Social groups buffer maternal loss in mountain gorillas

Morrison, Robin E.; Eckardt, Winnie; Colchero, Fernando; Vecellio, Veronica; Stoinski, Tara S.

doi:10.7554/elife.62939

Cited by 29 publications

(19 citation statements)

References 80 publications

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“…In gorillas, inter-birth intervals range from 4 to 6 years ( Stoinski et al, 2013 ). In male mountain gorillas, sibling bonds may last into adulthood ( Robbins, 1995 ), and following maternal loss, siblings may provide social support ( Morrison et al, 2021 ), indicating that siblings are strong partners in this species. In wild chimpanzees, inter-birth intervals range from 2 to 11 years ( Thompson, 2013 ).…”

Section: Introductionmentioning

confidence: 99%

Transition to siblinghood causes a substantial and long-lasting increase in urinary cortisol levels in wild bonobos

Behringer

Berghänel

Deschner³

et al. 2022

eLife

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In animals with slow ontogeny and long-term maternal investment, immatures are likely to experience the birth of a younger sibling before reaching maturity. In these species, the birth of a sibling marks a major event in an offspring's early life, as the older siblings experience a decrease in maternal support. The transition to siblinghood (TTS) is often considered to be stressful for the older offspring, but physiological evidence is lacking. To explore the TTS in wild bonobos, we investigated physiological changes in urinary cortisol (stress response), neopterin (cell-mediated immunity), and total triiodothyronine (T3, metabolic rate), as well as changes in behaviors that reflect the mother-offspring relationship. Following a sibling's birth, urinary cortisol levels of the older offspring increased fivefold, independent of their age, and remained elevated for seven months. The cortisol level increase was associated with declining neopterin levels, however T3 levels and behavioral measures did not change. Our results indicate that the TTS is accompanied by elevated cortisol levels and that this change does not coincide with nutritional weaning and attainment of physical independence. Our results suggest that bonobos and humans experience TTS in similar ways and that this developmental event may have emerged in the last common ancestor.

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Section: Introductionmentioning

confidence: 99%

Transition to siblinghood causes a substantial and long-lasting increase in urinary cortisol levels in wild bonobos

Behringer

Berghänel

Deschner³

et al. 2022

eLife

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“…First, gorilla social groups are tight-knit and cohesive compared to their close ape relatives ( Goodall, 1986 ; Remis, 1997 ; Morrison et al, 2021b ; Schaller and Emlen, 1963 ; Doran and McNeilage, 1998 ), reflected by remarkable features such as the ability for these groups to buffer the fitness costs of maternal loss ( Morrison et al, 2021a ). Due to this highly cohesive structure, all individuals in a group, related or not, are very likely quite familiar with one another.…”

Section: Discussionmentioning

confidence: 99%

“…A mismatch between historical and current social structure might also lead to inconsistent, weakened kin recognition among paternal siblings that manifests in the contrasting patterns we report. Ultimately, disentangling these potential explanations within a species that only exists in the wild may depend on the opportunity to study long-term mating patterns and the impacts of ‘natural experiments’ such as early maternal loss or adoption (most often carried out by adult males in this species; Fossey, 1979 ; Morrison et al, 2021a ).…”

Section: Discussionmentioning

confidence: 99%

Mountain gorillas maintain strong affiliative biases for maternal siblings despite high male reproductive skew and extensive exposure to paternal kin

Grebe

Hirwa

Stoinski

et al. 2022

eLife

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Evolutionary theories predict that sibling relationships will reflect a complex balance of cooperative and competitive dynamics. In most mammals, dispersal and death patterns mean that sibling relationships occur in a relatively narrow window during development, and/or only with same-sex individuals. Besides humans, one notable exception are mountain gorillas, in which non-sex biased dispersal, relatively stable group composition, and the long reproductive tenures of alpha males mean that animals routinely reside with both maternally and paternally related siblings, of the same and opposite sex, throughout their lives. Using nearly 40,000 hours of behavioral data collected over 14 years on 699 sibling and 1235 non-sibling pairs of wild mountain gorillas, we demonstrate that individuals have strong affiliative preferences for full and maternal siblings over paternal siblings or unrelated animals, consistent with an inability to discriminate paternal kin. Intriguingly, however, aggression data imply the opposite. Aggression rates were statistically indistinguishable among all types of dyads except one: in mixed-sex dyads, non-siblings engaged in substantially more aggression than siblings of any type. This pattern suggests mountain gorillas may be capable of distinguishing paternal kin, but nonetheless choose not to affiliate with them over non-kin. We observe a preference for maternal kin in a species with high reproductive skew (i.e., high relatedness certainty), even though low reproductive skew (i.e., low relatedness certainty) is believed to underlie such biases in other non-human primates. Our results call into question reasons for strong maternal kin biases when paternal kin are identifiable, familiar, and similarly likely to be long-term groupmates, and they may also suggest behavioral mismatches at play during a transitional period in mountain gorilla society.

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“…We recommend similar studies of potential orphan stunting within other long-term projects of terrestrial mammals. Research into possible stunting would be especially interesting in a species in which adoption is common such as the mountain gorilla ( Morrison et al , 2021 ), or with a l arger sample size of adopted individuals in chimpanzees as suggested by Samuni et al (2020) . Adopted orphans may grow at the same rate as non-orphans, or at least show less stunting than unadopted orphans.…”

Section: Discussionmentioning

confidence: 99%

Orphaning stunts growth in wild African elephants

Parker

Wittemyer

2022

Conservation Physiology

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Orphans of several species suffer social and physiological consequences such as receiving more aggression from conspecifics and lower survival. One physiological consequence of orphaning, stunted growth, has been identified in both humans and chimpanzees, but has not been assessed in a non-primate species. Here, we tested whether wild African elephant orphans show evidence of stunted growth. We measured individually known female elephants in the Samburu and Buffalo Springs National Reserves of Kenya, with a rangefinder capable of calculating height, to estimate a von Bertalanffy growth curve for female elephants of the study population. We then compared measurements of known orphans and non-orphans of various ages, using a Bayesian analysis to assess variation around the derived growth curve. We found that orphans are shorter for their age than non-orphans. However, results suggest orphans may partially compensate for stunting through later growth, as orphans who had spent a longer time without their mother had heights more similar to non-orphans. More age mates in an individual’s family were associated with taller height, suggesting social support from peers may contribute to increased growth. Conversely, more adult females in an individual’s family were associated with shorter height, suggesting within-group competition for resources with older individuals may reduce juvenile growth. Finally, we found a counterintuitive result that less rainfall in the first 6 years of life was correlated with taller height, potentially reflecting the unavoidable bias of measuring individuals who were fit enough to survive conditions of low rainfall as young calves. Reduced growth of individuals has been shown to reduce survival and reproduction in other species. As such, stunting in wildlife orphans may negatively affect fitness and represents an indirect effect of ivory poaching on African elephants.

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Social groups buffer maternal loss in mountain gorillas

Cited by 29 publications

References 80 publications

Transition to siblinghood causes a substantial and long-lasting increase in urinary cortisol levels in wild bonobos

Transition to siblinghood causes a substantial and long-lasting increase in urinary cortisol levels in wild bonobos

Mountain gorillas maintain strong affiliative biases for maternal siblings despite high male reproductive skew and extensive exposure to paternal kin

Orphaning stunts growth in wild African elephants

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