People who are more avoidant of pathogens are more politically conservative, as are nations with greater parasite stress. In the current research, we test two prominent hypotheses that have been proposed as explanations for these relationships. The first, which is an intragroup account, holds that these relationships between pathogens and politics are based on motivations to adhere to local norms, which are sometimes shaped by cultural evolution to have pathogenneutralizing properties. The second, which is an intergroup account, holds that these same relationships are based on motivations to avoid contact with outgroups, who might pose greater infectious disease threats than ingroup members. Results from a study surveying 11,501 participants across 30 nations are more consistent with the intragroup account than with the intergroup account. National parasite stress relates to traditionalism (an aspect of conservatism especially related to adherence to group norms) but not to social dominance orientation (SDO; an aspect of conservatism especially related to endorsements of intergroup barriers and negativity toward ethnic and racial outgroups). Further, individual differences in pathogen-avoidance motives (i.e., disgust sensitivity) relate more strongly to traditionalism than to SDO within the 30 nations.political ideology | pathogens | disgust | culture | evolutionary psychology T he costs imposed by pathogens on their hosts have spurred the evolution of complex antipathogen defenses, many of which are behavioral (1, 2). In humans, such defenses range from the proximate avoidance of pathogen cues to the execution of complex rituals, often with far-reaching consequences (3). At the individual level, functionally specialized psychological mechanisms detect pathogen cues and motivate avoidance of physical contact with pathogens [e.g., via the emotion of disgust (4)]. These mechanisms, which have been collectively referred to as the behavioral immune system, influence, among other things, mate preferences (5, 6), dietary preferences (7), and person perception (8) (summarized in Significance Pathogens, and antipathogen behavioral strategies, affect myriad aspects of human behavior. Recent findings suggest that antipathogen strategies relate to political attitudes, with more ideologically conservative individuals reporting more disgust toward pathogen cues, and with higher parasite stress nations being, on average, more conservative. However, no research has yet adjudicated between two theoretical accounts proposed to explain these relationships between pathogens and politics. We find that national parasite stress and individual disgust sensitivity relate more strongly to adherence to traditional norms than they relate to support for barriers between social groups. These results suggest that the relationship between pathogens and politics reflects intragroup motivations more than intergroup motivations.

Problems in species recognition are thought to affect the evolution of secondary sexual characters mainly through avoidance of maladaptive hybridization. Another, but much less studied avenue for the evolution of sexual characters due to species recognition problems is through interspecific aggression. In the damselfly, Calopteryx splendens, males have pigmented wing spots as a sexual character. Large‐spotted males resemble males of another species, Calopteryx virgo, causing potential problems in species recognition. In this study, we investigate whether there is character displacement in wing spot size and whether interspecific aggression could cause this pattern. We found first that wing spot size of C. splendens in populations decreased with increasing relative abundance of C. virgo. Secondly, C. virgo males were more aggressive towards large‐ than small‐spotted C. splendens males. Thirdly, in interspecific contests C. virgo males had better territory holding ability than C. splendens males. These results suggest that interspecific aggression may have caused character displacement in wing spot size of C. splendens, because the intensity of aggression towards large‐spotted males is likely to increase with relative abundance of C. virgo males. Thus, interspecific aggression may be an evolutionarily significant force that is able to cause divergence in secondary sexual characters.

Calopteryx splendens males exhibit a remarkable variation in wing pigmentation both within and between populations. In this study, we examined whether the wingspots of male C. splendens are related to male quality. We measured the nylon implant encapsulation rate for 85 males and found that males with larger wingspots had a faster encapsulation rate, indicating a better immunocompetence. We also found that the encapsulation rate was p ositively correlated with the density of haemocytes in the haemolymph. Another measurement of male quality, £uctuating asymmetry of wingsp ots, correlated negatively with the size of the wingspots. Males with asymmetrical wingspots also had lower encapsulation rates than more symmetrical males. Our results suggest that the size of wingspot is an indicator of male quality in C. splendens.

The immunocompetence handicap hypothesis postulates that secondary sexual traits are honest signals of mate quality because the hormones (e.g. testosterone) needed to develop secondary sexual traits have immunosuppressive effects. The best support for predictions arising from the immunocompetence handicap hypothesis so far comes from studies of insects, although they lack male-specific hormones such as testosterone. In our previous studies, we found that female mealworm beetles prefer pheromones of immunocompetent males. Here, we tested how juvenile hormone ( JH) affects male investment in secondary sexual characteristics and immune functions in the mealworm beetle, Tenebrio molitor. We injected male mealworm beetles with JH (type III) and found that injection increased the attractiveness of male pheromones but simultaneously suppressed immune functions (phenoloxidase activity and encapsulation). Our results suggest that JH, which is involved in the control of reproduction and morphogenesis, also plays a central role in the regulation of a trade-off between the immune system and sexual advertisement in insects. Thus, the results reflect a general mechanism by which the immunocompetence handicap hypothesis may work in insects.

Summary 1.Immune defence has recently been viewed as a life-history trait that shows trade-offs with other life-history traits. However, studies exploring correlations between different components of immune defence and other life-history traits are scarce. 2. In this study, two measures of immune function, body size, and development time were studied in the Mediterranean Field Cricket, Gryllus bimaculatus. 3. We found no differences between the sexes, but differences in the correlation between the measure of immune function, development time, and body size. In both sexes, encapsulation rate was negatively correlated with body size and development time, whereas lytic enzyme activity was positively correlated with these two traits. Furthermore, encapsulation rate and lytic activity were themselves negatively correlated. 4. These results indicate that there is no single trait that can be termed 'immunocompetence' and that an understanding of trade-offs between the different types of immune function and life-history traits will require a more detailed analysis of the physiological basis of the traits.