Nubian ibex
Male
Female
Conservation status
Vulnerable  (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Family:	Bovidae
Subfamily:	Caprinae
Tribe:	Caprini
Genus:	Capra
Species:	C. nubiana
Binomial name
Capra nubiana F. Cuvier, 1825[2]

The Nubian ibex (Capra nubiana) is a desert-dwelling goat species (Genus Capra) found in mountainous areas of northern and northeast Africa, and the Middle East.^[2] It was historically considered to be a subspecies of the Alpine ibex (C. ibex), but is now considered a distinct species. The wild population is estimated at 4,500 mature individuals, and it is classified as vulnerable.^[1]

Taxonomy

Fossil history

The earliest remains of Nubian ibex in Israel date back approximately 150,000 years to the Pleistocene, and they have been continually present in the region since this time.^[3][4] In spite of the growing presence of livestock like domesticated goats over the last 10,000 years, Nubian ibex in the region have remained present throughout this time.^[5] However, their abundance has fluctuated over time in places like Ein Gedi, where they showed an increase in population in the Late Holocene between 949 and 5,164 years ago.^[6] Radiocarbon dated bones from archaeological excavations indicate that the Nubian ibex has been in a predator-prey relationship with the Arabian leopard throughout the Holocene.^[7]

Phylogeny

The Nubian ibex shares a genus, Capra, with all other ibex and goats. Phylogenetic reconstructions of the ibex/goat family tree have mixed results, with different studies reaching different conclusions.

One Y-chromosomal DNA analysis suggests two clades (subgroups) within the genus: The first clade contains domestic goats (C. hircus), bezoars (Capra aegagrus), and markhors (C. falconeri). The second clade contains all other ibex, including the Nubian ibex. In this analysis, the Nubian ibex is monophyletic (most closely related) to the Siberian ibex (C. sibirica).^[8]

However, when the same study analyzed Mitochondrial DNA, it was suggested that all species in genus Capra are in one clade except for the Siberian ibex. The study's authors provide potential explanations for this discrepancy, including a possible ancient hybridization of the ancestors of the two Y-chromosome clades.^[8]

A separate mitochondrial study suggests that the Nubian ibex forms a separate, more ancient offshoot from most other ibex and may be monophyletic with the Siberian ibex.^[9]

An additional Y-chromosomal DNA and mitochondrial DNA study concludes that Nubian ibex are most closely related to Ethiopia's Walia ibex (C. walie), and they may have separated about 800,000 years ago.^[10]

Another study used multidimensional scaling (MDS) to suggest that Nubian ibex are more closely related to Alpine ibex and European ibex than to all others.^[11]

Genetic analysis suggests that their population was relatively high during the last interglacial period, and decreased during the last ice age.^[12] The genetic makeup of Nubian ibex as a species has remained unchanged for at least 2,000 years.^[13] There is genetic evidence of ancient gene introgression between Nubian ibex and bezoar ibex, which, in turn, interbred with domestic goats and left genetic signatures.^[14]

The following cladogram of seven Capra species is based on 2022 mitochondrial evidence:^[15]

Description

Nubian ibex are the smallest ibex species on Earth, following Bergmann's rule. They stand around 65–75 cm (26–30 in) tall at the shoulder. They are sexually dimorphic: males are significantly larger than females, with males averaging 52–74.7 kg (115–165 lb) and females 25.3–32.7 kg (56–72 lb).^[3][16]

They are a light tan color, with a white underbelly; males also have a dark brown mane down their backs. Their legs have a black and white pattern. They have a lighter rump with a dark brown tail. Males begin growing a beard at age 2 or 3, which continues to grow longer and darker as they age. During the autumn breeding season, mature males grow a "rutting fur" on their breast and sides which is very dark brown. It appears in October in 3–4-year-old males, but it may appear as early as July or August in older males age 6 and up. However, not all males develop rutting fur, even at a mature age.^[3]

Nubian ibexes have long, thin horns that extend up and then backwards and down. In males, these reach around 1 m (3 ft 3 in) in length, while in females they are much smaller, reaching around 30 cm (12 in).^[17] Male horns are thicker than female horns, and grow large bulges which prevent the horns from sliding while the males are locked in combat.^[3] Male horn growth plateaus around age 7–8, where as female horn growth plateaus around age 4–6. There is a significant relationship between the individual's age and the number of horn ridges.^[18]

Distribution

Historically, Nubian ibex were distributed across the Middle East and Northeastern Africa.^[1] Its range today is within Egypt, Jordan, Oman, Israel, Palestine, Saudi Arabia and Sudan.^[1] It was extirpated in Lebanon, though a captive breeding and reintroduction process is underway.^[19] It has also been extirpated in Syria.^[20] Its presence is uncertain in Ethiopia, Eritrea and Yemen.^[1]

Ecology and behavior

Feeding

Nubian ibex live in rough, dry, mountainous terrain, where they eat mainly grasses and leaves, especially from Acacia trees (Genus Vachellia). They forage for food on the ground and may also rear up on their hind legs to reach leaves in trees. They can climb into trees while feeding.^[3] They reduce feeding on plants with strong defenses, such as tannins and thorns.^[21] Preferred plants vary depending on the amount of rain; rainy winters result in higher feeding preference for annual plants over perennials.^[22] Ibex preferentially feed in spaces that are close to cliffs where they can easily escape predators, demonstrating a Landscape of Fear: the farther from cliffs, the more vigilant ibex become.^[23][24] Ibex will also spend more time feeding in green patches with high nutritional quality and that are closer to water sources.^[25][26] Female Nubian ibex in Oman have been recorded consuming small bone fragments (osteophagy), a common behavior in mammals to supplement calcium and phosphorus in their diet.^[27]

Ecological relationships

They are preyed upon by Arabian leopards (Panthera pardus nimr),^[28][29] Arabian wolves (Canis lupus arabs),^[30][31] golden jackals (Canis aureus),^[32] caracals (Caracal caracal),^[33] red foxes (Vulpes vulpes), golden eagles (Aquila chrysaetos),^[34] Eurasian eagle owls (Bubo bubo),^[34] and bearded vultures (Gypaetus barbatus).^[35] When alarmed, they emit a shrill call to alert other ibex of danger. They share their habitat with numerous other herbivores, including rock hyrax (Procavia capensis), Arabian oryx (Oryx leucoryx), gazelles (Genus gazella), and Asiatic wild ass (Equus hemionus).^[3] Nubian ibex have a mutualistic relationship with Tristram's starling (Onycognathus tristrumil), a small bird that eats the parasites on the ibex's skin.^[36]

They may host parasites including: the ibex fly (Lipoptena chalcomelanea), blood sucking lice (Linognathus africanus and Damalinia sp.), ticks (Hyalomma rhipicephaloides, Boophilus annulatus, and others), mites (Psoroptes cuniculi and Sarcoptes scabiei), and biting flies (Oestrus sp.) and fleas.^[3][37] They have also been found with brain cysts caused by the parasite Taenia multiceps.^[38]

Disease

Nubian ibex have been detected with a strain of the malignant catarrhal fever (MCF) virus group of ruminant rhadinoviruses, closely related to caprine herpesvirus 2 (CpHV-2) found in domestic goats.^[39] Nubian ibex in Qatar's Al Wabra Wildlife Preservation have been infected by caprine pleuropneumonia.^[40][41] In Jerusalem’s Biblical Zoo, the Nubian ibex herd suffered an outbreak of peste des petits ruminants.^[42]

Social behavior

Ibex are social, and herds tend to consist of females, young, and males up to the age of about three years. Herds are typically up to 20 individuals, but may reach as high as 50. Female herds are often composed of related individuals that follow a dominance hierarchy.^[3][43][16] The males are solitary or form more transitory bands of up to eight individuals. During the breeding season, males join the female-based herds for the six- to eight-week rut. Large males then do battle with much clashing of horns.^[17]

Movement

Nubian ibexes are diurnal, meaning they are active during the day, and rest at night. Like other ibex and goats, Nubian ibex spend much of their time on and around cliffs, which offer safety from potential predators. Ibex perceive a greater predation risk as they move farther away from cliffs.^[24] They climb and leap with ease, spanning several meters horizontally and vertically in a single leap. Ibex typically traverse cliffs in single file when possible, and keeping relatively horizontal. Their repeated movement over time creates well-worn hillside trails.^[3]

Ibex migrate throughout the day and throughout the year. During the day, they navigate between food patches as they forage. They may rest throughout the day to chew their cud, especially around midday.^[3] Additionally, on cold winter days, ibex in Egypt have been documented following the path of the sun each day to stay warm.^[44] At night, they sleep on cliff sides in small depressions that they dig. These shallow diggings create microhabitats where a diverse range of seedlings can germinate, adding to the habitat's diversity.^[45] In winter and early spring, the Middle East's rainy season, ibex often disperse to open plateaus where they can feed on new plant life. In the hot, dry summer, they congregate around shaded oases with water and greenery.^[3]

Reproduction and life history

Mating season is typically in October and November, during which a dominant male will pursue several females. Males produce a strong scented secretion when females are in estrous. As they pursue potential mates, they smell the females' anal region with lip curled up (Flehmen). Males can reach breeding maturity as young as 2 years, but may not be allowed to mate until age 5 when they are strong enough to fend off rival males. Females can breed as young as six months old, but often don't breed until age 1-3.^[3] Studies suggest that some Nubian ibex subpopulations are developing a second mating season in the spring, in response to hyper-arid climates.^[33]

Gestation lasts 5 months. Litters of 1-2 kids are born between March and July, although the majority of births are synchronized in a 3-4 week period that peaks in late March and April. Females leave the herd to give birth in a secluded space. Newborns can stand within 15 minutes of birth, and can nurse within two hours. The mother and young rejoin the herd in a few days, joining other mothers and young to form a crèche for several weeks.^[3] Leaving kids in a sheltered crèche allows mothers to seek out richer food patches and spaces that are farther from cliffs, compared to mothers that keep their kids with them at all times.^[46] Kids are weaned around 4 months old. Females reach mature size at age 3-4, while males reach it around 6 years old. Nubian ibex can live up to 12 years in the wild and 18 years in captivity.^[3]

Physiology

Eyes and vision

Nubian ibex vision is adapted to navigating visually on mountainous terrain. A study of their retinal ganglion cell density shows that they share many traits with other artiodactyls: a temporal area, horizontal streak, and dorsotemporal extension. They have a potentially unique dorsotemporal area of high ganglion cell density that benefits vision in the lower visual field, helpful for navigating varied terrain. Additionally, they have a more loosely organized horizontal streak than other hoofed animals. Their tapetum lucidum is morphologically similar to that of goats. It is blue-green, and enhances their night vision and vision of the horizon. The spatial resolving power in their temporal area is 17 cycles/degree, meaning that they can distinguish objects as small as 3 mm (0.12 in) from a distance of up to 30 metres (98 ft), allowing for food identification and predator detection.^[47] The Nubian ibex's standard intraocular pressure is estimated to be 17.95 ± 4.78 mmHg.^[48] They produce relatively low rates of tears compared to other animal species, leaving them highly susceptible to infection.^[49]

Blood composition

Nubian ibex can balance their body's nitrogen levels on poor quality diets by reabsorbing large quantities of their bodies' urea.^[50] This slows their metabolism when only poor quality food is available, but Nubian ibex can regain lost body mass rapidly upon returning to a higher quality diet.^[51] Nubian ibex and other desert-dwelling ungulates have elevated isotopes of Nitrogen (δ¹⁵N) due to their diet of plants that grow in denitrified soils.^[52]

Most hematological, serum biochemical, and electrolyte values are consistent between males and females. However, females have significantly higher red blood cell counts, hematocrit, total leucocyte (white blood cell) counts, and total serum bilirubin than males.^[53]

Genetic adaptations to the desert

Genetic analyses identify 22 positively selected genes in Nubian ibex, when compared to domestic goats (Capra hircus). The genes affect such functions as immune response, protein ubiquitination, olfactory transduction, and visual development. 3 of the genes have evolved to develop skin barriers that mitigate solar radiation in the hot desert.^[54] They also have copy number variations (CNVs) of genes associated with xenobiotic metabolism and energy metabolism, due to processing desert plants with many secondary metabolites.^[55] Additional solar radiation mitigation adaptations include genes associated with hair follicle development and increased DNA repair mechanisms. Nubian ibex also have CNVs for expanded toxic compound removal, to deal with more toxic foods than other goat species eat.^[56]

Yaez (Nubian ibex x domestic goat hybrid) physiology studies