Male orang-utan bimaturism and reproductive success at Camp Leakey in Tanjung Puting National Park, Indonesia

Abstract

Unlike most mammals, male orang-utans exhibit bimaturism, in that mature individuals express one of two distinct morphological forms. Socially subordinate, 'unflanged' males are comparable to females in their size and facial morphology, while socially dominant 'flanged' males exhibit extreme sexual dimorphism and secondary sexual characteristics, primarily in the form of cheek pads ('flanges'). Although male ornaments in other species are often phenotypically plastic, such characteristics in orang-utans are irreversible-and, given that both morphs are sexually mature and can father offspring-their adaptive significance remains unclear. We determined paternity of orang-utans at Camp Leakey in Tanjung Puting National Park, within the home range of one long-term dominant male, Kusasi, before, during and after his period of dominance, in comparison with subordinate male conspecifics. We found that Kusasi fathered substantially more offspring conceived during his dominant period than any other male and that socially subordinate, unflanged males only fathered offspring during periods of rank instability. We conclude that orang-utan male bimaturism is consistent with an evolutionarily stable reproductive strategy and that reproduction within the range of a dominant, flanged male is highly skewed in his favour, while unflanged males may largely wait for reproductive opportunities.

Effective Characterisation of the Complete Orang-Utan Mitochondrial DNA Control Region, in the Face of Persistent Focus in Many Taxa on Shorter Hypervariable Regions

“…Faecal samples were collected from 15 free-ranging Bornean orang-utans in Tanjung Puting National Park, Central Kalimantan, Republic of Indonesia, and genomic DNA extracted, as previously described [51]. Samples were frozen at -20°C for up to five years prior to DNA extraction.…”

A comparison of paternity data and relative testes size as measures of level of sperm competition in theHominoidea

“… References: A, “Extra‐Pair Paternity Confirmed in Wild White‐Handed Gibbons,” by Barelli et al, , American Journal of Primatology, 75, p. 1185; B, “Wild Gibbons' Parentage Tested by Non‐Invasive DNA Sampling and PCR‐Amplified Polymorphic Microsatellites,” by Oka and Takenaka, , Primates, 42, p. 67; C, “Extrapair Paternity in Golden‐Cheeked Gibbons ( Nomascus gabriellae ) in the Secondary Lowland Forest of Cat Tien National Park, Vietnam,” by Kenyon et al, , Folia Primatologica, 82, p. 154; D, “Male Bimaturism and Reproductive Success in Sumatran Orang‐Utans,” by Utami et al, , Behavioral Ecology, 13, p. 643; E, “Male Orang‐Utan Bimaturism and Reproductive Success at Camp Leakey in Tanjung Puting National Park, Indonesia,” by Banes et al, , Behavioral Ecology and Sociobiology, 69, p. 1785; F, “Mountain Gorilla Tug‐of‐War: Silverbacks Have Limited Control Over Reproduction in Multimale Groups,” by Bradley et al, , Proceedings of the National Academy of Sciences at the United States of America, 102, p. 9418; G, “Male Rank, Not Paternity, Predicts Male–Immature Relationships in Mountain Gorillas, Gorilla beringei beringei ,” by Rosenbaum et al, , Animal Behaviour, 104, p. 13; H, “Dispersed Male Networks in Western Gorillas,” by Bradley et al, , Current Biology, 14, p. 510, I, “Male Genetic Structure and Paternity in Western Lowland Gorillas ( Gorilla gorilla gorilla ),” by Inoue et al, , American Journal of Physical Anthropology, 151, p. 583; J, “Intracommunity Relationships, Dispersal Pattern and Paternity Success in a Wild Living Community of Bonobos ( Pan paniscus ) Determined from DNA Analysis of Faecal Samples,” by Gerloff et al, , Proceedings of the Royal Society of London. Series B, Biological Sciences, 266, p. 1189; K, “The Chimpanzees of the Tai Forest,” by Boesch and Boesch‐Achermann, , Oxford University Press, London, England; L, “Male Competition and Paternity in Wild Chimpanzees of the Taï Forest,” by Boesch et al, , American Journal of Physical Anthropology, 130, p. 103; M, “Male Dominance Rank and Reproductive Success in Chimpanzees, Pan troglodytes schweinfurthii ,” by Wroblewski et al, , Animal Behaviour, 77, p. 873; N, “Paternity Discrimination and Inter‐Group Relationships of Chimpanzees at Bossou,” by Sugiyama et al, , Primates, 34, p. 545; O, compiled from “How Well Does Paternity Confidence Match Actual Paternity?…”

“…Unflanged males are in a state of delayed maturation. However, both male morphs are fertile, sexually active, and sire offspring (Banes, Galdikas, & Vigilant, ; Goossens et al, ; Kingsley, ; Maggioncalda, ; Utami et al, ). They do, however, pursue different sexual strategies.…”

“…Paternity data are available (Table ) for both species: P. abelii (Utami et al, ; see also the same data in Utami Atmoko et al, ); and P. pygmaeus (Banes et al, ). For P. abelii , the paternity data are presented in two different ways: (a) with an observed consort (flanged or unflanged) to the female as the Designated Male; and (b) with the female's local, flanged, dominant, and territorially resident male as the Designated Male.…”

“…One concern expressed by the authors of the different studies was that a proportion of the orangutans involved in each study had either been released into the wild or were the descendants of such rehabilitated individuals (Banes et al, ; Utami Atmoko et al, ). Another concern was that the dominant male which was the main focus of the study by Banes et al () received veterinary assistance for the last few years of his waning dominance. Finally, a concern was expressed that dominant males appear relatively uninterested in nulliparous females who therefore consort more with subordinate males, particularly unflanged (Utami Atmoko et al, ).…”