Disease avoidance, and breeding group age and size condition the dispersal patterns of western lowland gorilla females

Abstract

Social dispersal is an important feature of population dynamics. When female mammals occur in polygynous groups, their dispersal decisions are conditioned by various female‐, male‐, and group‐related factors. Among them, the influence of disease often remains difficult to assess. To address this challenge, we used long‐term monitoring data from two gorilla populations (Gorilla gorilla gorilla) affected by infectious skin disease lesions. After controlling for other potentially influential factors, we investigated to which extent disease avoidance drives the dispersal decisions of gorilla females. We showed that the infection of a silverback of a breeding group by the skin disease increased the probability of adult females to emigrate. Moreover, adult females avoided breeding groups with a high prevalence of skin disease by emigrating from them and immigrating into healthier ones. Age of the breeding group was also an important factor. Adult females left older groups, near the end of a male tenure, to join younger ones led by younger fully grown silverbacks that could be of high reproductive and protective value. Our study highlights that, although females select for high‐quality males, disease avoidance is a critical driver of their dispersion decision.

Bidirectional interactions between host social behaviour and parasites arise through ecological and evolutionary processes

“…In contrast, honey bee colonies were more likely to accept entry by foreign bees infected with Israeli acute paralysis virus than foreign controls, which may represent a unique case of pathogen manipulation of chemical signals that mediate aggressive interactions in this species [Geffre et al, 2020; see 'Host social behaviours influence parasite evolution (Arrow D)' section]. The movement or dispersal of uninfected individuals between groups can also be driven by conspecific infection or disease status, as occurs in western lowland gorillas (Gorilla gorilla gorilla), where adult females are more likely to emigrate from social groups with a higher prevalence of facial lesions associated with a contact-transmitted skin disease (Baudouin et al, 2019). Overall, more studies are needed on how parasite infection influences among-group movements for both infected hosts and uninfected conspecifics, particularly for taxa where social group composition is relatively fluid, such as fission-fusion societies.…”

Inbreeding and disease avoidance in a free‐ranging koala population

“…Some species are known to actively avoid diseased conspecifics, such as the spiny lobster ( Panulirus argus ) which avoids sharing shelters with diseased conspecific (Behringer & Butler, 2010; Behringer, Butler, & Shields, 2006), while bullfrog tadpoles ( Rana catesbeiana ) avoid proximity to tadpoles infected with a yeast infection (Kiesecker, Skelly, Beard, & Preisser, 1999). Moreover, the presence of infectious skin lesions in silverback gorillas ( Gorilla gorilla gorilla ) increases the likelihood of females emigrating from the breeding group (Baudouin et al., 2019).…”

No evidence for female kin association, indications for extragroup paternity, and sex‐biased dispersal patterns in wild western gorillas

“…The genetic analysis also provided insights on group age. Most immatures for which Cervus could reliably identify the father but not the mother were in the same group, RC2, which suggests that their mothers may have already left the group, and females have been found to leave older or weaker males to join younger (fitter) males (Baudouin et al., 2019; Manguette, Robbins et al., 2020). Indeed, the RC2 group composition (with very few adult females and quite a few older offspring) was in agreement with that of previously described old groups (Parnell, 2002).…”

“…Moreover, it improves reproductive success by limiting intragroup feeding competition. Therefore, western gorilla females seem to show unconditionally a strategy of natal dispersal by departing from the group in which they were born (Baudouin et al., 2019; Manguette, Robbins et al., 2020; Stokes et al., 2003).…”

“…Breeding groups of western gorillas ( G. gorilla ) typically include one silverback (Breuer et al., 2010; Gatti et al., 2004; Parnell, 2002), while in eastern gorillas ( G. beringei ), for the well‐studied mountain gorilla, multiple males frequently coexist in a single group (40% of the groups), even though a dominant silverback sires most of the offspring (Bradley et al., 2005). The twice more frequent secondary female dispersal found in western versus eastern gorillas might thus be explained by the greater need of western gorilla females to increase mate choice and reproductive success (Baudouin et al., 2019; Manguette, Robbins et al., 2020; Stokes et al., 2003).…”