Ilmari Jokinen

Do pheromones reveal male immunocompetence

Pheromones function not only as mate attractors, but they may also relay important information to prospective mates. It has been shown that vertebrates can distinguish, via olfactory mechanisms, major histocompatibility complex types in their prospective mates. However, whether pheromones can transmit information about immunocompetence is unknown. Here, we show that female mealworm beetles (Tenebrio molitor) prefer pheromones from males with better immunocompetence, indicated by a faster encapsulation rate against a novel antigen, and higher levels of phenoloxidase in haemolymph. Thus, the present study indicates that pheromones could transmit information about males parasite resistance ability and may work as a reliable sexual ornament for female choice.

Testosterone‐Mediated Effects on Fitness‐Related Phenotypic Traits and Fitness

The physiological and behavioral mechanisms underlying life‐history trade‐offs are a continued source of debate. Testosterone (T) is one physiological factor proposed to mediate the trade‐off between reproduction and survival. We use phenotypic engineering and multiple laboratory and field fitness‐related phenotypic traits to test the effects of elevated T between two bank vole Myodes glareolus groups: dominant and subordinate males. Males with naturally high T levels showed higher social status (laboratory dominance) and mobility (distance between capture sites) than low‐T males, and the effect of T on immune response was also T group specific, suggesting that behavioral strategies may exist in male bank voles due to the correlated responses of T. Exogenous T enhanced social status, mate searching (polygon of capture sites), mobility, and reproductive success (relative measure of pups sired). However, exogenous T also resulted in the reduction of immune function, but only in males from the high‐T group. This result may be explained either by the immunosuppression costs of T or by differential sensitivity of different behavioral strategies to steroids. Circulating T levels were found to be heritable; therefore, female bank voles would derive indirect genetic benefits via good genes from mating with males signaling dominance.

Biomarker responses along a pollution gradient: Effects of pulp and paper mill effluents on caged whitefish

Abstract Lake Saimaa (SE Finland) is a large oligotrophic lake receiving biologically treated effluent from a bleached kraft pulp and paper mill. Hatchery-reared juvenile whitefish ( Coregonus lavaretus L. s.l.), a species known to feed on plankton and other particulates, were caged using a technique developed and optimized for this species and were exposed for one month in five downstream stations (3.3–16 km). Two reference stations (4.5–8.5 km) upstream from the effluent outlet were used. An exposure gradient of chlorinated organics was assessed by determining concentrations of conjugated chlorophenolics (CPs) in bile and CPs as well as extractable organic halogens (EOX) in gut lipids. Activities of liver cytochrome P4501A (CYP1A) monooxygenase and two conjugation enzymes, uridinediphospho glucuronosyltransferase (UDP-GT) and glutathione S -transferase (GST), were measured as indicators of exposure. Humoral antibody (IgM) level in plasma was used to estimate immune capacity. Other blood parameters were also analyzed. Fish caged nearest the mill (3.3 km) had concentrations of CPs in bile 50-fold that of upstream reference fish. A gradual, distance-related, decrease of CPs in bile was seen. A similar trend was seen in EOX and concentrations of CPs in gut lipid. Induction of CYP1A, measured as activity of 7-ethoxyresorufin O -deethylase (EROD), was seen in fish at all downstream sites. At the site nearest the mill, EROD activity was 13-fold higher compared to the reference area. No significant changes were seen in liver UDP-GT or GST. Levels of plasma IgM were 58–97% of reference values in fish caged at downstream from the outfall. We conclude that biomarkers in this study implicated the effluent as a causal factor and that relative severity of exposure was inversely related to distance from the effluent source.

Optimal diet composition for European whitefish (Coregonus lavaretus): carbohydrate stress and immune parameter responses

Abstract A feeding trial was conducted on the European whitefish to study the effects of replacing fish meal with fish oil and corn starch on the stress response and immune system parameters. Nine diets with varying levels of fish meal (FM; 38–86%), fish oil (FO; 2–22%) and corn starch (CS; 0–33%), and fixed levels of wheat meal (10%) and vitamin–mineral premix (2%) were formulated and replicates were allocated among 25 tanks following the D-optimality criteria. Fish were fed the extruded diets to satiation for 10 weeks in a flow-through freshwater system at 15 °C. The liver and plasma were sampled at the termination of the trial, and the response surfaces were modeled as Scheffe polynomials specific for mixture designs. Liver glycogen and plasma glucose increased and plasma IgM decreased with increasing CS level. Plasma lysozyme levels decreased with an increase in FM. Plasma cortisol showed a linear response, with the highest values in high-FO, low-CS diets. Mortalities only occurred with high-CS diets. After the feeding trial, the effects of rapid water cooling on stress responses were measured in fish fed either a low-starch diet (66% FM, 22% FO, and 0% CS) or a high-starch diet (53% FM, 2% FO, and 33% CS). Initial plasma samples were collected at 15 °C, whereafter the temperature was reduced to 2 °C in 24 h. Plasma samples were withdrawn, and sampling was repeated after three more days at 2 °C. Cortisol increased from an initial 7 to a peak value of 70 ng ml −1 at the second sampling, and decreased thereafter to 20–30 ng ml −1 . Plasma glucose increased from an initial 3.9 to 4.8 mmol l −1 after 24 h, and further increased to approximately 7.8 mmol l −1 after three more days in cold water. The responses did not differ significantly between fish fed low-starch or high-starch diets. On overall, whitefish showed inadequate adaptation to high dietary carbohydrate levels.

FITNESS TRADE-OFFS MEDIATED BY IMMUNOSUPPRESSION COSTS IN A SMALL MAMMAL

Trade‐offs are widespread between life‐history traits, such as reproduction and survival. However, their underlying physiological and behavioral mechanisms are less clear. One proposed physiological factor involves the trade‐off between investment in male reproductive effort and immunity. Based on this hypothesis, we investigated differences in fitness between artificially selected immune response bank vole groups, Myodes glareolus. Significant heritability of immune response was found and a correlated response in testosterone levels to selection on immune function. Male reproductive effort, reproductive success, and survival of first generation offspring were assessed and we demonstrate a relationship between laboratory measured immune parameters and fitness parameters in field enclosures. We identify a trade‐off between reproductive effort and survival with immune response and parasites as mediators. However, this trade‐off results in equal male fitness in natural conditions, potentially demonstrating different male signaling strategies for either reproductive effort or survival. Females gain indirect genetic benefits for either genetic disease resistance or male reproductive effort, but not both. Immune response is genetically variable, genetically linked to testosterone and may indirectly maintain genetic variation for sexually selected traits. Evidence for both a genetic and a field trade‐off between reproductive effort and survival indicates an evolutionary constraint on fitness traits.

Is the antipredatory response in behaviour reflected in stress measured in faecal corticosteroids in a small rodent

Predation risk has been shown to alter various behaviours in prey. Risk alters activity, habitat use and foraging, and weight decrease might be a consequence of that. In mammals, studies on physiological measures affected by risk of predation, other than weight, are rare. We studied in two separate laboratory experiments foraging, hoarding behaviour and expression of stress measured non-invasively from the faeces in the bank vole (Clethrionomys glareolus), a common boreal rodent. Voles were exposed to predation risk using odours of the least weasels (Mustela nivalis nivalis). Distilled water served as control. In the first experiment, we found that foraging effort, measured as sunflower seeds taken from seed trays filled with sand, was significantly lower in trays scented with weasel odour. Both immediate consumption of seeds and hoarding were affected negatively by the weasel odour. Females hoarded significantly more than males in autumn. In the second experiment, the negative effect of weasel odour on foraging was consistent over a 3-day experiment, but the strongest effect was observed in the first night. Foraging increased over the time of the experiment, which might reflect either energetic compensation during a longer period of risk, predicted in the predation risk allocation hypothesis, or habituation to the odour-simulated risk. Despite decreased foraging under predation risk, stress measured as corticosteroid metabolite concentration in vole faeces was not affected by the weasel odour treatment. In conclusion, we were able to verify predation-risk-mediated changes in the foraging effort of bank voles but no physiological stress response was measured non-invasively, probably due to great individual variation in secretion of stress hormones.

Intra‐ and Intersexual Trade‐Offs between Testosterone and Immune System: Implications for Sexual and Sexually Antagonistic Selection

Parasites indirectly affect life‐history evolution of most species. Combating parasites requires costly immune defenses that are assumed to trade off with other life‐history traits. In vertebrate males, immune defense is thought to trade off with reproductive success, as androgens enhancing sexual signaling can suppress immunity. The phenotypic relationship between male androgen levels and immune function has been addressed in many experimental studies. However, these do not provide information on either intra‐ or intersex genetic correlations, necessary for understanding sexual and sexually antagonistic selection theories. We measured male and female humoral antibody responses to a novel antigen (bovine gamma globulin), total immunoglobulin G, and the male testosterone level of a laboratory population of the bank vole (Myodes glareolus). Although we studied five traits, factor‐analytic modeling of the additive genetic (co)variance matrix within a restricted maximum likelihood–animal model supported genetic variation in three dimensions. Sixty‐five percent of the genetic variation contrasted testosterone with both immune measures in both sexes; consequently, selection for the male trait (testosterone) will have correlated effects on the immune system not only in males but also in females. Thus, our study revealed an intra‐ and intersexual genetic trade‐off between immunocompetence and male reproductive effort, of which only indirect evidence has existed so far.

The efficacy of two immunostimulants against Flavobacterium columnare infection in juvenile rainbow trout (Oncorhynchus mykiss)

Bacterium Flavobacterium columnare is the causative agent of columnaris disease in many wild and farmed fish species. Immunostimulants are used with success in aquaculture against many pathogens, but the ability to improve innate resistance to columnaris disease has not been studied. Fingerling rainbow trout were treated with two immunostimulants, yeast beta-glucan and beta-hydroxy-beta-methylbutyrate (HMB). Selected innate immune function parameters, the production of reactive oxygen species (ROS) by whole blood and by isolated head kidney leukocytes, plasma lysozyme activity and complement bacteriolytic activity, were determined to assess the immune status of fish. The fish were then bath challenged with virulent F. columnare bacteria, and the mortality of fish was recorded. Given orally both stimulants raised the levels of immune function parameters, but did not improve survival in challenge at any concentration of the stimulants used. Intra peritoneal injection of beta-glucan increased parameter values several fold, but no beneficial effect of injected glucan on survival was noted. As a control, antibiotic medication administered prior to and during the challenge infection prevented the mortality. Innate immune mechanisms, even when induced to high levels with immunostimulants, as evidenced here, were not able to increase resistance against F. columnare. This may be connected to the external character of the infection. The results from the treatments with beta-glucan and HMB suggest that there is little prospect of preventing columnaris disease by means of immunostimulants in early life stage of rainbow trout. However, the efficacy of other immune stimulants remains open.

GENETIC AND ENVIRONMENTAL VARIATION IN ANTIBODY AND T-CELL MEDIATED RESPONSES IN THE GREAT TIT

Abstract Host parasite coevolution assumes pathogen specific genetic variation in host immune defense. Also, if immune function plays a role in the evolution of life history, allocation to immune function should be heritable. We conducted a cross‐fostering experiment to test the relative importance of genetic and environmental sources of variation in T‐cell mediated inflammatory response and antigen specific antibody responses in the great tits Parus major. Cell mediated response was measured during the nestling period and antibody response against two novel antigens was measured in two‐month‐old juveniles raised in a laboratory. We found no effect of nest of origin, but a strong effect of rearing environment on cell mediated response. In contrast, we found a large effect of nest of origin on antibody response to both, diphtheria and tetanus antigens suggesting genetic variation. In a model where responses to both antigens were analyzed simultaneously, we found a significant origin‐by‐antigen interaction, suggesting that genetic variation in antibody responses is specific to particular antigens. Large genetic variation in antibody responses found in this study suggests that host immune defense may evolve and specificity of genetic variation in antibody responses suggests that host defense may be pathogen specific as models of host‐parasite coevolution suggest. Our results also suggest that different immune traits are to some degree independent and outcome of the interactions between immune function and the environment may depend on the particular immune trait measured.

Exposure to Increased Ambient Ultraviolet B Radiation has Negative Effects on Growth, Condition and Immune Function of Juvenile Atlantic Salmon (Salmo salar)

Atlantic salmon (Salmo salar) parr were exposed in two outdoor experiments, ranging in duration from 52 to 137 days, to spectral treatments: (1) natural sunlight (=present ambient UVB level), (2) solar radiation supplemented with enhanced UVB radiation from lamps simulating 20% or 8% stratospheric ozone loss or (3) UVB‐depleted sunlight achieved by screening with Mylar‐D film. The growth, condition and immune function of the salmon were quantified after treatments. Exposure to enhanced UVB radiation retarded growth, and decreased hematocrit value and plasma protein concentration. Further, enhanced UVB radiation affected plasma immunoglobulin concentration. The results demonstrate that juvenile Atlantic salmon are not able to fully adapt to increased ambient UVB levels in long‐term exposures, and the interference with immune system function suggests a negative effect of UVB on disease resistance in Atlantic salmon.