376

Chapter

34

A Genomic Perspective on Wild Boar

Demography and Evolution

Marcel Amills, Hendrik-Jan Megens, Arianna Manunza, Sebastián E. Ramos-Onsins, and

Martien A. M. Groenen

A Genomic Perspective on the Evolutionary

History of Sus Speciation

Pig-like species (Suidae) are found in many different parts

of the world. This superfamily consists of at least 15 different

extant species found in Africa, South America, Europe, and Asia

(Table 34.1). Suid species in Eurasia exhibit a striking dichot-

omy in their distribution. While there are at least seven recog-

nized suid species on Island South East Asia (ISEA), only two

are found on the Eurasian mainland (Table 34.1). Even in these

two species on the Eurasian mainland, the dichotomy could not

have been starker: one species, the pygmy hog (Porcula salvania)

is confined to a relatively small region in the north of India and

south of Nepal, where it relies on a rather special ecosystem,

i.e. the grasslands near the southern foothills of the Himalayas.

The pygmy hog was recently proposed to be reassigned to a sep-

arate genus relative to the genus Sus (Funk et al. 2007). On the

other hand, Sus scrofa, the other Eurasian mainland species, can

be found throughout this largest landmass on our planet, when-

ever woodlands or shrubs are present, and snow cover in winter

is not too prolonged. Although wild boar certainly has a defined

ecology, its wide range does exemplify the opportunistic nature

of this species.

It has long been recognized that suiformes in the Americas

(peccaries; Tayassuidae) form a distinct group compared to the

Old World pigs (Suidae). This has recently been confirmed by

population genomics approaches that put a date for the diver-

gence between these two groups in the Oligocene (around

27–34 Ma: Frantz 2015; Frantz et al. 2016, see also Figure 34.1).

Within the Old World suids, the oldest divergence time lies

in the middle to late Miocene (8–13 Ma), when Babyrousa of

Sulawesi radiated from all other Suidae (Frantz 2015; Frantz

et  al. 2016). Divergence between the African suids and the

genus Sus appears to have taken place around the late Miocene

or at the very beginning of the Pliocene, around 10–6 Ma

(Frantz 2015; Frantz et al. 2016). The importance of this finding

lies in the fact that phylogenetic analyses confirm paleontologi-

cal data indicating that pigs were present throughout most of

Eurasia in the Plio- and Pleistocene. Yet, Sus scrofa appears to

be a more recent, albeit basal, offshoot of a group of suid spe-

cies that make up the genus Sus (Frantz et al. 2013). The other

clade, in contrast, gave rise to at least six species, mostly con-

fined to ISEA. What this highlights is a contrast in the modes

of divergence within these two major suid clades, the Eurasian

Mainland (EAM) and ISEA.

Divergence between these two main branches in the genus

Sus is thought to coincide with the late Pliocene, or the very early

stages of the Pleistocene. Cooling of the Earth in the past 50 million

years culminated in the ice-age cycles of the Pleistocene, thus low-

ering the sea levels and exposing large parts of the Sunda plateau.

This circumstance may have facilitated migration from EAM to

ISEA, and vice versa. Even while some of the islands never became

connected by land, it is likely that the lowering of sea levels resulted

in the shrinking of sea barriers to a degree that it became feasible

for pigs to cross them occasionally. It is very likely that Sulawesi

and the Philippines were colonized in this way.

Suid species in ISEA are mostly confined to single islands

or island groups. For instance, Sus verrucosus distribution is

mainly circumscribed to Java, Sus celebensis to Sulawesi, and

Sus cebifrons to a few neighbouring islands in the Philippines.

Table 34.1 Geographic distribution of pig-like species (Suidae).

Common name Latin name Geographic

location

Wild boar Sus scrofa Mainland Europe and

Asia, Sumatra

Bearded pig Sus barbatus Borneo, Sumatra,

Malay Peninsula

Javan warty pig Sus verrucosus Java, Bawean

Celebes warty pig Sus celebensis Sulawesi

Visayan warty pig Sus cebifrons Philippines (Negros,

Panay)

Philippine warty pig Sus philippensis Philippines

Pygmy hog Porcula salvania India (Assam)

Moluccan babirusa Babyrousa babyrussa Sulawesi (Moluccan

region)

Common warthog Phacochoerus

africanus

Africa

Desert warthog Phacochoerus

aethiopicus

Africa

Bushpig Potamochoerus

larvatus

Africa

Red river hog Potamochoerus porcus Africa

Collared peccary Pecari tajacu North, Central and

South America

White-lipped peccary Tayassu pecari Central and South

America

Chacoan peccary Catagonus wagneri South America

.036

12:55:56

http://www.ebook3000.com