Potamochoerus Gray, 1854

Leslie, David M., Jr & Huffman Abstract, Brent A., 2015, Potamochoerus porcus (Artiodactyla: Suidae), Mammalian Species 47 (919), pp. 15-31 : 15-24

Potamochoerus Gray, 1854

Sus Linnaeus, 1758:49 . Part ( Sus porcus Linnaeus, 1758 ).

Sus: F. Cuvier, 1822:447 . Part ( Sus larvatus F. Cuvier, 1822 ).

Sus: Desmoulins, 1831:139 , plate CXLVI, figure 2. Part ( Sus koïropotamus Desmoulins, 1831 ).

Koiropotamus Gray, 1843:xxvii. Nomen nudum.

Choiropotamus Gray, 1843:185 . Nomen oblitum, vide Grubb (2004, 2005); preoccupied by Chaeropotamus G. Cuvier, 1821 (Helohyidea) , vide Kretzoi and Kretzoi (2000).

Potamochoerus Gray, 1854:130 . Type species Choiropotamus pictus Gray, 1852 (= Sus porcus Linneaus, 1758 ), by original designation; nomen protectum of Choiropotamus Gray, 1843 .

Nyctochoerus Heuglin, 1863:7 . Type species Nyctochoerus hassama Heuglin, 1863 (= Sus larvatus F. Cuvier, 1822 ), by original designation.

Koiropotamus: Dietrich, 1937:97, footnote 1. Not Potamochoerus Gray, 1854 ; based on a Pleistocene fossil from Oldoway, Africa, considered to be Mesochoerus Shaw and Cooke, 1941 by Harris and White (1979).

Potamochoerus: Leakey, 1942:183 , plate 61. Not Potamochoerus Gray, 1854 ; based on a Pleistocene fossil from Oldoway, Africa, considered to be Mesochoerus Shaw and Cooke, 1941 by Harris and White (1979).

Potamochoerus: Leakey, 1967:32 , plate 28. Not Potamochoerus Gray, 1854 ; based on a Pleistocene fossil from Oldoway, Africa, considered to be Mesochoerus Shaw and Cooke, 1941 by Harris and White (1979).

Potamochaerus Breuer, Barrell Mavinga, and Breuer-Ndoundou Hockemba, 2009:551. Incorrect subsequent spelling of Potamochoerus Gray, 1854 .

CONTEXT AND CONTENT. Order Artiodactyla , suborder Suina , family Suidae , subfamily Suinae . Potamochoerus was generally considered to be monotypic until the early 1990s, but now 2 species are recognized ( P. larvatus [bushpig] and P. porcus — Grubb 1993b, 2005; Groves and Grubb 2011; Meijaard et al. 2011).

Potamochoerus porcus ( Linnaeus, 1758) Red River Hog

[ Sus ] Porcus Linnaeus, 1758:50 . Type locality “Habitat in Africa;” restricted to “West Africa … based on animals exported to Brazil ( Simoons 1953)” by Grubb (2005:639).

Sus Guineensis Pallas, 1766:18 . Type locality “Africae.”

Sus penicillatus Schinz, 1848:12 , table 10. Type locality “ Habitat in Africa occidentali.”

Choiropotamus pictus Gray, 1852:280 . Type locality “ Camaroon River, West Africa. ”

Potamochoerus penicillatus: Gray, 1854:129 , plate xxxiv. Name combination.

Potamochoerus albifrons Du Chaillu, 1860:301 . Type localities “between Cape Lopez [ Gabon] and Cape St. Catherine, and on the head waters of the Fernand-Vaz River,” western Equatorial Africa .

Potamochoerus porcus: Gray, 1868:36 . First use of current name combination.

S [us]. [choeropotamus] porcus: de Poncins, 1899:523 . Name combination.

Potamochoerus porcus pictus: Lönnberg, 1910:7 . Name combination.

Potamochoerus porcus ubangensis Lönnberg, 1910:10 . Type locality “ Ubangui , Northern Congo.”

Potamochoerus porcus albifrons: Lönnberg, 1910:11 . Name combination.

P [otamochoerus]. p [orcus]. congicus Lönnberg, 1910:14. Type locality “ Lower Congo.”

Potamochoerus porcus albinuchalis Lönnberg, 1919:245 . Type locality “district of Lake Leopold II [= Lake Mai-Ndombe],” western Democratic Republic of the Congo.

Potamochoerus porcus mawambicus Lorenz-Liburnau, 1923:92 . Type locality “Mawambi,” Haut-Zaire , Democratic Republic of the Congo, Africa.

Choiropotamus porcus: Rosevear, 1939:104 . Name combination.

Ch [oiropotamus]. porcus pictus: Rosevear, 1939:105 . Name combination.

CONTEXT AND CONTENT. Context as for genus. No subspecies of Potamochoerus porcus ( Fig. 1 ) are currently recognized ( Grubb 1993b, 2005; Groves and Grubb 2011; Meijaard

et al. 2011), although various geographical subspecies have been named in the past. An east–west cline in body size was noted by Vercammen et al. (1993) between eastern Democratic Republic of the Congo (larger) and Cameroon (smaller), but Grubb (1993b) did not find sufficient morphometric differences throughout the distribution of P. porcus to recognize any subspecies.

NOMENCLATURAL NOTES. Taxonomic distinction between Potamochoerus porcus and P. larvatus has been mixed, particularly prior to the early 1990s. Lönnberg (1910) recognized 5 species of Potamochoerus : porcus , choeropotamus, larvatus , hassama , and intermedius (an intermediate form between his western porcus -group and his eastern choeropotamus -group). de Beaux (1924) reconsidered Lönnberg’s (1910) classification and reduced Potamochoerus to the 3 species porcus , intermedius, and larvatus and designated choeropotamus and hassama as subspecies of larvatus . Schouteden (1945) recognized 2 species: porcus with 3 subspecies ( porcus , albifrons , and ubangensis) and larvatus with 3 subspecies ( larvatus , congicus, and johnstoni). Similarly, Mohr (1960) used 2 species, but they were porcus and choeropotamus. In keeping with Haltenorth (1963), Ansell (1971) recognized only a single species, porcus , under which he placed 13 subspecies (including larvatus ), but he noted that some of these subspecies were based on limited material. The common treatment from the 1970s to the early 1990s was to recognize 1 species ( porcus ) with 2 subspecies: the nominate form and larvatus (e.g., Kingdon 1979; Estes 1991). Grubb (2005) designated no subspecies of P. porcus but listed 6 subspecies of P. larvatus : edwardsi, hassama , koiropotamus , larvatus , nyasae, and somaliensis. Currently, P. porcus is considered monotypic, and the number of subspecies of P. larvatus is in dispute: hassama , larvatus , and somaliensis according to Groves and Grubb (2011) and hassama , koiropotamus , and somaliensis according to Meijaard et al. (2011), who omitted larvatus because of its contentious 1st description from Madagascar (F. Cuvier 1822) and the likelihood that it was introduced there.

Because of the wide variety of historical taxonomic approaches, care was given in this synthesis to assess the locations where studies were conducted relative to distributional information of the 2 currently recognized species of Potamochoerus ( Fig. 1 ; Grubb 1993a, 1993b, 2005; Groves and Grubb 2011; Meijaard et al. 2011). Nevertheless, P. porcus and P. larvatus no doubt share many morphological, ecological, and behavioral characteristics, so some information for P. larvatus , likely similar for P. porcus , has been included here.

The generic name Potamochoerus is from the Greek words “potamos” meaning river and “khoiros” meaning pig; the specific epithet porcus is the Latin word meaning pig. “River pig” aptly describes habitat preferences of P. porcus . Similarly, the common name, “red river hog,” refers to its reddish coat color and distribution near water (i.e., “red riverhog”— Lydekker 1915) and is not related to a formal name of a river. Depending on the language and country, P. porcus is called mboye (Kiliangulu) and opegu (Madi— Kingdon 1979); n’gouyi, n’gouloubou, n’goua, n’gu, and n’gouyo (Central African dialects—Malbrant and Maclatchy 1949); pamé (Babinga—Malbrant and Maclatchy 1949); potamochère or potamochère roux (French) and porc à pinceau (French, referring to the tufted ears— Dosimont 2004); Pinselschwein or Pinselohrschwein (German, “tufted pig” or “tufted-ear pig”); and, historically, tufted pig and painted pig in English. Images of P. porcus have been featured on several postage stamps, including in Côte d’Ivoire, Liberia, Republic of Burundi, and the former Spanish colony of Rio Muni, now Equatorial Guinea ( Gewalt 1988; Braasch and Meijaard 2014).

DIAGNOSIS

Potamochoerus porcus is 1 of 8 wild suids in Africa ( Grubb 1993b). Externally, P. porcus can be easily distinguished from all other African swine by its rufous-to-russet coat and thin white dorsal crest ( Gray 1854:plate XXXIV; Fig. 2 ); black forehead with contrasting white “spectacles;” and leaf-shaped, elongated ears that end in long tufts of hair ( Gray 1868; Happold 1987; Grubb 1993b; Vercammen et al. 1993; Kingdon 1997). The Eurasian wild pig ( Sus scrofa algira ) in North Africa is easily distinguished due to its allopatric distribution, occurring in extreme coastal montane areas of northwestern Africa (Cuzin and Randi 2013); it has “black [pelage] with yellowish or reddish tips, dark brown underwool, and not much of a mane” ( Meijaard et al. 2011:289). Among the other 6 Afrotropical suids (occurring south and east of the Sahara proper), most have sparse grayish or blackish pelage, including the 3 newly elevated species of forest hogs ( Hylochoerus meinertzhageni , H. rimator , and H. ivoriensis —Groves and Grubb 2011, who did not provide common names), common warthog ( Phacochoerus africanus ), and desert warthog ( Phacochoerus aethiopicus ). Coloration of the congeneric Potamochoerus larvatus is extremely variable, ranging from “blond, pale red, or russet up to a dark brown or near-black shade” ( Meijaard et al. 2011:279).

Pelage of P. larvatus is much shaggier than that of P. porcus , particularly along the dorsum where it forms a distinctive wide mane ( Grubb 1993b). P. porcus can be further distinguished from P. larvatus by the presence of “masked” facial markings (dark forehead and white lines around the eyes), although the unmasked head of P. larvatus usually contrasts in color with the body ( Grubb 1993b). Tones and patterns of P. larvatus tend to be most similar to P. porcus in areas of near-sympatry, which has been suggested to indicate some degree of hybridization ( Lönnberg 1910; Kingdon 1979; Ghiglieri et al. 1982). Nevertheless, Grubb (1993b:68) noted that introgression between P. porcus and P. larvatus had never been adequately documented and that besides a similarity in overall coloration, so-called intermediate animals had “no special resemblances to P. porcus ...in face pattern, type of pelage or ear shape.”

GENERAL CHARACTERS

Potamochoerus porcus is the smallest of the Afrotropical suids (head–body length, 100–145 cm; tail length, 30–45 cm; shoulder height, 55–80 cm; mass, 45–115 kg — Meijaard et al. 2011). It is most comparable to P. larvatus : 100–150 cm; 30–40 cm; 55–88 cm; 50–115 kg — Meijaard et al. 2011) and the Eurasian wild pig in northwestern Africa ( Grubb 1993b). P. porcus is least comparable to forest hogs (130–210 cm; 25–45 cm; 75–110 cm; 140–275 kg for males and 100–200 kg for females) and common warthog (125–150 cm for males and 105–140 cm for females; 35–50 cm; 55–85 cm; 60–150 kg for males and 50–75 kg for females— Meijaard et al. 2011).

Males of P. porcus tend to be heavier than females, although sexual size dimorphism is poorly resolved in other external measurements (Malbrant and Maclatchy 1949). Few primary-source body measurements are available; data from 8 males and 11 females from Kango, Gabon, indicate a head–body length of 94.0–117.0cm (mean: 110.3 cm for males and 107.0 cm for females); shoulder height, 52.5–67.0 cm (mean: 61.0cm for males and 56.7cm for females); and tail length, 39.5–46.5cm (mean: 43.9cm for males and 41.8 cm for females—Malbrant and Maclatchy 1949). Wholebody weights from this data set were restricted to 2 females (54 and 55 kg) and 4 males (52–80 kg; mean = 67 kg). Overall form of the body of P. porcus is thickset and rounded, and legs are rather short ( Happold 1987). Radiographs of the forelimb of P. porcus were used to illustrate the unguligrade design (“hoof walking”) typical of all hoofed ungulates, whereby weight-bearing occurs on the 3rd and 4th toes with the loss of the 1st metacarpal (Gough- Palmer et al. 2008:figure 6) .

Adult coloration is always bright orange or reddish-brown—a key distinguishing feature of P. porcus ( Johnston 1906; Lydekker 1915). The entire body is covered by short, dense pelage such that (in contrast to other Afrotropical suid genera) no bare skin is visible ( Johnston 1906; Lydekker 1915); additional long bristles are scattered along the lower flanks (Malbrant and Maclatchy 1949; Happold 1987). A thin dorsal crest of long white hairs extends from nape of neck to partway down tail ( Lydekker 1915; Malbrant and Maclatchy 1949). The tail itself is long, tapered, and very slender, colored predominantly like the body but with a black terminal tuft (Malbrant and Maclatchy 1949; Happold 1987). P. porcus has an elongated head and flattened rostral disc ( Happold 1987). In immature individuals, the head is the same rufous color as the body ( Lydekker 1915), but adults develop a striking facial mask: a black wedge on the forehead extending from the ears downward between the eyes ( Fig. 1 ), and bright white markings encircling the eyes, often interrupted in the temporal region (Malbrant and Maclatchy 1949).

Adult males of P. porcus are readily distinguished from females by the presence of prominent cone-shaped protuberances on either side of the muzzle (Malbrant and Maclatchy 1949; Fig. 3 ). Males also develop inflated mandibular and suborbital ridges that are emphasized by the presence of long white whiskers and a dark blackish-red band situated between them (Malbrant and Maclatchy 1949; Vercammen et al. 1993). Similar white whiskers may be present in females, but they are always in reduced form (Malbrant and Maclatchy 1949).

The distinctive ears of P. porcus are leaf-shaped with very extended termini. The external surfaces are black, and the upper margins white ( Lydekker 1915; Malbrant and Maclatchy 1949). Long tufts or “pencils” ( Du Chaillu 1860:302) of hair at the ends of the pointed ears can grow to 12.7 cm in length or longer. Depending on the locale, these tufts may be black (prevalent in eastern populations, e.g., Democratic Republic of Congo —Malbrant and Maclatchy 1949), white (West Africa, e.g., Liberia — Johnston 1906), or mixed (e.g., in Gabon; Fig. 1 ).

Canine teeth develop into sharp tusks in males; the upper canines flare upward but rub against the corresponding lower tusks and both thereby remain relatively short (upper canines 20 mm and lower canines 47 mm — Dosimont 2004; rarely to 120 mm — Malbrant and Maclatchy 1949). Typically, tusks of P. porcus are not especially visible outside of the mouth, as they are in warthogs ( Happold 1987). When a lower canine is absent, the corresponding upper canine grows in an upward curve; Malbrant and Maclatchy (1949) reported one such specimen with a tusk of 298 mm. Canines of female P. porcus are reduced in length ( Groves 1981).

DISTRIBUTION

Potamochoerus porcus is widespread in the rainforest belt of western and central Africa, including Benin, Cameroon, Central African Republic, Côte d’Ivoire, Democratic Republic of the Congo, Equatorial Guinea, Gabon, Ghana, Guinea, Guinea Bissau, Liberia, Nigeria, Republic of Burundi, Republic of Rwanda, Senegal, Sierra Leon, and Togo, with no reliable records from or uncertain presence in Gambia, Chad, South Sudan, and southwestern Ethiopia ( Grubb 1993a, 1993b, 2005; Grubb et al. 1998; Wild Pig Specialist Group 2013; Fig. 4 ). The eastern distribution of P. porcus abuts that of P. larvatus ( Vercammen et al. 1993:figure 9), and early reports suggested that the 2 species hybridized (e.g., Lönnberg 1910; Kingdon 1979), for example, in the Kibale Forest, Uganda ( Ghiglieri et al. 1982). Grubb (1993b) considered such claims to be erroneous and concluded that no cases of interbreeding had been adequately documented. He further noted that sympatry between the 2 species is possible (but yet to be confirmed) in the Rift Highlands of the Democratic Republic of the Congo, Republic of Burundi, and Republic of Rwanda but that P. porcus and P. larvatus are separated by elevation, with P. larvatus only occurring on mountain slopes and P. porcus only occurring in lowland forests.

FOSSIL RECORD

The earliest fossils from the families Suidae ( Siamochoerus banmarkensis — Ducrocq et al. 1998) and Tayassuidae ( Egatochoerus jaegeri — Ducrocq 1994) have been found in Thailand in southeastern Asia and date to the late Eocene about 38 million years ago. Prior to these discoveries, the earliest fossil suid was thought to be Palaeochoerus , derived from Propalaeochoerus , from the Oligocene, 23–34 million years ago ( Pilgrim 1940; Thenius 1970; Cooke and Wilkinson 1978; Groves 1981; Carroll 1988). Early forms of Tayassuidae eventually moved northeasterly into North America and subsequently into South America, giving rise to extant peccaries (e.g., Mayer and Wetzel 1986, 1987), and early forms of Suidae moved into western Asia, Europe, and Africa, with somewhat uncertain centers of diversification and radiation (e.g., Pilgrim 1926, 1940; Cooke and Wilkinson 1978). Fossil species of Suidae from throughout the Miocene (about 5–23 million years ago) are well represented on the Indian subcontinent, Europe, and Africa ( Pilgrim 1926, 1940; Leakey 1942, 1967; Maglio 1978; Harris and White 1979). Nevertheless, the sequence of continental immigrations and emigrations in the early evolution of suids is less clear than in peccaries; Cooke and Wilkinson (1978:452) suggested that at least 3 major “burst[s] of adaptive radiation” occurred from the early Miocene through the Plio-Pleistocene, but they concluded that “it [was] impossible to state unequivocally which continent witnessed the emergence of the true suids.”

Maglio (1978) summarized the fossil record of suid genera in Africa throughout the Cenozoic, beginning in the early Miocene with the appearance of Hyotherium , Kubanochoerus , Lopholistriodon , Xenochoerus , Sanitherium , and Nyanzachoerus and possibly Propalaeochoerus and Listridon. All of those genera, except Nyanzachoerus , were absent from the fossil record by the mid-Miocene about 14 million years ago. Six suid genera made their appearance in the African Pliocene, 2.6–5.0 million years ago, including the species-rich and wide-ranging extinct genus Kolpochoerus (e.g., Cooke and Wilkinson 1978; Harris and White 1979; Haile-Selassie and Simpson 2013) and Phacochoerus , represented today by the common warthog and desert warthog. An additional 4 genera appeared in the early and Middle Pleistocene, including Potamochoerus (represented today by P. porcus and P. larvatus ) and Hylochoerus (3 modern species of forest hogs: Hylochoerus meinertzhageni , H. rimator , and H. ivoriensis ). Maglio’s (1978) record reflects when a particular genus appeared in the African fossil record, not the point when a particular form came to be. Nevertheless, it is clear that rapid diversification of sub-Saharan suid species occurred during the Plio-Pleistocene, with 7–9 fossil and extant genera and 16–21 species (White and Harris 1977; Cooke 1978; Harris and White 1979). Bishop (1994:i) found that “maximum species diversity of the Hominidae and the Suidae [in Africa] is roughly synchronous, occurring between 2.0 and 1.7 million years ago.”

Morphological similarities suggest that Potamochoerus evolved from a Sus -like ancestor (Cooke 1978; Kingdon 1979; Groves 1981), likely in the mid-Miocene in Asia, with Potamochoerus forms first appearing in Europe in the mid- Pliocene ( Pilgrim 1940) and in Africa in the Middle Pleistocene ( Maglio 1978), perhaps earlier (Harris and White 1979). The appearance and disappearance of Potamochoerus in the African fossil record are very punctuated, suggesting a rather sudden immigration from elsewhere and/or relegation to habitats with limited fossilization, perhaps because of competition with newly arrived forms of Mesochoerus and Metridiochoerus , now extinct (Harris and White 1979; White et al. 2006).

Assessments of mitochondrial and nuclear DNA of extant Suinae from Eurasia and Africa provide the most contemporary theory on the evolution of sub-Saharan suids, including the origins of P. porcus ( Gongora et al. 2011) . Unlike earlier morphological assessments (e.g., Thenius 1970; Groves 1981), Gongora et al. (2011:332) found that all extant Afrotropical suids “are phylogenetically distinct from Eurasian Sus and Porcula [pygmy hog] and that Hylochoerus – Phacochoerus form a [monophyletic] sister clade to Potamochoerus .” Divergence times suggest that Sus and what are now the 3 sub-Saharan genera diverged 7.2–14.5 million years ago; Potamochoerus diverged from Hylochoerus – Phacochoerus forms 5.6–11.9 million years ago; and P. porcus and P. larvatus diverged 0.2–4.8 million years ago ( Gongora et al. 2011). Some of these divergence estimates predate the occurrence of suid fossils in Africa, tentatively suggesting that all extant sub-Saharan suids “diverged from their common ancestors outside Africa” ( Gongora et al. 2011:333). Additional fossil material and genetic analyses will no doubt refine these scenarios.

FORM AND FUNCTION

Skull measurements among the Afrotropical suids are somewhat more disparate than body mass, particularly among some of the subspecies. Greatest length of skull from occipital crest to tip of premaxillae (mm) is: Potamochoerus porcus , 327–405 for males and 269–378 for females; P. larvatus hassama , 341–377 for males and 327–353 for females; P. l. koiropotamus , 367– 415 for males and 345–395 for females; and the 3 giant forest hogs, Hylochoerus ivoriensis , 355–397 for males and 333–372 for females; H. rimator , 341–404 for males and 330–391 for females (specimens from Cameroon, Congo, and Zaire); and H. meinertzhageni , 410–461 for males and 381–427 for females ( Grubb 1993b; Groves and Grubb 2011).

Groves (1981) noted that the skull of P. porcus has a very elongated facial profile; deep preorbital fossa; well-developed temporal ridges; open-rooted canines that flare upward and laterally (most notable in males); and bony protuberances in males that grow upward from near the upper canine sheaths— absent in all other living suid genera ( Fig. 5 ). These protuberances are “hypertrophied apophyses” and end with a terminal cutaneous wart; they likely evolved to protect tendons running to the musculature of the snout during head-to-head combat of males involving their upper canines ( Ewer 1956, 1958; Groves 1981; Grubb 1993b:66). Potamochoerus lacks “infraorbital warts or swellings, as in other Afrotropical genera” of suids ( Grubb 1993b:66). Three specialized muscles, which occur in all suids but are particularly developed in P. porcus , give the snout great mobility: the levator rostri that pulls the snout up and back, dilator naris lateralis that pulls the snout disk backward, and depressor rostri that pulls the snout down ( Ewer 1958; Groves 1981).

Potamochoerus porcus (along with P. larvatus ) retains ancestral dentition (i 3/3, c 1/1, p 3–4/3–4, m 3/3, total 40–44— Sowls and Phelps 1968; Meijaard et al. 2011; Groves 2013), comparable to the Eurasian wild boar (i 3/3, c 1/1, p 4/4, m 3/3, total 44—Cuzin and Randi 2013). Canines (tusks) of male P. porcus are more developed than in females; the upper canines flare outward but are worn down by the lower canines—the latter are thereby sharped into effective weapons ( Groves 1981). Premolars are enlarged and molariform ( Groves 1981); molars themselves are brachydont and covered with thick enamel ( Grubb 1993b). Chewing is performed with a simple chopping action ( Groves 1981). Dentition of P. porcus is consistent with a frugivorous diet, in contrast to the hypsodont molars of grazing warthogs ( Clauss et al. 2008).

Glands of P. porcus are likely similar to those of the congeneric P. larvatus : both sexes have Harderian glands (found in the eye sockets) and digital glands; maxillary tusk glands and preputial glands are restricted to males (Leus and Vercammen 2013). A chin gland or “mental-organ,” about 20 mm in diameter and raised 2–5 mm in adults with 8–11 sinus hairs, probably has a tactile function; it is already noticeable in a 20-mm embryo ( Mohr 1960:13; De Boer 1980 [not seen, cited in Leus and Vercammen 2013:37]). Although not specifically confirmed in the literature on P. porcus , males of P. larvatus have a swollen pouch (57 mm by 87 mm in size) behind each upper canine; maxillary tusk glands therein secrete copious amounts of a white, oily substance probably used for scent marking ( Jones 1978; Kingdon 1979). The pouches are often full of woody debris, collected as the canines are scraped on vegetation ( Jones 1978), and house a commensal nematode ( Rhabditis — Marlow 1955).

Females have 6 mammae ( Macdonald 2000). Males have very large, paired Cowper’s glands (= bulbourethral glands— Walker 1922a, 1922b), located near the urethra at the base of the penis and associated with pre-ejaculatory secretions that flush the urethra before ejaculation; these glands are about 17–18 cm long and 5 cm in diameter in domestic pigs ( McEntee 1990). Mass of the testes fluctuates seasonally (65–113 g — Meijaard et al. 2011). The suid penis is “long, sigmoidally curved … [ending] in a corkscrew shape and lacks a glans” ( Meijaard et al. 2011:262).

ONTOGENY AND REPRODUCTION

Ontogeny. —Neonates of Potamochoerus porcus weigh 650–900 g at birth ( Benirschke 2002) and are dark brown in color with a distinctive pattern of yellowish longitudinal stripes and spots ( Johnston 1906; Kingdon 1979; Grubb et al. 1998; Leus and Vercammen 2013; Fig. 6 ). Body temperature of neonates is high (typically 38°C measured rectally), and they have poor thermoregulatory abilities and are sensitive to cold ( Dosimont 2004). Neonatal suids use shivering to produce heat; they apparently lack brown adipose tissue and thus cannot produce heat by nonshivering thermogenesis (Herpin and Le Dividich 1995). Female P. porcus builds birthing nests (Abernethy and White 1999), which may mitigate the need for such thermoregulation ( Curtis 1995; Herpin and Le Dividich 1995). Berg et al. (2006) demonstrated that mitochondrial uncoupling protein 1, which is involved with dissipation of heat during fat metabolism, was inactivated in the suid lineage about 20 million years ago.

Milk composition of the congeneric P. larvatus is 24.2% total solids, 10.4% total fat, 9.4% protein, and 3.0% sugar ( Seydack 1990 [not seen, cited in Macdonald 2000:222]).Young are weaned in about 120 days ( Macdonald 2000). The neonatal pattern of pale stripes is replaced by overall reddish pelage at about 6 months of age ( Kingdon 1979; Grubb et al. 1998; Leus and Vercammen 2013). Male and female P. porcus are fully grown at 2 years of age ( Kingdon 1997), and sexual maturity seems to be reached by both sexes at 3 years ( Hayssen et al. 1993; Benirschke 2002). Under captive conditions, individuals may mature earlier: females have given birth as young as 22 months of age (i.e., conceived at 18 months), and males may be reproductively active as young as 19 months ( Holland 2013). Reproductive senescence has been poorly studied, but males as old as 17 and females up to 13 years of age have produced offspring in captivity ( Holland 2013).

Reproduction. — Potamochoerus porcus is a seasonal breeder across its distribution, with births typically occurring from the latest part of the dry season in February through the 1st one-half of the rainy season in July ( Bates 1905; Verheyen 1985; Hayssen et al. 1993; Kingdon 1997). In Gabon, Malbrant and Maclatchy (1949) recorded pregnant females in mid- December and early March, and in western Nigeria, neonates have been recorded in February–March ( Happold 1987). Under captive conditions in Gabon, 2 distinct birthing periods were observed: June–July and November–January ( Dosimont 2004).

Reproduction ex situ follows a similar trend to the wild. In North American zoos, 88% of births have occurred between March and August ( Holland 2013); in the United Kingdom, the initial breeding successes in the mid-1800s occurred between June and October ( Zuckerman 1952). Nevertheless, breeding in captivity occurs year-round, and births in North American zoos have been recorded in every month except February ( Holland 2013). Interbirth interval is typically given as 1 year ( Verheyen 1985), but a pair of P. porcus in the Duisburg Zoo, Germany, produced 3 consecutive litters at 8-month intervals ( Gewalt 1988).

The estrous cycle of P. porcus has been reported to be about 30 days ( Macdonald 2000), with recent assessment of fecal steroids suggesting a more precise estimate of 34–37 days ( Berger et al. 2006). Gestation is about 120 days ( Vercammen et al. 1993; Kingdon 1997; Leus and MacDonald 1997; Macdonald 2000), after which a litter of 1–6 (typically 3–4) piglets is born ( Bates 1905; Zuckerman 1952; Verheyen 1985; Hayssen et al. 1993; Vercammen et al. 1993). Aspects of the placental anatomy of P. porcus have been described from captive individuals at the San Diego Zoo, California ( Benirschke 2002). The villous placenta is of uniform thickness—a maximum of 2 mm —with folds of the chorionic trophoblastic surface and no invasion of the uterus; full-term, twin placentae from surviving neonates weighed 275 and 300 g and were 83 and 85 cm in length and 5 and 13 cm in width, with umbilical cords inserted midlaterally and large allantoic sacs; and ends of placenta showed degenerative change at full term ( Benirschke 2002). The fetal–placental surface had a “slimy, glassy, edematous appearance,” typical of suids ( Benirschke 2002:webpage 4).

ECOLOGY

Population characteristics. —Information on population characteristics of wild Potamochoerus porcus is limited. In Nigeria, a 2:1 ratio of immature individuals to adults was reported by Oduro (1989 [not seen, cited in Leus and Vercammen 2013:39]). A wild-born female in the Frankfurt Zoo, Germany, lived at least 21 years and 7 months ( Weigl 2005). Maximum life span of P. porcus in the wild is unknown but probably considerably less than in captivity; Leus and Vercammen (2013) suggest an average maximum life span of 15 years. Leus and Vercammen (2013:38) recently summarized some studies of density (individuals/km 2) of P. porcus , noting considerable variation among locations and habitat types: 1.3–5.6 (0.04–0.17 groups/km 2) in the forested areas of Lopé National Park, Gabon ( White 1994); 18.4 in galleries and bosquets of the savanna ecotone in Lopé National Park ( Tutin et al. 1997); 3.1 in Equatorial Guinea ( Fa et al. 1995); and 2.0 in Réserve de Faune à Okapis, Ituri Forest, Democratic Republic of the Congo ( Hart et al. 1996). Other studies have shown densities of 7.31 individuals/km 2 and 0.26 groups/km 2 in coastal forests of Réserve de Faune du Petit Loango, Gabon (now Parc National de Loango— Morgan 2007); 4.74 (95% CI 3.22–6.55) near Campo-Ma’an, Cameroon, based on “pooling local expert opinions” ( van der Hoeven et al. 2004:193); and 1.52 in Taï National Park, Côte d’Ivoire ( Hoppe-Dominik et al. 2011).

Potamochoerus porcus can be a substantial part of the mammalian biomass in Central African rainforests. In Lopé Reserve (now Lopé National Park), P. porcus ranked 3rd (1,136 kg / km 2) behind the African forest elephant ( Loxodonta cyclotis ; 2,125.2 kg /km 2) and the forest buffalo ( Syncerus nanus ; 1,752.8 kg /km 2 — Tutin et al. 1997). In Parc National de Loango, based on observational censuses, biomass of P. porcus ranked 2nd (452.5 kg /km 2) but was considerably below that of the African forest elephant (4,476.2 kg /km 2 — Morgan 2007). Estimates of abundance of rainforest ungulates, such as P. porcus or duikers ( Philantomba and Cephalophus ), are difficult to make based on counts of fecal droppings alone because feces can decay within a few hours and disappear within minutes due to dung beetle (subfamily Scarabaeinae ) activity, so a combination of census methods, including direct observation or mark-recapture approaches, are recommended but not always achieved ( Breuer et al. 2009; Van Vliet et al. 2009). For these reasons, some earlier estimates of the biomass of P. porcus (e.g., 51 kg /km 2 in Ogooué-Maritime Province, southwestern Gabon, where Parc National de Loango is located—Prins and Reitsma 1989) might be low.

Space use. — Potamochoerus porcus generally prefers damp forests ( Fig. 7 ). It can be found in a variety of habitats throughout its distribution, but never far from thick vegetative cover, soft soils (for rooting), and water ( Kingdon 1979, 1997; Grubb et al. 1998; Leus and Vercammen 2013). In Ghana, P. porcus was captured in savanna, semi-deciduous forest, and coastal habitats ( Ntiamoa-Baidu et al. 2005). In Dzanga-Ndoki National Park, southwestern Central African Republic, P. porcus most often used mixed forest (with a wide range of understory density) but was seen in 5 vegetative types including open grassy clearings ( Melletti et al. 2009; Fig. 7 ). Abundance of P. porcus was positively associated with presence of major roads and high traffic in coastal Gabon, suggesting that improved foraging from regrowth of vegetation along roads may outweigh the risks of human disturbance ( Vanthomme et al. 2013).

There is no specific information on movements and home range of P. porcus , but home ranges of related P. larvatus in dry forests of South Africa were 3.8–10.1 km 2, and individuals moved 0.48–5.84 km /day, covering all of their home ranges every 1–4 days ( Seydack 2013). Great variations in densities and large aggregations have suggested to some observers that P. porcus “migrates,” perhaps moving long distances to take advantage of patchy fruit production (Malbrant and Maclatchy 1949; Abernethy and White 1999; Leus and Vercammen 2013:38).

Diet. — Potamochoerus porcus is omnivorous, preferring roots and tubers and seasonally eating a wide variety of fruits and seeds; insects, eggs, and small ground vertebrates are consumed when encountered in leaf litter and soil ( Kingdon 1979, 1997; Whitesides 1985; Blake and Fay 1997; Grubb et al. 1998; Harris and Cerling 2002; Beaune et al. 2012; Leus and Vercammen 2013). Foraging style of P. porcus involves “[continuous] probing of the leaf litter and soil with the [large, disk-shaped] nose” (Leus and Vercammen 2013:38) and scraping the soil with tusks and forefeet ( Happold 1987). In moist earth, the bridge of the nose (rather than the tip of snout) is used to overturn soil (Leus and MacDonald 1997). Rooting is often the most prominent field sign of P. porcus ( Happold 1987) ; in lowland rainforests of Taï National Park, Côte d’Ivoire, 24% ± 16.4 SE of quadrats showed soil disturbance by foraging P. porcus ( Dunham 2011) .

Digestion coefficients for captive P. porcus fed a diet of concentrate pellets, produce, grains, and egg were reported by Clauss et al. (2008); of note was the higher digestion rate of hemicellulose compared with cellulose. Described as a mixed-feeder in Ituri Forest, Democratic Republic of the Congo, isotopic analyses of tooth enamel suggested that P. porcus obtains most of its food from gap and clearing vegetation ( Cerling et al. 2004) and functions as a browsing omnivore (Harris and Cerling 2002). Beaune et al. (2012:509) described P. porcus as “the largest member of the granivore guild” in Salonga National Park, Democratic Republic of the Congo, where foraging groups of 2–6 individuals ate fruits and seeds from 26 tree and 2 liana species of 14 families (species of Sapotaceae and Caesalpiniaceae were most often eaten). Particular preference for drupes from the palm Elaeis and fruits from Irvingia gabonensis , Coula edulis, Baionnella toxisperma, and Chrysophyllum was reported by Malbrant and Maclatchy (1949). P. porcus opened and ate 54% ± 3 SE of seeds in the fall zone of 54 bush mango trees ( Irvingia gabonensis ) in Salonga National Park, Democratic Republic of Congo; a limited sample of feces did not contain whole seeds suggesting that seed consumption by P. porcus was predaceous and did not result in seed dispersal (Beaune et al 2012). Abernethy and White (1999) reported similar efficient seed predation in Lopé National Park, Gabon, except for Uapaca seeds that germinate in old feces. Methane production from methanogenic bacteria in feces of P. porcus averages 34 CH 4 nmol g−1 h−1 (Hackstein and van Alen 1996).

Sounds from a group of P. porcus crunching seeds in their powerful jaws have been described as “explosive” and can be heard as far away as several hundred meters (Abernethy and White 1999). In a swampy Congolese forest clearing (“bai”) frequented by African forest elephants, several groups of P. porcus and western sitatunga ( Tragelaphus gratus ) regularly ate nuts from elephant dung (video at http://www.arkive.org/red-river-hog/potamochoerus-porcus/video-00.html); P. porcus spent 33% of its feeding time in the clearing eating from the dung, mostly consuming nuts of Panda oleosa (Pandaceae) , Strombosia pustulata (Olacaceae) , and Strychnos camptoneura ( Loganiaceae — Magliocca et al. 2003).

Potamochoerus porcus can be an agricultural pest, with a particular fondness for cassava, yams, and cocoyams ( Bates 1905; Grubb et al. 1998; Ayeni et al. 2001). An early account of a captive male P. porcus , raised at a mission in southern Cameroon, noted its carnivorous habits; this individual became proficient at catching and eating domestic chickens, behavior that led to his demise and a place on the dinner table ( Bates 1905). P. porcus at the Duisburg Zoo, Germany, actively killed neonatal sheep and goats that shared the same enclosure, and several zoos have reported female P. porcus cannibalizing their own young ( Gewalt 1988). In the wild, there are anecdotal reports of groups scavenging carcasses ( Turkalo 2010); Abernethy and White (1999:53) recounted seeing “20 red river hogs quite literally crammed inside the dead body of an elephant that poachers had recently killed.”

Diseases and parasites. —Knowledge of diseases and parasites of Potamochoerus porcus in the wild is limited. African swine fever is a viral hemorrhagic fever of great concern to the domestic pig industry in Africa and more recently Europe, South America, and the Caribbean because it results in 100% morbidity and up to 100% mortality in domestic pigs (Jori and Bastos 2009; Costard et al. 2013). African swine fever is caused by a DNA virus in the family Asfarviridae and seems to be most commonly transmitted by soft ticks in the Ornithodoros moubata complex ( Vial et al. 2007; Costard et al. 2013). In Africa, the putative vertebrate host of African swine fever is the common warthog, and African swine fever has been widely reported in its populations (e.g., Anderson et al. 1998; Jori and Bastos 2009; Costard et al. 2013); P. porcus is also a likely vector ( Vercammen et al. 1993; Leus and Vercammen 2013). Although it is sometimes difficult to distinguish which Potamochoerus species was studied (Jori and Bastos 2009), outbreaks of African swine fever specific to P. porcus have been reported in Nigeria ( Luther et al. 2007; Owolodun et al. 2011).

Potamochoerus porcus has many of the same genomic signatures of porcine endogenous retroviruses in its DNA that are found in other Old World suids; these signatures represent the “remains of ancient retroviral infection events…[surviving] as part of the host genome rather than as an infectious agent” ( Patience et al. 2001:2771). Postweaning multisystemic wasting syndrome—a disease that was 1st diagnosed in the domestic pig industry in the North Hemisphere in the 1990s, with “pathological features associated with porcine cirovirus type 2”—killed a captive juvenile female P. porcus in the United Kingdom; the female died 2 weeks after the syndrome was 1st recognized, despite treatment with trimethoprim and sulfadiazine (Woodger and Hosegood 2011:512). Although not confirmed by serology, 10 mortality events involving at least 64 carcasses of P. porcus were suspected to be associated with outbreaks of Ebola hemorrhagic fever in Gabon and the Democratic Republic of Congo from November 1994 to April 2005 ( Lahm et al. 2007).

Potamochoerus porcus is an “alleged” vector for trypanosomiasis and an intermediate host of trichinosis ( Vercammen et al. 1993; Leus and Vercammen 2013:40). A single captive male P. porcus at the University of Ibadan Zoological Garden, Nigeria, was infected with the helminth Ascaris lumbricoides , a parasite with human-health implications ( Ajibade et al. 2010). Recent studies in the wild show that many ticks ( Ixodidae ) are common on P. porcus . Specimens of P. porcus collected in savanna, semideciduous forest, and coastal areas in Ghana harbored the ticks Rhipicephalus cuspidatus , R. lunulatus , R. simpsoni , R. ziemanni , and Ixodes cumulatimpunctatus ( Ntiamoa-Baidu et al. 2005) . In the Central African Republic, the ticks Amblyomma paulopunctatum , Rhipicephalus aurantiacus , R. complanatus , R. longus , R. lunulatus , R. muhsamae , and R. ziemanni were found on P. porcus ( Uilenberg et al. 2013) . Myiasis sinusitis caused by developing larvae from the oestrid fly Rhinoestrus nivarleti occurs in P. porcus in Gabon ( Payne 2005).

Interspecific interactions. —Leopards ( Panthera pardus ) prey on Potamochoerus porcus where they co-occur ( Hayward et al. 2006). In Lopé National Park, Gabon, P. porcus was found in 20.4% of 80 leopard scats during the dry season (June–September) and 25% of 73 scats during the rainy season (October–December), and it was the most important prey item relative to biomass: 19.7% of the total biomass consumed ( Henschel et al. 2005; Henschel 2008). In a broader study in Gabon, encompassing Lopé and Ivindo national parks and surrounding areas, P. porcus occurred in 16.2– 36.7% of 180 leopard scats—2nd only to duikers ( Cephalophini — Henschel et al. 2011). Hart et al. (1996) found P. porcus in 13.1% of 222 leopard scats in Réserve de Faune à Okapis, Ituri Forest, Democratic Republic of the Congo. P. porcus also was found in 3 leopard “hairballs” and 5 scats in Salonga National Park, Democratic Republic of Congo ( D’Amour et al. 2006). In northern Cameroon, lions ( Panthera leo ) prey on P. porcus , which constitutes 6.9% of the diet during the November–April dry season ( Breuer 2005). Although chimpanzees ( Pan troglodytes ) are known to prey on P. larvatus in East Africa ( Goodall 1963), specific documentation of them preying on P. porcus is lacking; they co-occur in West Africa (Russak and McGrew 2008) and occasional predation of young is likely ( Alp 1993; Abernethy and White 1999). Other predators include pythons, eagles, and spotted hyenas ( Crocuta crocuta — Kingdon 1997; Leus and Vercammen 2013).

Potamochoerus porcus probably competes for food and space with some sympatric ungulate herbivores within its distribution. Regarding other suids, P. porcus and 2 species of forest hogs ( Hylochoerus rimator and H. ivoriensis ) share much of the same distribution in west-central Africa (Groves and Grubb 2011). These species of forest hogs also need areas that provide permanent water and have a thick understory for shelter, but in contrast to P. porcus , they prefer grassland–forest ecotones, eat predominantly grasses and fruits, have greater tolerances for cold temperature, and can be found at higher elevations ( Kingdon 1979, 1997; Meijaard et al. 2011). Forest hogs are known to “chase off other herbivores from choice pastures” ( Kingdon 1979:188), and because they likely usurp preferred sleeping areas and perhaps nesting sites, P. porcus is uncommon where forest hogs are abundant ( Estes 1991; Meijaard et al. 2011). P. porcus and the common warthog can be sympatric in extreme northern Central African Republic and Democratic Republic of the Congo near the borders of Chad and South Sudan, but they vary greatly in their habitat preferences, with the warthog preferring “treeless open plains and lightly wooded savannas” (Leus and Vercammen 2013:38). P. larvatus and P. porcus are allopatric ( Grubb 1993b; Leus and Vercammen 2013).

Given the new ungulate taxonomy of Groves and Grubb (2011), P. porcus could co-occur with as many as 22 duikers (6 species of Philantomba and 16 species of Cephalophus — Huffman 2011). Forest duikers are primarily frugivorous ( Huffman 2011) and show some dietary overlap with P. porcus . Evidence provided by camera traps deployed in Central African rainforests suggest that P. porcus , duikers, and other mammal species partition their use of forest clearings throughout the day and night, thereby minimizing direct competition; for example, 3 species of Cephalophus used the clearings, on average, from 10:15 to 11:31 h, in contrast to peak use at 19:23 h by P. porcus ( Gessner et al. 2013) .

Figures

Fig. 1.—Mature male Potamochoerus porcus in Gabon, West Africa. Note the characteristic white dorsal crest, long white whiskers, spectacled black-and-white facemask, and elongated leaf-shaped ears with terminally dropping tufts of hair. Photograph by B. Huffman.

Fig. 2.—Early depiction of Potamochoerus porcus, the “painted pig of the Cameroons,” highlighting the rufous coat, white dorsal mane, and elongated, leaf-shaped ears (Gray 1854:280, plate XXXIV).

Fig. 3.―Male Potamochoerus porcus develop cone-shaped protuberances on either side of the muzzle that serve to protect tendons along the nose during male-to-male interactions. They are just visible in a 14-month-old juvenile male (top) but become prominent in a 5-year-old mature male (bottom). Photographs by B. Huffman.

Fig. 4.—Current and possible distribution of Potamochoerus porcus in equatorial Africa.

Fig. 5.—Dorsal, ventral, and lateral views of skull and lateral view of mandible of an adult male Potamochoerus porcus (USNM [United States National Museum] 220144), collected by C. R. Aschemeier in “Fr[ench]. Congo [= presently Gabon, Republic of the Congo, and Central African Republic], Ntyonga [presently southern Gabon, presumably Nyanga Province]” on 2 March 1918. Note dried remnants of the nasal snout (not included in length of skull measurement) and bony canine apophysis, growing upwardly posterior to the upper canines. Greatest length of skull is 346.9mm.

Fig. 6.—Neonatal Potamochoerus porcus has a distinctive pattern of yellowish longitudinal stripes and spots (top; 2 weeks old) that fade to red at about 6 months after birth. Juveniles (bottom; about 9 months old) can be distinguished by the lack of both the stripes of infants and prominent facial markings of adults. Photographs by B. Huffman.

Fig. 7.—Potamochoerus porcus tends to prefer damp forest habitat. Thick vegetation is used as cover, especially at midday (top). Foraging occurs in open and grassy clearings (bottom) primarily from dusk until dawn. Photographs by B. Huffman.