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 hormone's 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

Covid-19: Fat, Obesity, Inflammation, Ethnicity, and Sex Differences

Although obesity is known to be a risk factor for COVID-19 severity, there is an urgent need to distinguish between different kinds of fat-visceral and subcutaneous fat-and their inflammation status in COVID-19. These different fat types have partially diverging biochemical roles in the human body, and they are differentially associated with SARS-CoV-2, which targets the angiotensin-converting enzyme 2 (ACE2) for cell entry. ACE2 is highly expressed in adipose tissue, especially in visceral fat, suggesting an important role for this tissue in determining COVID-19 disease severity. In this perspective article, we discuss group differences in the amount of visceral fat levels and the extent of inflammation in adipocytes of visceral fat tissue, which may, in part, drive population, cross-national, ethnic, and sex differences in COVID-19 disease. It is vital to steer the scientific community's attention to the effects of visceral fat in creating individual and population differences in COVID-19 severity. This can help researchers unravel the reasons for the reported population, ethnic, and sex differences in COVID-19 severity and mortality

Extra-pair paternity explains cooperation in a bird species

In many social animals, females mate with multiple males, but the adaptive value of female extra-pair mating is not fully understood. Here, we tested whether male pied flycatchers (Ficedula hypoleuca) engaging in extra-pair copulations with neighboring females were more likely to assist their neighbors in antipredator defense. We found that extra-pair sires joined predator-mobbing more often, approached predators more closely, and attacked predators more aggressively than males without extra-pair offspring in the neighboring nest. Extra-pair mating may incentivize males to assist in nest defense because of the benefits that this cooperative behavior has on their total offspring production. For females, this mating strategy may help recruit more males to join in antipredator defense, offering better protection and ultimately improving reproductive success. Our results suggest a simple mechanism by which extra-pair mating can improve reproductive success in breeding birds. In summary, males siring extra-pair offspring in neighboring nests assist neighbors in antipredator defense more often than males without extra-pair offspring.publishedVersio

The obesity paradox predicts the second wave of COVID-19 to be severe in western countries

Funding Information: This work was funded by the Latvian Council of Science grants lzp-2018/1-0393 (I.A.K.), lzp-2018/2-0057 (T.K.), and lzp-2020/2-0271 (T.K.). Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.While COVID-19 infection and mortality rates are soaring in Western countries, Southeast Asian countries have successfully avoided the second wave of the SARS-CoV-2 pandemic despite high population density. We provide a biochemical hypothesis for the connection between low COVID-19 incidence, mortality rates, and high visceral adiposity in Southeast Asian populations. The SARS-CoV-2 virus uses angiotensin-converting enzyme 2 (ACE2) as a gateway into the human body. Although the highest expression levels of ACE2 are found in people’s visceral adipose tissue in Southeast Asia, this does not necessarily make them vulnerable to COVID-19. Hypothetically, high levels of visceral adiposity cause systemic inflammation, thus decreasing the ACE2 amount on the surface of both visceral adipocytes and alveolar epithelial type 2 cells in the lungs. Extra weight gained during the pandemic is expected to increase visceral adipose tissue in Southeast Asians, further decreasing the ACE2 pool. In contrast, weight gain can increase local inflammation in fat depots in Western people, leading to worse COVID-related outcomes. Because of the biological mechanisms associated with fat accumulation, inflammation, and their differential expression in Southeast Asian and Western populations, the second wave of the pandemic may be more severe in Western countries, while Southeast Asians may benefit from their higher visceral fat depots.publishersversionPeer reviewe

Body height affects the strength of immune response in young men, but not young women

Body height and other body attributes of humans may be associated with a diverse range of social outcomes such as attractiveness to potential mates. Despite evidence that each parameter plays a role in mate choice, we have little understanding of the relative role of each, and relationships between indices of physical appearance and general health. In this study we tested relationships between immune function and body height of young men and women. In men, we report a non-linear relationship between antibody response to a hepatitis-B vaccine and body height, with a positive relationship up to a height of 185 cm, but an inverse relationship in taller men. We did not find any significant relationship between body height and immune function in women. Our results demonstrate the potential of vaccination research to reveal costly traits that govern evolution of mate choice in humans and the importance of trade-offs among these traits

Effect of Juvenile Hormone on Resistance against Entomopathogenic Fungus Metarhizium robertsii Differs between Sexes

Juvenile hormone has been suggested to be a potential mediator in the trade-off between mating and insects' immunity. Studies on various insect taxons have found that juvenile hormone interferes with humoral and cellular immunity. Although this was shown experimentally, studies using highly virulent parasites or pathogens are lacking so far. In this study, we tested if juvenile hormone administration affected resistance against entomopathogenic fungi, Metarhizium robertsii, in the mealworm beetle, Tenebrio molitor. In previous studies with T. molitor, juvenile hormone has been found to reduce a major humoral immune effector-system (phenoloxidase) in both sexes and decrease the encapsulation response in males. Here, we found that juvenile hormone administration prolonged survival time after infection with M. robertsii in males but reduced survival time in females. This study indicates that the effects of juvenile hormone on insect immunity might be more complicated than previously considered. We also suggest that there might be a trade-off between specific and non-specific immunity since, in males, juvenile hormone enhances specific immunity but corrupts non-specific immunity. Our study highlights the importance of using real parasites and pathogens in immuno-ecological studies

MHC Class II Heterozygosity Associated With Attractiveness of Men and Women

The genes of the Major Histocompatibility Complex (MHC), which plays a fundamental role in the immune system, are some of the most diverse genes in vertebrates and have been connected to mate choice in several species, including humans. While studies suggest a positive relationship between MHC diversity and male facial attractiveness, the connection of MHC diversity to other visual traits and female attractiveness is still unclear. The purpose of this study was to investigate further whether MHC heterozygosity, indicating genetic quality, is associated with visual traits affecting mate preferences in humans. In total 74 Latvian men and 49 women were genotyped for several MHC loci and rated for facial and, in men, also body attractiveness. The results indicate a preference for MHC heterozygous female and male faces. However, the initially positive relationship between MHC heterozygosity and facial attractiveness becomes non-significant in females, when controlling for multiple testing, and in males, when age and fat content is taken into account, referring to the importance of adiposity in immune function and thus also attractiveness. Thus overall the effect of MHC heterozygosity on attractiveness seems weak. When considering separate loci, we show that the main gene related to facial attractiveness is the MHC class II DQB1; a gene important also in viral infections and autoimmune diseases. Indeed, in our study, heterozygous individuals are rated significantly more attractive than their homozygous counterparts, only in relation to gene DQB1. This study is the first to indicate a link between DQB1 and attractiveness in humans

MHC class II heterozygosity associated with attractiveness of men and women

The genes of the Major Histocompatibility Complex (MHC), which plays a fundamental role in the immune system, are some of the most diverse genes in vertebrates and have been connected to mate choice in several species, including humans. While studies suggest a positive relationship between MHC diversity and male facial attractiveness, the connection of MHC diversity to other visual traits and female attractiveness is still unclear. The purpose of this study was to investigate further whether MHC heterozygosity, indicating genetic quality, is associated with visual traits affecting mate preferences in humans. In total 74 Latvian men and 49 women were genotyped for several MHC loci and rated for facial and, in men, also body attractiveness. The results indicate a preference for MHC heterozygous female and male faces. However, the initially positive relationship between MHC heterozygosity and facial attractiveness becomes non-significant in females, when controlling for multiple testing, and in males, when age and fat content is taken into account, referring to the importance of adiposity in immune function and thus also attractiveness. Thus overall the effect of MHC heterozygosity on attractiveness seems weak. When considering separate loci, we show that the main gene related to facial attractiveness is the MHC class II DQB1; a gene important also in viral infections and autoimmune diseases. Indeed, in our study, heterozygous individuals are rated significantly more attractive than their homozygous counterparts, only in relation to gene DQB1. This study is the first to indicate a link between DQB1 and attractiveness in humans.Turku University Foundation, Finnish Cultural Foundation and Eesti Teadusagentuur.http://journals.sagepub.com/home/evphj2021Genetic