Development of Independence from the Mother in Gorilla gorilla gorilla

Abstract

In gorillas, the mother takes full responsibility for carrying and feeding offspring, and lactational amenorrhea prevents her from investing in another offspring while suckling. Therefore, mothers should encourage immature gorillas to become gradually more independent until they are physically able to acquire sufficient resources, travel independently, and manage social relationships unaided. We investigated the development of independence in a population of wild western gorillas (Gorilla gorilla gorilla) at Mbeli Bai, Nouabalé-Ndoki National Park, Republic of Congo. We observed the spatial proximity, the development of travel, patterns of suckling and weaning, and the nature of mother-offspring interactions for 42 immature gorillas to investigate the nature of the relationship between mother and offspring. Though mother-offspring distance and independent travel increased during immaturity, with few active interactions between the dyads, offspring still continued to suckle until a median age of 4.6 yr, longer than in mountain gorillas. The tolerance of the mother toward suckling by older offspring may reflect the importance of continued nutritional investment: the temporal nature of the diet of western gorillas means that succulent fruits-likely to be preferred weaning foodsare not always available. We propose that to buffer against potential fruit shortage, mothers continue to nurse their offspring to decrease the likelihood of death from care-dependent factors and to improve an offspring's chances of survival.

The Relationship of Accentuated Lines in Enamel to Weaning Stress in Juvenile Baboons (Papio hamadryas anubis)

“…In captive anubis baboons, mothers of male infants also experienced longer interbirth intervals Dirks /Humphrey /Dean /Jeffries than mothers of female infants, but the mother's rank was also a factor in the length of maternal investment [Garcia et al, 2009]. In both lion-tailed macaques and western lowland gorillas, male infants are suckled longer than females [Nowell and Fletcher, 2007;Krishna et al, 2008]. It is also possible that rank, age or differences in parity between the mothers of our 2 baboons account for differences in both maternal investment and the overall level of stresses in the infants [DeVore, 1963;Ransom and Rowell, 1972;Trivers, 1974;Altmann, 1980;Nicolson, 1982;Smuts and Nicolson, 1989;Lee, 1997;Johnson, 2003;Cheney et al, 2004;Altmann and Alberts, 2005;Bardi et al, 2005;Garcia et al, 2006;Johnson, 2006Johnson, , 2009, but without observational data, it is impossible to know this.…”

Lifetime reproductive success of female mountain gorillas

“…Preliminary evidence suggests a similar correlation among current gorilla populations, notwithstanding any phylogenetic inertia and/or differences in predation pressures (Nowell and Fletcher, 2007;Breuer et al, 2009;Robbins et al, 2009b). It remains unknown, however, whether demographic differences among gorilla populations reflect long term selection pressures on their life history evolution, or if they mainly arise from phenotypic plasticity in response to current ecological conditions including human disturbances (Knott, 2001;Harcourt and Stewart, 2007;Robbins et al, 2009b).…”

Using behavior to determine immature life‐stages in captive western gorillas

“…Firstly, in agreement with current immature western gorilla life history studies, adolescent males were classed as 6-8 years old [Levrero et al, 2006], and sub-adult males, termed blackbacks, from 8 years until sexually mature at 15 years old [Levrero et al, 2006;Nowell, 2005;Watts & Pusey, 1993]. Secondly, gorillas that continued to suckle from the mother [Nowell & Fletcher, 2007] were reclassified as old infants, due to their continued nutritional dependence on the mother-an observation used extensively in the literature to determine infancy [Pereira & Altmann, 1985]. Finally, the juvenile category was split into male or female individuals to illustrate any sex related differences, which were predicted to be detectable from the juvenile period in a similar way to mountain gorillas [Fletcher, 1994].…”

“…Use of an inappropriate life history classification can mask intricate species-specific differences and ultimately limits our understanding of the species' life history strategies. In the case of mountain and western gorillas, comparative research finds stark differences between the two species in terms of diet [Doran et al, 2002;Ganas et al, 2004], development [Nowell & Fletcher, 2007] and social behavior [Doran & McNeilage, 2001], regardless of being closely related. However, published research on western gorillas in captivity and in the wild [e.g.…”

“…In addition, classifications designed specifically for a species are often adopted in studies of a similar species, without understanding the life history divergence between them. For example, classifications published specifically for mountain gorillas are regularly used for western gorillas (G. gorilla gorilla) in wild and captive studies [Levrero et al, 2006;Lukas et al, 2003b;Nowell, 2005], although recent studies of western gorillas now indicate several environmental and developmental differences between the two species [Doran et al, 2002;Nowell & Fletcher, 2007].…”