The behavioral immune system in grey mouse lemurs: Causes of individual variation in behavioral defenses and consequences for socio-ecological traits

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Parasite-mediated selection has driven the emergence of host defense mechanisms to limit the spread of parasites. In addition to the physiological immune system (‘ΨIS’), animals have developed a “behavioral immune system” (‘βIS’), which comprises a sophisticated set of anti-parasitic strategies, such as avoidance of contaminated substrates or infected conspecifics. Individuals vary in their degree of investment in behavioral defenses, which may contribute to heterogeneity in parasite distribution within populations and have far-reaching consequences for socio-ecological traits of species. To maximize their fitness, animals should balance investment between ΨIS and βIS because both systems incur energetic costs. However, the determinants underlying variation in anti-parasitic behavior remain poorly understood and few studies have investigated interactions between expression of βIS and ΨIS. To contribute to this emerging research field, I propose to investigate anti-parasitic behaviors in grey mouse lemurs (Microcebus murinus). This nocturnal Malagasy primate exhibits a rare form of facultative sociality: some animals form day-time sleeping associations while others sleep alone. Preliminary work revealed that this species exhibits several anti-parasitic behaviors and that individuals show variation in parasite avoidance. In a first part, using behavioral tests conducted on both captive and wild animals, I will investigate causes of inter-individual variation in parasite avoidance behaviors. In particular, I will test (1) whether group-living individuals invest more in behavioral defenses than their solitary counterparts to cope with parasite-mediated costs of sociality, and (2) whether behavioral defenses may compensate for poor or temporarily compromised individual immuno-competence. In a second part, combining a correlative and an experimental approach, I will investigate the influence of these avoidance behaviors on several aspects of their sleeping ecology. In particular, I will test (1) whether nest parasite contamination influences sleeping site usage patterns and (2) whether individual parasite status influences sleeping associations. This project has the potential to shed light on the crucial role played by the βIS in the co-evolutionary dynamics between hosts and their parasites.