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Energy investment in reproduction is predicted to trade off against other necessary physiological functions like immunity, but it is unclear to what extent this impacts fitness in long-lived species. Among mammals, female primates, and especially apes, exhibit extensive periods of investment in each offspring. During this time, energy diverted to gestation and lactation is hypothesized to incur short and long-term deficits in maternal immunity and lead to accelerated ageing. We examined the relationship between reproduction and immunity, as measured by faecal parasite counts, in wild female chimpanzees ( Pan troglodytes schweinfurthii ) of Kibale National Park, Uganda. While we observed higher parasite shedding (counts of eggs, cysts and larvae) in pregnant chimpanzees relative to cycling females, parasites rapidly decreased during early lactation, the most energetically taxing phase of the reproductive cycle. Additionally, while our results indicate that parasite shedding increases with age, females with higher fertility for their age had lower faecal parasite counts. Such findings support the hypothesis that the relatively conservative rate of female reproduction in chimpanzees may be protective against the negative effects of reproductive effort on health. This article is part of the theme issue ‘Evolution of the primate ageing process’.

“Village dogs” in developing economies are assumed to be heavily burdened by infectious disease. We followed a cohort of 61 village dogs in rural western Uganda prospectively for fifteen months to measure changes in health and demographic outcomes, and to examine risk factors for morbidity and mortality. The mean (± standard deviation) number of dogs per household was 2.4 (± 2.0), of which 56.0% were male and 44.0% female. For females, average age at first estrus was 1.7 (± 0.6) years with a mean litter size of 3.8 (± 1.5). In the first, second and third parities, average puppy mortality per litter was 3.2 (± 2.5), 2.4 (± 2.1) and 3.4 (± 2.9), respectively. The main causes of morbidity and mortality were infectious disease (46.1%), culling (euthanasia) by owners (30.8%), and attacks by baboons, Papio anubis (23.1%). Cox proportional hazard regression showed that a clinical diagnosis of anemia significantly predicted morbidity (HR = 4.3 (95% CI: 1.1–17.8); p < 0.05), and younger age significantly predicted mortality (HR = 3.6 (95% CI: 1.2–10.6); p < 0.05). Our results indicate that infectious disease is indeed important to the health and survival in village dogs in this setting, but that cultural practices related to ownership and interactions with wildlife also contribute substantially to morbidity and mortality.

Hunting and consumption of wild animals, colloquially known as “bushmeat,” is associated with health trade-offs. Contact with wildlife increases exposure to wildlife-origin zoonotic diseases yet bushmeat is an important nutritional resource in many rural communities. In this study, we test the hypothesis that bushmeat improves food security in communities that hunt and trade bushmeat regularly. We conducted 478 interviews with men and women in six communities near Cross River National Park in Nigeria. We used interview responses to relate prevalence and diversity of bushmeat consumption to household food security status. Animal-based foods were the most commonly obtained items from the forest, and 48 types of wild vertebrate animals were consumed within the past 30 days. Seventy-five percent of households experienced some degree of food insecurity related to food access. Bushmeat consumption was significantly associated with relatively higher household food security status. Rodents were more important predictors of food security than other animal taxa. Despite increased bushmeat consumption in food-secure households, food-insecure households consumed a higher diversity of bushmeat species. Results show that consumption of bushmeat, especially rodents, is uniquely related to improved food security. Reliance on a wider diversity of species in food-insecure households may in turn affect their nutrition, exposures to reservoirs of zoonotic infections, and impact on wildlife conservation. Our results indicate that food security should be addressed in conservation and public health strategies aimed at reducing human–wildlife contact, and that improved wildlife protection, when combined with alternative animal-based foods, would positively affect food security in the long term.

Parasites are ubiquitous in wildlife populations, but physiological and behavioural responses of hosts to infection are difficult to measure. We experimentally treated semi-free-ranging red-capped mangabeys ( Cercocebus torquatus ) in Nigeria with antiparasitic drugs and examined subsequent changes in glucocorticoid production and individual behaviour. Because both parasites and stress impact energy balance and health, we measured (i) behavioural time re-allocation via activity budgets, (ii) social relationships (e.g. social connectivity and dominance hierarchy stability) and (iii) body condition. We collected triplicate faecal samples ( n = 441) from 49 individuals prior to and following treatment. Cortisol levels fluctuated in parallel with parasite abundance. Elevations in cortisol, but not parasitism, were related to reduced body condition. Behaviour also shifted according to infection status, with uninfected individuals spending more time foraging and less time resting and vigilant compared with when they were infected. Time spent feeding, travelling or socializing did not differ between pre- and post-treatment time periods. Group cohesion, but not dominance stability, changed following treatment, suggesting parasite-induced social avoidance. Together, these findings show a coordinated response to infection that promotes host tolerance through stress and energy conservation, reduces transmission risk and increases protection when infected hosts are vulnerable.

Shoes are effective for blocking soil-transmitted helminths (STHs) that penetrate the skin. Unfortunately, shoe-wearing is uncommon in many areas where STHs are prevalent, in part because local populations are unaware of the health benefits of wearing shoes. This is especially true in low-literacy populations, where information dissemination through written messages is not possible. We launched a public health intervention that combines a public health image with sandals. The image is a "lenticular image" that combines two alternating pictures to depict the efficacy of shoes for preventing STH infection. This image is adhered to the shoe, such that the message is linked directly to the primary means of prevention. To create a culturally appropriate image, we conducted five focus group discussions, each with a different gender and age combination. Results of focus group discussions reinforced the importance of refining public health messages well in advance of distribution so that cultural acceptability is strong. After the image was finalized, we deployed shoes with the image in communities in western Uganda where hookworm is prevalent. We found that the frequency of shoe-wearing was 25% higher in communities receiving the shoes than in control communities. Microscopic analyses of fecal samples for parasites showed a sustained reduction in infection intensity for parasites transmitted directly through the feet when people received shoes with a public health image. Our results show that combining culturally appropriate images with public health interventions can be effective in low-literacy populations.

What types of cues do callitrichid primates use to detect and respond to predators? Do they respond to predator-specific cues or to more general cues? The evidence for these questions remains conflicting. We presented captive-born and reared cotton-top tamarins with no previous exposure to predators (or predator cues) with vocalizations from three potential predators of cotton-top tamarin in the wild (white hawk, jaguar, and tayra) and with vocalizations from sympatric nonpredators (black-faced antthrush and red howler monkey). Vocalizations from predators and from nonpredator mammals elicited equivalent arousal, fear, and vocal responses. Howler monkey roars produced the strongest responses. The results suggest that predator-naïve cotton-top tamarins do not recognize specific predator vocalizations, but may respond to vocal qualities (low-frequency, noisy sounds) that indicate large body size, threat, or aggression. On the other hand, tamarins responded much more strongly to the higher frequency calls from the hawk than the antthrush, suggesting another mechanism must also be involved. The failure of captive-reared tamarins to distinguish between vocalizations of predators and nonpredator mammals has important implications for reintroduction studies.

Substantial research has shown that while some parasite infections can be fatal to hosts, most infections are sub-clinical and non-lethal. Such sub-clinical infections can nonetheless have negative consequences for the long-term fitness of the host such as reducing juvenile growth and the host's ability to compete for food and mates. With such effects, infected individuals are expected to exhibit behavioural changes. Here we use a parasite removal experiment to quantify how gastrointestinal parasite infections affect the behaviour of vervet monkeys (Chlorocebus aethiops) at Lake Nabugabo, Uganda. Behavioural profiles and the structure of nearest neighbour relationships varied significantly. As predicted, after deworming the duration of the resting events decreased, which is consistent with the idea that parasite infections are energetically costly. In contrast to what was predicted, we could not reject the null hypothesis and we observed no change in either the frequency or duration of grooming, but we found that the duration of travel events increased. A network analysis revealed that after deworming, individuals tended to have more nearest neighbours and hence probably more frequent interactions, with this effect being particularly marked for juveniles. The heightened response by juveniles may indicate that they are avoiding infected individuals more than other age classes because it is too costly to move energy away from growth. We consider that populations with high parasite burden may have difficulties developing social networks and behaviours that could have cascading effects that impact the population in general.