma-globulin concentrations were the most significant predictors of mortality to 21 days of age using multivariate-logistic regression. Increased probability of mortality was associated with lower serum gamma globulin and concentrations of GGTP, which suggested that inadequate absorption of colostrum leads to a partial failure in the passive process of transferring immunity from mother to offspring, and predisposes young to mortality agents among high-density herds.

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.

In situ (mesocosm) assessment of immunotoxicity risks to small mammals inhabiting petrochemical waste sites

Oil refineries inadvertently deposit a variety of complex mixtures of organic hydrocarbons and heavy metals in the soil, many of which are thought to be potent immunotoxicants. Terrestrial ecosystems such as this have not been adequately investigated with respect to wild rodent populations. The primary objective of this study was to use mesocosms to assess the immunotoxicity risks to feral small mammal populations associated with soils contaminated with petroleum refinery wastes. A series of 4-week and 8-week exposure trials using laboratory raised cotton rats (Sigmodon hispidus) were conducted in situ on three contaminated and three reference sites on the Oklahoma Refining Company Superfund Waste Site, Cyril, Oklahoma. Cotton rats exposed to these soils showed significant alterations in selected morphological traits, in vivo humoral immune responses, complement activity, and macrophage activity. However, immune alterations were not great, suggesting that resident small mammals may be a better biomonitoring choice than using mesocosms.

VARIATION IN GASTROINTESTINAL CHARACTERISTICS OF MALE AND FEMALE WHITE-TAILED DEER: IMPLICATIONS FOR RESOURCE PARTITIONING

We assessed variation in intestinal lengths and gut capacity of white-tailed deer (Odocoileus virginianus). We hypothesized that differences in morphology of males and females could have important implications relative to intersexual variation in patterns of habitat use and forage acquisition. Deer were collected from study areas in McCurtain Co., Oklahoma, and Howard and Pike counties, Arkansas. Populations of white-tailed deer in McCurtain and Howard counties were in poorer nutritional condition than deer in Pike Co. possibly because of competitive interactions with cattle stocked on study areas in McCurtain and Howard counties. Lactating females had longer gastrointestinal tracts and more digesta within their rumens and intestines than did males in summer and winter. Lactating females also had longer intestinal tracts and more digesta in rumens and intestines than did pregnant females during winter. Nonpregnant females in winter were primarily fawns with low body mass, but did not differ from adult females or males relative to gastrointestinal characteristics. Females collected from Pike Co. in winter had less digesta in rumens and intestines than did other populations. Additionally, deer collected from Pike Co. in winter had proportionately less digesta in rumens and more digesta in intestines than other populations. Our findings indicated that sexual segregation of populations of white-tailed deer in summer results from females attempting to maintain maximum volume of digesta in gastrointestinal tracts; winter segregation might be influenced by dietary selection.

RISK FACTORS ASSOCIATED WITH CAPTURE-RELATED DEATH IN EASTERN WILD TURKEY HENS

Capture-related mortality has been a notable risk in the handling of eastern wild turkey (Meleagris gallopavo silvestris). Our objective was to evaluate how environmental factors influence risk and identify physiological correlates that could be used to identify susceptible birds. During winter (January–March) 1995–97, 130 eastern wild turkey hens were captured in southeastern Oklahoma and radiocollared. Of those, 20 hens died ≤14 days of capture. Serum creatine kinase activity (CK; P < 0.01), body temperature (P < 0.01), processing time (P = 0.02), and ambient temperature (P < 0.01) showed a positive relationship with mortality that occurred within 14 days of capture. Plasma corticosterone concentration (P = 0.08) and relative humidity (P < 0.01) showed a negative relationship with mortalities that occurred within 14 days post-capture. Stepwise logistic regression selected CK activity, relative humidity, and ambient temperature as the best predictors of mortality within 14 days post-capture. Our data suggest that susceptible individuals may be identified from CK activity and that capture-related mortality may be minimized by establishing guidelines of when to curtail capture operations based on various weather 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.

Concentrations of insulin-like growth factor-I in adult male white-tailed deer (Odocoileus virginianus): associations with serum testosterone, morphometrics and age during and after the breeding season

Our understanding of insulin-like growth factor-I (IGF-I) in cervids has been limited mostly to its effects on antler development in red deer (Cervus elaphus), roe deer (Capreolus capreolus), fallow deer (Dama dama), and pudu (Pudu puda). Although IGF-I has been found to play a critical role in reproductive function of other mammals, its role in reproduction of deer is unknown. The objectives of the present study were to determine if serum levels of IGF-I change during the breeding season, assess whether age influences serum IGF-I, compare levels of IGF-I measured during and following the breeding season, and determine if IGF-I is associated with body and antler characteristics in free-ranging adult, male white-tailed deer (Odocoileus virginianus). We collected serum and morphometric data from hunter-harvested and captured white-tailed deer to investigate these objectives. Mean level of serum IGF-I during the breeding season was 63.6 ng/ml and was greatest in deer between 2.5 and 5.5 years old (57.4-79.9 ng/ml). Levels of serum IGF-I decreased by approximately 40% as the breeding season progressed, but levels were less in deer following the breeding season (34.6 ng/ml). Both body and antler size were associated positively with IGF-I when controlling for age. Serum testosterone was also associated positively with IGF-I. Levels of serum testosterone during the breeding season generally increased with age from 4.82 (1.5 years old) to 18.79 ng/dl (5.5 years old), but decreased thereafter. These data suggest that IGF-I may be an important hormone in breeding, male white-tailed deer.

Age-specific causes of mortality among male white-tailed deer support mate-competition theory

Mate-competition theory predicts that males will invest resources toward intrasexual competition for mates until reproductive benefits are outweighed by costs to future fitness. In populations that have a substantial proportion of mature males, theory predicts that young males will forego reproduction to reduce exposure to mortality that may result from breeding efforts. We examined age-specific mortality of males in a white-tailed deer (Odocoileus virginianus) population in which >50% of the males were ≥3.5 years old to determine whether patterns of male mortality conform to mate-competition theory. Annual mortality rates were relatively stable throughout adulthood (0.26-0.38), but causes of mortality changed with age. Young males (1.5 and 2.5 years old) were most susceptible to human-induced mortality (e.g., hunting and vehicle accidents), whereas males ≥3.5 years old tended to die from non-human causes (e.g., fighting, predation) more frequently than did younger deer. Proportional hazard models also indicated that as antler size increased, likelihood of mortality increased. Age- and cause-specific patterns of mortality in adult male deer from a population with >50% mature males reflected patterns predicted by mate-competition theory. When managing deer populations with high proportions of mature males, it is important to account for shifts in susceptibility to human-induced and natural mortality agents.