290 PARTTWO ThePrimates Knott, C.D., and Kahlenberg,S. (2007).In Primatesin Perspective,S. Bearder. C.J.Campbell, A. Fuentes,K.C. MacKinnon and M. Panger,eds. Oxford: Oxford University Press,pp. 290-305. 4*? ad Orangutansin Perspective ForcedCopulations and Female Mating Resistance CherylD, Knott and Sonya M. Kohlenberg INTRODUCTION Though intriguing, this suite of features has proven dif- ficult for researchersto fully understand.The semi-solitary Orangutans (genus Pongo) represent the extreme of many lifestyle of orangutanscombined with their slow life histor- biological para"rneters.Among mammals they have the ies and large ranges means that data accumulate slowly. longest interbirth interval (up to 9 years) and are the largest Also, rapid habitat destruction and political instability in of those that are primarily arboreal. They are the most soli- SoutheastAsia have left only a handful of field sites cur- tary of the diurnal primates and the most sexually dimorphic rently in operation (Fig. 17.1). Despite these difficulties, of the great apes. They range over large areas and do not long-term behavioral studies and recent genetic and hor- have obviously distinct communities. Additionally, adult monal data enable us to begin answering some of the most male orangutanscome in two morphologically distinct types, theoretically interesting questions about this endangered an unusual phenomenonknown as bimaturisnt The smaller great ape. In this chapter, we summarize what is currently of the two male morphs also pursue a mating strategythat is known about the taxonomy and distribution, ecology, social rare among mammals: they obtain a large proportion of organization, reproductive parameters,and conservation of copulations by force. wild oransutans. We also discuss recent advances in our ib:$l{i** :::is:i\ijii*ijlti *u$l€..!*ril:.ri:q :\M rE& {st#tl I i! ' r'eEs' r ra fiffi96|&iGl8 : r: { -*- .%e 't$'n&, tr4 ".f,.i,'":"61"l : !: ,i I'J':::"1;X'1 t *!11-::' ; r' *"-- 1& q, *;** "". ***:.r -r^ fl* , ts, *S;:; Q,*;*trk ':i #*@"*""* *-"1.x, -'* ::.-,--*G" :n '*,* 'qe' Nar sntr* -M il Figl;r* I?.1 Maps of (A) Borneoand (B) Sumatrashowing species and sub-speciesdistinctions, study sites, densities and distributions [modified from Caldecottand Miles (2005)by Kee, L. and Hendrickson,K.l. PIPC02f 11/11/05 17:08 Page 291 Orangutans in Perspective 291 understanding of one distinctive orangutan behavior—forced Taxonomic Status copulations. Formerly, orangutans were classified into two subspecies (Courtenay et al. 1988, Jones 1969). However, orangutan TAXONOMY AND DISTRIBUTION taxonomy has been under recent study and revision, with the majority of molecular and morphological analyses finding Evolutionary History and Past and Present the level of differentiation between Sumatran and Bornean Distribution populations to be equal to or greater than that between the Orangutans evolved in Asia during the Miocene epoch. two species of chimpanzee (Bruce and Ayala 1979, Ferris Sivapithecus, a Miocene ape, was hypothesized to be their et al. 1981, Groves 1986, Janczewski et al. 1990, Ruvolo et al. putative ancestor, based on similarities in the face and palate 1994, Ryder and Chemnick 1993, Uchida 1998, Warren et al. (Pilbeam 1982); but later details of its lower jaw (Ward 1997) 2001, Xu and Arnason 1996, Zhi et al. 1996). Thus, recent and postcrania (Pilbeam et al. 1990) indicate it is instead a taxonomies now elevate the subspecies distinction between sister taxon. The teeth of Lufengpithecus show similarities Sumatran and Bornean orangutans to the species level to those of orangutans (Kelley 2002), but differences in its (Groves 2001), distinguishing them as Pongo pygmaeus in face and periorbital region also exclude it from Pongo Borneo and P. abelii in Sumatra. Warren et al. (2001) esti- ancestry (Chaimanee et al. 2004). Recently, Chaimanee and mate a divergence time of approximately 1.1 million years colleagues (2004) found a new hominoid, Khoratpithecus ago. However, dissenting opinions exist (Muir et al. 1995, piriyai, in Thailand from the early Late Miocene (7–9 million 1998), and Bornean and Sumatran orangutans interbreed in years ago), which shares unique, derived traits with orangutans captivity and produce fertile offspring. Although morphologi- (such as the absence of anterior digastric muscles) and is cal and behavioral differences are emerging between the therefore a likely ancestral candidate. two orangutan species (Delgado and van Schaik 2000), the At the height of their distribution, orangutans ranged level of observed variation does not approach that witnessed throughout the tropical and subtropical regions of eastern within other hominoid genera, such as Pan. and southeastern Asia. Orangutan fossils and subfossils The Bornean species shows further genetic (Warren et al. primarily consist of teeth and jaw fragments found in 2000, 2001; Zhi et al. 1996) and morphological (Groves 1986, China, Thailand, Vietnam, Sumatra, Java, and possibly Groves et al. 1992, Uchida 1998) variation, with most studies Burma and northeastern India (Bacon and Long 2001; Gu pointing to geographically distinct populations, separated et al. 1987; Hooijer 1948, 1960; Kahlke 1972; Pei 1935; in large part by major rivers. Groves (2001) thus separates Schwartz et al. 1994, 1995). These extinct populations the Bornean orangutan into three subspecies: P. pygmaeus had significantly larger teeth than do modern orangutans pygmaeus in Sarawak and northwestern Kalimantan, P. (Bacon and Long 2001, Hooijer 1948, Schwartz et al. 1995). p. wurmbii in southwestern and central Kalimantan, and The first complete fossil orangutan skeleton was recently P. p. morio in Sarawak and east Kalimantan (Fig. 17.1). described (Bacon and Long 2001). The specimen has a Furthermore, analysis of the mitochondrial DNA control re- small body and proportionally longer arms, particularly gion reveals four subpopulations on Borneo that diverged forearms, than legs (Bacon and Long 2001), consistent with 860,000 years ago (Warren et al. 2001). These populations arboreality. correspond to the pygmaeus and wurmbii subspecies, with Orangutans are now restricted to the islands of Borneo the morio subspecies being further subdivided into Sabah and Sumatra. Both ecological and anthropogenic factors and east Kalimantan populations (Warren et al. 2001). seem to be responsible for their range collapse (Delgado and van Schaik 2000). Tropical and subtropical zones shifted Morphology during the Pleistocene (Jablonski 1998, Jablonski et al. 2000), and mean annual temperature rose (Harrison 1999, Often referred to as the “red ape,” orangutans are covered Medway 1977), leading to habitat constriction. Among with thick reddish orange hair. Despite this coloration, other evidence of human influence (Delgado and van Schaik orangutans are often hard to see as they spend over 95% of 2000), orangutan remains found in caves in northern Borneo their time high up in the canopy (Knott 2004). Orangutans show that they were preyed upon by humans (Hooijer 1960, negotiate the canopy through quadrumanual clambering, Medway 1977). grasping supports with both their hands and feet (Knott Orangutans live in true wet rain forests with reported 2004). Morphological adaptations for arboreality include average annual rainfall between 2,000 (Galdikas 1988) and arms, hands, and feet that are longer than those of humans 4,500 (Lawrence and Leighton 1996) mm. The primary and the other great apes (Fleagle 1999) as well as a shallow habitat types they occupy are peat and freshwater swamps hip joint that allows them to hang from any hand–foot and lowland forests. Orangutans have been found living combination because legs can be extended over 90 degrees up to an altitude of 1,200 m; however, their distribution (MacLatchy 1996). declines with increasing elevation (Djojosudharmo and van Orangutans are unusual because males appear to have Schaik 1992). indeterminate growth, meaning that they put on weight PIPC02f 11/11/05 17:08 Page 292 292 PART TWO The Primates (A) (B) Figure 17.2 Photos of (A) flanged and (B) unflanged males from Gunung Palung National Park (photos by Tim Laman). throughout their lives (Leigh and Shea 1995). This growth these males can remain in this stage for over 20 years pattern has been described only for a handful of other mam- (Utami Atmoko and van Hooff 2004) and are fully capable mals and is thought to be associated with intense inter-male of siring offspring (Kingsley 1982, 1988; Utami et al. 2002). competition. Orangutans are also exceptional for having Endocrinological data from captive orangutans show that two morphologically distinct types of adult male (Galdikas the decoupling of fertility and secondary sexual trait devel- 1985a,b; Graham and Nadler 1990; Kingsley 1982, 1988; opment in unflanged males results from gonadotropin and MacKinnon 1979; Maggioncalda et al. 1999, 2000, 2002; testicular steroid levels being sufficient for spermatogenesis Mitani 1985a,b; Schürmann and van Hooff 1986; te Boekhorst but inadequate for triggering secondary sexual maturation et al. 1990). One type is large, weighing over 80 kg in the (Kingsley 1982, Maggioncalda et al. 1999). wild (Markham and Groves 1990), and possesses secondary Wild orangutan females weigh on average 39 kg, which sexual characteristics, including projecting cheek pads or is only 45% of flanged male body size (Markham and Groves “flanges,” a pendulous throat pouch, a coat of long hair, and 1990). This makes orangutans one of the most sexually a musky odor (reviewed