Sex differences in disease avoidance behavior vary across modes of pathogen exposure

Sex differences in disease susceptibility are widespread, and these disparities are often compounded in cases where sexual dimorphism increases exposure risk to parasites for one sex more than the other. Studies rarely link sex differences in disease susceptibility to sex differences in infection avoidance behavior. Yet, understanding the intersection of hosts’ susceptibility to infection and infection avoidance behavior is essential to predicting infection risk variation. Here, we use the fruit fly Drosophila melanogaster and a generalist entomopathogenic fungus, Metarhizium robertsii, which can be transmitted directly, indirectly, and post-mortem as a model host–pathogen system. We test whether the relationship between susceptibility to infection and pathogen avoidance behavior covaries with host sex. We first measured differences in resistance between male and female flies after three different types of exposure—direct, sexual, and environmental—to infectious fungal conidiospores. Then, we tested whether male and female flies differed in the likelihood of mating with infected partners and their avoidance of food patches with increased infection risk. Females were more susceptible to infection under all three exposure techniques. When confronted with an infectious partner, females mated sooner than males. However, when given a choice between an exposed partner and an unexposed partner, females take longer to begin copulating compared with males, though neither sex was more likely to choose the unexposed partner than expected by chance. Neither male nor females flies avoided food patches containing infectious conidiospores, though only females show an aversion to food sites containing an infectious fly corpse. These experiments suggest that sex differences in disease susceptibility may be counteracted via differential pathogen avoidance behavior, though the strength of avoidance behavior appears to vary across different contexts of infection risk.     

Anticipated effects of abiotic environmental change on intraspecific social interactions

Social interactions are ubiquitous across the animal kingdom. A variety of ecological and evolutionary processes are dependent on social interactions, such as movement, disease spread, information transmission, and density-dependent reproduction and survival. Social interactions, like any behaviour, are context dependent, varying with environmental conditions. Currently, environments are changing rapidly across multiple dimensions, becoming warmer and more variable, while habitats are increasingly fragmented and contaminated with pollutants. Social interactions are expected to change in response to these stressors and to continue to change into the future. However, a comprehensive understanding of the form and magnitude of the effects of these environmental changes on social interactions is currently lacking. Focusing on four major forms of rapid environmental change currently occurring, we review how these changing environmental gradients are expected to have immediate effects on social interactions such as communication, agonistic behaviours, and group formation, which will thereby induce changes in social organisation including mating systems, dominance hierarchies, and collective behaviour. Our review covers intraspecific variation in social interactions across environments, including studies in both the wild and in laboratory settings, and across a range of taxa. The expected responses of social behaviour to environmental change are diverse, but we identify several general themes. First, very dry, variable, fragmented, or polluted environments are likely to destabilise existing social systems. This occurs as these conditions limit the energy available for complex social interactions and affect dissimilar phenotypes differently. Second, a given environmental change can lead to opposite responses in social behaviour, and the direction of the response often hinges on the natural history of the organism in question. Third, our review highlights the fact that changes in environmental factors are not occurring in isolation: multiple factors are changing simultaneously, which may have antagonistic or synergistic effects, and more work should be done to understand these combined effects. We close by identifying methodological and analytical techniques that might help to study the response of social interactions to changing environments, highlight consistent patterns among taxa, and predict subsequent evolutionary change. We expect that the changes in social interactions that we document here will have consequences for individuals, groups, and for the ecology and evolution of populations, and therefore warrant a central place in the study of animal populations, particularly in an era of rapid environmental change.