Silverback Male Presence and Group Stability in Gorillas (Gorilla gorilla gorilla)

Margulis, Susan W.; Whitham, Jessica C.; Ogorzalek, Kevin

doi:10.1159/000070004

Cited by 3 publications

(3 citation statements)

References 6 publications

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“…We preferentially use the latter here, because there are phenotypic changes associated with advancing age, such as greying of the hair in many mammals, which might not in themselves impair performance in any way. Indeed, in some species of primates such as the gorilla ( Gorilla gorilla gorilla ), such greying is associated with an increase in performance, when so-called 'silver backs' gain mating or resource acquisition advantages (Margulis, Whitham & Ogorzalek 2003). Are these apparently trivial phenotypic changes, albeit age-related, not in fact 'senescent' or are they harbingers, or side effects, of deterioration at other levels in the body?…”

Section: What Is Senescence?mentioning

confidence: 99%

The evolutionary ecology of senescence

Monaghan¹,

Charmantier²,

Nussey³

et al. 2008

Functional Ecology

298

309

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Summary 1.Research on senescence has largely focused on its underlying causes, and is concentrated on humans and relatively few model organisms in laboratory conditions. To understand the evolutionary ecology of senescence, research on a broader taxonomic range is needed, incorporating field, and, where possible, longitudinal studies. 2. Senescence is generally considered to involve progressive deterioration in performance, and it is important to distinguish this from other age-related phenotypic changes. We outline and discuss the main explanations of why selection has not eliminated senescence, and summarise the principal mechanisms thought to be involved. 3. The main focus of research on senescence is on age-related changes in mortality risk. However, evolutionary biologists focus on fitness, of which survival is only one component. To understand the selective pressures shaping senescence patterns, more attention needs to be devoted to age-related changes in fecundity. 4. Both genetic and environmental factors influence the rate of senescence. However, a much clearer distinction needs to be drawn between life span and senescence rate, and between factors that alter the overall risk of death, and factors that alter the rate of senescence. This is particularly important when considering the potential reversibility and plasticity of senescence, and environmental effects, such as circumstances early in life. 5. There is a need to reconcile the different approaches to studying senescence, and to integrate theories to explain the evolution of senescence with other evolutionary theories such as sexual and kin selection.Key-words: ageing, antagonistic pleiotropy, disposable soma, evolution, lifespan, mortality, mutation accumulation, oxidative stress Organisms change during their lifetimes in many ways, sometimes permanently as with most aspects of body growth and development, but sometimes temporarily, as with seasonal leaf loss and replacement, growth and regression of gonads, pre-migratory and pre-hibernation accumulation of fat reserves, or development of thicker fur or down in response to decreases in temperature. The predictability and reversibility of such change is of great interest to biologists, and we seek to understand how change is controlled and what fitness advantages it confers. Changes that occur in old age, generally referred to as ageing or senescence, are particularly fascinating, since these progressive and irreversible changes impair rather than improve performance, with apparently negative effects on fitness. Understanding the evolution and persistence of senescence therefore poses a particular challenge.The typical route followed in biological research is to observe a natural process and then try to understand and explain it by investigations under controlled conditions, often in the laboratory. In this respect, research on senescence has followed an unusual path since, in many animal taxa, it was first studied in captive or laboratory conditions. The subsequent emphasis on the mechanisms resp...

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Section: What Is Senescence?mentioning

confidence: 99%

The evolutionary ecology of senescence

Monaghan¹,

Charmantier²,

Nussey³

et al. 2008

Functional Ecology

298

309

View full text Add to dashboard Cite

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“…In both free-ranging and captive settings, the silverback in all species of gorillas provides protection and leadership, mediating conflict within a group [Hoff et al, 1982[Hoff et al, , 1998Watts, 1991] and facilitating group stability [Margulis et al, 2003]. After the death of a silverback in a single-adult-male group in the wild, western lowland female gorillas will disperse and eventually transfer to another group or to a solitary male [Parnell, 2002].…”

Section: Introductionmentioning

confidence: 99%

Behavioral response of captive western lowland gorillas (Gorilla gorilla gorilla) to the death of silverbacks in multi‐male groups

et al. 2009

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In both free-ranging and captive western lowland gorillas, a silverback provides protection and leadership, mediating conflict within a group. In the wild, when a dominant silverback dies the group will disperse or transfer to a solitary male, unless a subsequent male is present to inherit the group. In captivity, studies have focused on groups containing one male and therefore it is unclear how gorillas respond to the death or removal of a silverback in multi-male groups. This study examined the behavior of a bachelor group (Cleveland Metroparks Zoo) and a multi-male, mixed-sex group (Pittsburgh Zoo and PPG Aquarium) following the death of two older silverbacks in 2005. Both of the younger but dominant males maintained their same level of dominance after the death. We predicted that agonism would increase after the death as groups struggled for social stablility. We did observe an increase in both agonism and displacements among the bachelor group, but only observed an increase in displacements among the mixed-sex group. Although we predicted that there would be no change in solitary behavior, both groups decreased feeding and the mixed-sex group increased self-directed behavior post-death. In the bachelor group, self-directed behavior decreased and undesirable behavior increased. We also observed a difference in spatial distance after the death with members of the mixed-sex group becoming more dispersed and members of the bachelor group more converged. This study demonstrates that there is a period of transition for multi-male groups after the death or removal of the oldest silverback. Future research could integrate physiological measures with behavioral analyses before and after the death or removal of a prominent member of the group.

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“…The gorilla is the primate exemplar of polygamy, carrying many markers of overt, somatic mating competition. With groups of around eight (Parnell, 2002) often containing a single breeding male (Margulis, Whitham, & Ogorzalek, 2003), reproductive success pivots on the ability to obtain and maintain a harem (Breuer et al, 2010). Massive heads with prominent fatty ridges and resonating air pockets that undergird the oft-beat chest may be unique markers of polygamy among gorillas (Breuer, Robbins, & Boesch, 2007); although, in addition to such stylized symbols, gorillas possess the sexually dimorphic pelage variation, which signals intra-male polygamous conflict (Plavcan, 2001).…”

Section: Gorilla Gorilla: the Signature Of Polygamymentioning

confidence: 99%

Toward a Biology of Collectivism

Hertler

2015

Sage Open

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The signs of mating competition are written into the physiology of the human male, but they are not written equally into the physiology of all racial groupings of human males. It seems that Asian males are different, different in that they are more fully dissimilar from the gorilla than are other races, showing less sexual dimorphism, muscularity, and less marked secondary sexual characteristics, and different in that they are more fully dissimilar from the chimpanzee than are other races, showing less sexual drive and activity as well as smaller testicles and lower sperm counts. It is presently argued that such anatomical differences are a testament to a more peaceably monogamous mating history. In turn, it is then argued that such physiological markers are directly associated with the collectivist ethos that has been historically, anthropologically, and sociologically observed among the Asian people.

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Silverback Male Presence and Group Stability in Gorillas (Gorilla gorilla gorilla)

Cited by 3 publications

References 6 publications

The evolutionary ecology of senescence

The evolutionary ecology of senescence

Behavioral response of captive western lowland gorillas (Gorilla gorilla gorilla) to the death of silverbacks in multi‐male groups

Toward a Biology of Collectivism

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