Parasites exert important selective pressures on host life history traits. In birds, feathers are inhabited by numerous microorganisms, some of them being able to degrade feathers or lead to infections. Preening feathers with secretions of the uropygial gland has been found to act as an antimicrobial defence mechanism, expected to regulate feather microbial communities and thus limit feather abrasion and infections. Here, we used an experimental approach to test whether Great tits (Parus major) modify their investment in the uropygial gland in response to differences in environmental microorganisms.

Microbes influence a wide range of host social behaviors and vice versa. So far, however, the mechanisms underpinning these complex interactions remain poorly understood. In social animals, where individuals share microbes and interact around foods, the gut microbiota may have considerable consequences on host social interactions by acting upon the nutritional behavior of individual animals. Here we illustrate how conceptual advances in nutritional ecology can help the study of these processes and allow the formulation of new empirically testable predictions. First, we review key evidence showing that gut microbes influence the nutrition of individual animals, through modifications of their nutritional state and feeding decisions. Next, we describe how these microbial influences and their social consequences can be studied by modelling populations of hosts and their gut microbiota into a single conceptual framework derived from nutritional geometry. Our approach raises new perspectives for the study of holobiont nutrition and will facilitate theoretical and experimental research on the role of the gut microbiota in the mechanisms and evolution of social behavior.

Parasites alter the physiology and behaviour of their hosts. In domestic honey bees, the microsporidia Nosema ceranae induces energetic stress that impairs the behaviour of foragers, potentially leading to colony collapse. Whether this parasite similarly affects wild pollinators is little understood because of the low success rates of experimental infection protocols. Here, we present a new approach for infecting bumblebees (Bombus terrestris) with controlled amounts of N. ceranae by briefly exposing individual bumblebees to parasite spores before feeding them with artificial diets. We validated our protocol by testing the effect of two spore dosages and two diets varying in their protein to carbohydrate ratio on the prevalence of the parasite (proportion of PCR-positive bumblebees), the intensity of parasites (spore count in the gut and the faeces), and the survival of bumblebees. Overall, insects fed a low-protein, high-carbohydrate diet showed the highest parasite prevalence (up to 70%) but lived the longest, suggesting that immunity and survival are maximised at different protein to carbohydrate ratios. Spore dosage did not affect parasite infection rate and host survival. The identification of experimental conditions for successfully infecting bumblebees with N. ceranae in the lab will facilitate future investigations of the sub-lethal effects of this parasite on the behaviour and cognition of wild pollinators.

To achieve sustainable targets, international panels call for a transformative change in human–nature interactions to foster human well‐being and promote pro‐environmental behaviour. The extent to which people considered themselves as part of nature—known as human–nature connectedness—has been shown to be a key societal trait for achieving such a transformative change. Human–nature connectedness is linked to improved human welfare and actions for nature conservation and can be increased by direct contact with natural environments in adults living in the Global North. It has not been shown whether these relations are true across lifetimes and in the Global South, making it difficult to generalise about the effects of human–nature connectedness globally. Here, we conducted a cross‐sectional study to examine and compare human–nature connectedness across ages in 1858 participants aged 3–87 years from two countries: France (N = 1059) and Colombia (N = 799). We also investigated the links between human–nature connectedness, pro‐environmental behaviours, well‐being and two indicators of opportunity to experience nature (i.e. degree of urbanisation and forest cover around the participants' municipality of residence). Results show that human–nature connectedness is positively related to well‐being and pro‐environmental behaviours in both countries. Analyses revealed an age‐related pattern of human–nature connectedness with a significant decline from childhood to the mid‐teens in both countries. Overall, Colombian participants have a higher human–nature connectedness than French participants and individuals' human–nature connectedness was negatively linked to the urbanisation's indices in both countries. Here, we show that human–nature connectedness is linked to sustainable outcomes in a Global South country, just as it is in the Global North. Our study also suggests that increasing contact with nature during formative teenage years could mitigate the observed decline in human–nature connectedness. Future studies are warranted combining qualitative and quantitative measures related to human–nature connectedness, nature experiences, values and practices in relation to nature, in multiple countries from the global South. Our study indicates that enhancing human–nature connectedness could provide an additional tool for achieving sustainable targets globally, not just in highly developed northern‐hemisphere countries. Read the free Plain Language Summary for this article on the Journal blog.