Variability in the developmental life history of the genusGorilla

Abstract

Life history is influenced by factors both intrinsic (e.g., body and relative brain size) and extrinsic (e.g., diet, environmental instability) to organisms. In this study, we examine the prediction that energetic risk influences the life history of gorillas. Recent comparisons suggest that the more frugivorous western lowland gorilla shows increased infant dependence, and thus a slower life history, than the primarily folivorous mountain gorilla to buffer against the risk of starvation during periods of food unpredictability. We further tested this hypothesis by incorporating additional life history data from wild western lowland gorillas and captive western lowland gorillas with the assumption that the latter live under ecological conditions of energetic risk that more closely resemble those of mountain gorillas and thus should show faster life histories than wild members of the species. Overall, we found captive western lowland and wild mountain gorillas to have faster developmental life histories than wild western lowland gorillas, weaning their infants approximately a year earlier and thus reducing interbirth intervals by a year. These results provide support that energetic risk plays an important role in determining gorilla life history. Unlike previous assertions, gorillas do not have substantially faster life histories, at least at the genus level, than other great apes. This calls for a re-evaluation of theories concerning comparative ape life history and evolution and highlights the need for data from additional populations that vary in energetic risk.

Niche Partitioning in Sympatric Gorilla and Pan from Cameroon: Implications for Life History Strategies and for Reconstructing the Evolution of Hominin Life History

“…This contrasts with folivorous (and provisioned) primates, and helps to explain the fast life histories of mountain gorillas with regard to both dental development and brain growth cessation [12]; for G. beringei food sources are abundant, protein intake is high and competition low. Given the more strongly frugivorous nature of Western lowland gorilla diet [30]–[33] slower maturation rates are therefore expected and, indeed, have been observed [2], [45]–[47]. Although the present study cannot assess the absolute timing of developmental events and, hence, test the “risk aversion hypothesis” [19] directly, the overall habitat structure of the Cameroonian sites makes it parsimonious to infer that the gorillas studied here would follow the general, i.e.…”

“…Behavioural data on West African great apes are rare and insights into gorilla life histories have become available only fairly recently [2], [45]–[47]; information about their skeletal development is extremely limited too [72]. Yet, such information is essential for conservation efforts, for a better understanding of developmental plasticity against ecological conditions [73] and for an appraisal of life history evolution in extinct hominins.…”

“…Resource limitation and mortality are key factors that determine life history strategies in mammals [1], including hominoids [2]. Assessing the relative influence of each of these factors has however been found difficult.…”

“…Available neontological data indicate that juvenile mortality is lower and interbirth intervals are longer in Western lowland gorillas, whilst overall physical maturation proceeds at a much slower pace [2], [46]. Specifically, weaning occurs some 16 months later than in mountain gorillas, such that suckling continues to a median age of 4 ½ years –4 ¾ years [46], [47].…”

“…Specifically, weaning occurs some 16 months later than in mountain gorillas, such that suckling continues to a median age of 4 ½ years –4 ¾ years [46], [47]. The delayed developmental schedule of Western lowland gorillas is therefore more akin to that of chimpanzees [2], [48] than to mountain gorillas [49], [50]. Whether this delay affects all developmental systems equally is not clear however.…”