Unconditional care from close maternal kin in the face of parasites

Abstract

Several species mitigate relationships according to their conspecifics' parasite status. Yet, this defence strategy comes with the costs of depriving individuals from valuable social bonds. Animals therefore face a trade-off between the costs of pathogen exposure and the benefits of social relationships. According to the models of social evolution, social bonds are highly kin-biased. However, whether kinship mitigates social avoidance of contagious individuals has never been tested so far. Here, we build on previous research to demonstrate that mandrills ( Mandrillus sphinx ) modulate social avoidance of contagious individuals according to kinship: individuals do not avoid grooming their close maternal kin when contagious (parasitized with oro-faecally transmitted protozoa), although they do for more distant or non-kin. While individuals' parasite status has seldom been considered as a trait impacting social relationships in animals, this study goes a step beyond by showing that kinship balances the effect of health status on social behaviour in a non-human primate.

Sickness effects on social interactions depend on the type of behaviour and relationship

“…Given this extensive maternal investment (Carter, Wilkinson, & Page, 2017; Delpietro & Russo, 2002) and the fact that a mother is often the primary food donor for each female bat (Carter & Wilkinson, 2013; Wilkinson, 1984), it is likely that reducing maternal care is more costly to fitness than the physiological risks posed interacting with an infected bat (Lopes, 2014). Several other experiments also suggest that the need for maternal care can partially overcome sickness behaviour (Aubert, Goodall, Dantzer, & Gheusi, 1997; Weil, Bowers, Dow, & Nelson, 2006) or pathogen avoidance (Poirotte & Charpentier, 2020). Transmission probabilities based on interaction rates could remain unchanged between a sick mother and her offspring but decrease between the same bat and non‐closely related groupmates (Figure 2).…”

Behavioral Immune Trade-Offs: Interpersonal Value Relaxes Social Pathogen Avoidance

“…A well-designed behavioral immune system should instead balance the costs of pathogen exposure against those of social avoidance in a target-specific manner. Guided by the considerations described above, researchers have uncovered evidence that mandrills groom parasitized maternal kin but avoid grooming other parasitized conspecifics (Poirotte & Charpentier, 2020) and that human mothers report less disgust toward their own baby’s diapers than other babies’ diapers (Case et al, 2006).…”

Strangers look sicker (with implications in times of COVID‐19)

“…Mandrills abstain from grooming contagious mates unless these are close maternal kin (mother, offspring, maternal half‐siblings) and it has been suggested they might be less sensitive to infection cues associated with kin. [ 69 ] Note, however, that they treat infected paternal half‐siblings exactly as they treat infected distant kin or nonkin, even though paternal half‐siblings are every bit as related to them as are maternal ones, and can be recognized as kin. [ 70 ] Yet of course maternal half‐siblings are exposed to one another a great deal because they are raised together from birth, whilst paternal half‐siblings grow up in entirely different families.…”