Tatjana Krama

Evidence for the stress-linked immunocompetence handicap hypothesis in humans

Secondary sexual traits that develop under the action of testosterone, such as masculine human male facial characteristics, have been proposed to signal the strength of the immune system due to the sex hormones immunosuppressive action. Recent work has suggested that glucocorticoid stress hormones may also influence expression of such sexual signals due to their effects on immune function. Precise roles, however, remain unclear. Here we show positive relationships between testosterone, facial attractiveness and immune function (antibody response to a hepatitis B vaccine) in human males, and present some preliminary evidence that these relationships are moderated by naturally co-occurring cortisol (a glucocorticoid stress hormone involved in the fight-or-flight response). We conclude that our results provide support for a role of glucocorticoids in hormonally mediated sexual selection.

Interspecific reciprocity explains mobbing behaviour of the breeding chaffinches, Fringilla coelebs

When prey animals discover a predator close by, they mob it while uttering characteristic sounds that attract other prey individuals to the vicinity. Mobbing causes a predator to vacate its immediate foraging area, which gives an opportunity for prey individuals to continue their interrupted daily activity. Besides the increased benefits, mobbing behaviour also has its costs owing to injuries or death. The initiator of mobbing may be at increased risk of predation by attracting the predators attention, especially if not joined by other neighbouring prey individuals. Communities of breeding birds have always been considered as temporal aggregations. Since an altruist could not prevent cheaters from exploiting its altruism in an anonymous community, this excluded any possibility of explaining mobbing behaviour in terms of reciprocal altruism. However, sedentary birds may have become acquainted since the previous non–breeding season. Migrant birds, forming anonymous communities at the beginning of the breeding season, may also develop closer social ties during the course of the breeding season. We tested whether a male chaffinch, a migrant bird, would initiate active harassment of a predator both at the beginning of the breeding season and a week later when it has become a member of a non–anonymous multi–species aggregation of sedentary birds. We expected that male chaffinches would be less likely to initiate a mob at the beginning of the breeding season when part of an anonymous multi–species aggregation of migratory birds. However, their mobbing activity should increase as the breeding season advances. Our results support these predictions. Cooperation among individuals belonging to different species in driving the predator away may be explained as interspecific reciprocity based on interspecific recognition and temporal stability of the breeding communities.

Linking social complexity and vocal complexity: a parid perspective

The Paridae family (chickadees, tits and titmice) is an interesting avian group in that species vary in important aspects of their social structure and many species have large and complex vocal repertoires. For this reason, parids represent an important set of species for testing the social complexity hypothesis for vocal communication—the notion that as groups increase in social complexity, there is a need for increased vocal complexity. Here, we describe the hypothesis and some of the early evidence that supported the hypothesis. Next, we review literature on social complexity and on vocal complexity in parids, and describe some of the studies that have made explicit tests of the social complexity hypothesis in one parid—Carolina chickadees, Poecile carolinensis. We conclude with a discussion, primarily from a parid perspective, of the benefits and costs of grouping and of physiological factors that might mediate the relationship between social complexity and changes in signalling behaviour.

Adiposity, compared with masculinity, serves as a more valid cue to immunocompetence in human mate choice

According to the ‘good genes’ hypothesis, females choose males based on traits that indicate the males genetic quality in terms of disease resistance. The ‘immunocompetence handicap hypothesis’ proposed that secondary sexual traits serve as indicators of male genetic quality, because they indicate that males can contend with the immunosuppressive effects of testosterone. Masculinity is commonly assumed to serve as such a secondary sexual trait. Yet, women do not consistently prefer masculine looking men, nor is masculinity consistently related to health across studies. Here, we show that adiposity, but not masculinity, significantly mediates the relationship between a direct measure of immune response (hepatitis B antibody response) and attractiveness for both body and facial measurements. In addition, we show that circulating testosterone is more closely associated with adiposity than masculinity. These findings indicate that adiposity, compared with masculinity, serves as a more important cue to immunocompetence in female mate choice.

Predation selects for low resting metabolic rate and consistent individual differences in anti-predator behavior in a beetle

Significant between-individual variation in resting metabolic rate (RMR) of animals is a widespread phenomenon that may have important implications for our understanding of variation in behavior and animal personality. By using wild caught mealworm beetles, Tenebrio molitor, we examined the relationships among survival rate under predator tests, individual response latency time to become immobile under the risk of predation, duration of immobility time, and RMR. Individuals with higher levels of RMR were bold, and bold individuals were found to be more exposed to the risk of bird predation. We found that RMR was positively correlated with the latency of immobility response and negatively correlated with the total duration of immobility. The correlation between behavioral responses suggests a behavioral syndrome in the anti-predator behavior of T. molitor. The results indicate that energy metabolism may be part of a syndrome that involves behavior and life history traits in animals.

Heterophil/lymphocyte ratios predict the magnitude of humoral immune response to a novel antigen in great tits (Parus major).

Animals display remarkable individual variation in their capacity to mount immune responses against novel antigens. According to the life-history theory, this variation is caused by the costs of immune responses to the hosts. We studied one of such potential costs, depletion of somatic resources in wintering wild-caught captive passerines, the great tits (Parus major) by immune challenging the birds with a novel antigen, killed Brucella abortus (BA) suspension. We found that despite mild temperature conditions in captivity and ad libitum availability of food, immune challenge depleted somatic resources (as indicated by a body mass loss) and elevated relative proportion of heterophils to lymphocytes (H/L ratio) in the peripheral blood of birds. However, body mass loss did not covary with an increase in H/L ratios between two sampling events, which indicates that these two markers of health state describe different aspects of individual physiological condition. Antibody titres were not associated with the extent of body mass loss during the development of immune response, which shows that the somatic cost of immune response was not proportional to the amount of antibody produced. Birds with high pre-immunisation H/L ratios mounted weaker antibody response, which is indicative of stress-induced suppression of humoral immune response and is consistent with the concept of an antagonistic cross-regulation between different components of the immune system. The latter finding suggests a novel diagnostic value of H/L ratios, which reinforces the utility of this simple haematological index for prediction of the outcomes of complicated immune processes.

Group effect in nest defence behaviour of breeding pied flycatchers, Ficedula hypoleuca

Many group-living animals approach and mob nest predators, since grouping can increase the effectiveness of defence against predators. Some nonexperimental evidence shows that the intensity of harassment of predators increases with increasing mob size, indicating a group size effect for mobbing. In this field study we tested whether the intensity of mobbing depends on breeding group size in semicolonially breeding pied flycatchers. We recorded nest defence by parents when chicks were at least 8 days old and again 4 days later. When group size decreased naturally between the first and second trials, the intensity of mobbing a stuffed owl by the nest owners decreased. In contrast, when the number of neighbours remained unchanged the intensity of mobbing by nest owners increased significantly in the second trial. These results reveal the importance of group size in mobbing, indicating that the mobbing behaviour of the first individuals to mob is influenced by the presence of other mobbing conspecific individuals.

Effects of food quality on trade-offs among growth, immunity and survival in the greater wax moth Galleria mellonella

The resources available to an individual in any given environment are finite, and variation in life history traits reflect differential allocation of these resources to competing life functions. Nutritional quality of food is of particular importance in these life history decisions. In this study, we tested trade‐offs among growth, immunity and survival in 3 groups of greater wax moth (Galleria mellonella) larvae fed on diets of high and average nutritional quality. We found rapid growth and weak immunity (as measured by encapsulation response) in the larvae of the high‐energy food group. It took longer to develop on food of average nutritional quality. However, encapsulation response was stronger in this group. The larvae grew longer in the low‐energy food group, and had the strongest encapsulation response. We observed the highest survival rates in larvae of the low‐energy food group, while the highest mortality rates were observed in the high‐energy food group. A significant negative correlation between body mass and the strength of encapsulation response was found only in the high‐energy food group revealing significant competition between growth and immunity only at the highest rates of growth. The results of this study help to establish relationships between types of food, its nutritional value and life history traits of G. mellonella larvae.

Extremely low ambient temperature affects haematological parameters and body condition in wintering Great Tits (Parus major)

In high latitudes, thermoregulatory and behavioural adjustments of birds allow survival under extreme ambient temperatures, changing day length, and food availability. In such habitats with such fluctuating environmental conditions, dominant individuals in social species often monopolise safe microhabitats and food resources, which may lead to greater levels of stress in subordinates. The results of this study revealed that certain haematological indices of health state and body condition of wintering Great Tits (Parus major) were dependent on their sex and age under conditions of extreme ambient temperature. Heterophil and lymphocyte counts revealed a significant increase in heterophil/lymphocyte ratio (H/L) in female Great Tits during the course of cold spell, where the increase was detected mainly in the first year females. We also found that the condition of pectoral muscle during the cold spells deteriorated only in females, especially in the first year individuals. Since sex appears to be the most important predictor of the dominance rank and survival in Great Tit winter groups, elevated physiological stress in adult and first year females during cold spells may be explained in terms of increased resource monopolisation by dominant individuals.ZusammenfassungIn großen Höhen machen es Vögeln thermoregulatorische und verhaltensbiologische Anpassungen möglich, unter extremen Umgebungstemperaturen und veränderten Tageslängen und Futterverfügbarkeit zu überleben. In solchen Habitaten mit ihren schwankenden Umgebungsbedingungen monopolisieren innerhalb von sozialen Arten oft dominante Tiere sichere Mikrohabitate und Futterreserven, was bei den subdominanten Artgenossen zu erhöhtem Stress führen kann. Die Ergebnisse dieser Untersuchung machen deutlich, dass bestimmte hämatologische Anzeiger für den Gesundheitsstatus und die körperliche Verfassung überwinternder Kohlmeisen (Parus major) bei extremen Umgebungstemperaturen von ihrem Alter und ihrem Geschlecht abhängig waren. Zählungen von Heterophilen und Lymphozyten ergaben einen signifikanten Anstieg der Heterophilen/Lymphozyten-Rate (H/L) bei weiblichen Kohlmeisen während Kälteeinbrüchen, wobei dieser Anstieg in erster Linie bei den Weibchen vom gleichen Jahr festgestellt wurde. Wir fanden außerdem, dass sich der Zustand des Herzmuskels während dieser Kälteeinbrüche verschlechterte, allerdings nur bei Weibchen und da auch nur bei denen vom gleichen Jahr. Da bei den Wintergruppen der Kohlmeisen das Geschlecht der wichtigste Prädiktor für Dominanz und Überleben zu sein scheint, kann bei adulten Weibchen vom gleichen Jahr erhöhter Stress während Kälteeinbrüchen möglicherweise mit massiverer Ressource-Monopolisierung durch dominante Individuen erklärt werden.

Overwinter survival depends on immune defence and body length in male Aquarius najas water striders

Winter survival of organisms has a crucial effect on their fitness in a seasonal environment. We tested whether overwinter survival of male water striders, Aquarius najas (De Geer) (Heteroptera: Gerridae), is associated with the time of season they leave the water for winter diapause. This was performed by comparing parameters of males leaving the water at the beginning of autumn and 1 month later. The results show significantly higher overwinter survival in males of the early diapausing group. They were found to be larger than late diapausing individuals. Overall, overwinter survival was found to be associated with body length. The strength of immune defence measured as encapsulation response against nylon monofilament appeared to be stronger in the early than in the late dia‐pausing group. Body length had an effect on the encapsulation rates of water striders, with larger males having a stronger encapsulation response. The amount of lipids was larger in males of the early diapausing group, and the relationship between body length and absolute lipid reserves was positive in both groups. However, a correlation between body reserves and body length was not found when lipid content was expressed as a proportion of total body weight. The results suggest that body length is the main variable linking overwinter survival and resistance against pathogens and parasitoids. This study shows that differences in resistance can explain differential winter survival of larger and smaller A. najas water striders.