Willaume, E. | Search bioRxiv

bioRxiv2025

Hidden hematological, biochemical and immune costs of asymptomatic malaria infections in semi-wild chimpanzees

The health consequences of Plasmodium infections in wild great apes, particularly in asymptomatic animals, remain poorly understood. This study investigated the hematological and immune impacts of natural malaria infections in 27 semi-wild chimpanzees (Pan troglodytes troglodytes) from Gabon. Using MinION sequencing and species-specific PCR, results showed a 48.15% overall Plasmodium infection rate, with frequent multi-species co-infections involving Plasmodium gaboni, Plasmodium reichenowi, and Plasmodium vivax-like parasites. In addition, younger animals were significantly more infected and exhibited higher parasitemia levels, especially those with triple infections involving P. vivax-like. Profiling of 15 hematological markers and 8 cytokines/chemokines known to be associated with malarial infections in humans revealed significant alterations in infected chimpanzees, including elevated urea, reduced creatinine, and increased systemic concentrations of pro-inflammatory (TNF, IL-1{beta}, CCL3) and anti-inflammatory (IL-10) cytokines. Ex vivo PBMC stimulation yielded higher IL-10 in infected than non-infected individuals, indicating a regulatory-skewed cytokine response at the time of sampling. These results suggest that malaria in chimpanzees is associated with systemic immune modulation and accompanied by signs of physiological stress, including potential renal dysfunction. This study challenges the assumption that chronic Plasmodium infections are entirely benign in great apes and highlight the need to integrate immunological health indicators into conservation strategies. Broader immune profiling and longitudinal studies will be essential in the future to assess long-term health outcomes and resilience in these endangered populations.

evolutionary biology↗

bioRxiv2022

Primate mothers promote proximity between their offspring and infants who look like them

Behavioral discrimination of kin is a key process structuring social relationships in animals. In this study, we provide a first example of discrimination towards non-kin by third-parties through a mechanism of phenotype matching. In mandrills, we recently demonstrated increased facial resemblance among paternally-related juvenile and adult females indicating adaptive opportunities for paternal kin recognition. Here, we hypothesize that mothers use offsprings facial resemblance with other infants to guide offsprings social opportunities towards similarly-looking ones. Using deep learning for face recognition in 80 wild mandrill infants, we first show that infants born to the same father or conceived during the tenure of the same alpha male resemble each other the most, independently of their age, sex or maternal origin, extending previous results to the youngest age class. Using long-term behavioral observations on association patterns and controlling for matrilineal origin, maternal relatedness and infant age and sex, we then demonstrate that, as hypothesized, mothers are spatially closer to infants that resemble their own offspring more, thereby facilitating associations among similar-looking infants. Using theoretical modeling, we describe a plausible evolutionary process whereby mothers gain fitness benefits by promoting nepotism among paternally related infants. This mechanism, that we call "second-order kin selection", may extend beyond mother-infant interactions and has the potential to explain cooperative behaviors among non-kin in social species, including humans.

evolutionary biology↗