Subfamily Myospalacinae
zokors

The subfamily Myospalacinae, the zokors, is an Old World group of fossorial muroid rodents. There are six species belonging to two genera in this subfamily, Myospalax and Eospalax. (Musser and Carleton, 2005)

Myospalacines are distributed throughout China and southern Siberia. (Nevo, 1999)

Myospalacines are found in woodlands, steppes, river valley meadows, pastures, old agricultural fields, and vegetable gardens. They are most common at elevations between 900 and 2,120 meters. (Carleton and Musser, 1984; Nevo, 1999; Nowak, 1999)

Over the years, there has been confusion about where exactly the subfamily Myospalacinae belongs. Zokors have been placed with the families Muridae (Alston 1876, Thomas 1896, Ellerman 1940, 1941, Musser and Carleton 1993), Spalacidae (Tullberg 1899, Miller and Gidley 1918), and Cricetidae (Simpson 1945, Chaline et al. 1977). Based on skull characteristics, Lawrence (1991) argued that myospalacines belong in a group basal to other muroid rodents, and that any similarities with cricetids are independently evolved. Recently, molecular evidence has either pointed to cricetines (Michaux et al. 2001) or to spalacines and rhizomyines (Jansa and Weksler 2004, Norris et al. 2004) as the nearest relatives of zokors. The hypothesis that myospalacines are spalacids along with rhizomyines, spalacines, and tachyoryctines currently has the most support, and is the taxonomy represented here.

There has also been confusion about the relationships among the species within Myospalacinae. Lawrence (1991) recognized seven zokor species, which she classified within a single genus, Myospalax. She divided this genus into four species groups, three of which have living members. Her classification was based mostly on skull characteristics. Musser and Carleton (2005), have retained the groupings of Lawrence (1991), except that they have combined her groups 1 and 2 into the genus Myospalax and assigned the genus Eospalax to her group 4. A molecular phylogeny of Myospalacinae proved inconclusive, but two species--Myospalax aspalax and Myospalax psilurus--did consistently fall in a clade basal to the other five Myospalax species recognized in the study (Norris et al. 2004). (Alston, 1876; Carleton and Musser, 1984; Chaline, Mein, and Petter, 1977; Ellerman, 1940; Ellerman, 1941; Jansa and Weksler, 2004; Lawrence, 1991; Michaux, Reyes, and Catzeflis, 2001; Miller and Gidley, 1918; Musser and Carleton, 1993; Musser and Carleton, 2005; Norris et al., 2004; Simpson, 1945; Thomas, 1896; Tullberg, 1899)

Myospalacines have long, cylindrical bodies. They have soft, thick, gray to buff-colored fur, with a smattering of short vibrissae on the head. The body's ventral surface is usually paler than the dorsal surface. The tail is short; head and body length ranges from 147 to 270 mm and tail length ranges from 29 to 96 mm. Zokors weigh between 150 and 563 grams. The eyes are tiny and covered by fur and there are no external ears. The limbs are short, but the feet are very wide and strong, with curved claws. The third claw on each forefoot is the strongest, whereas the 1st and 5th digits are reduced. The longest claws on the forefeet are at least three times the length of the claws on the hindfeet.

The myospalacine dental formula is 1/1, 0/0, 0/0, 3/3 = 16. The incisors are orthodont, and the molars are hypsodont and omegaform. Myospalacines have tympanic bullae that are somewhat inflated and their mallei are perpendicular in conformation. They have fused cervical vertebrae, stomachs composed of three parts, and 16-chambered ceca. There are three pairs of mammae. Myospalacines have a diploid number of chromosomes between 44 and 64. (Carleton and Musser, 1984; Nevo, 1999)

The lifespan of myospalacines has not been reported.

Myospalacines spend almost all of their time below ground, burrowing about through the soil. They dig with their forefeet and push out soil with their heads. If forced to walk above ground, they curve their long foreclaws down under their feet and walk on top of them. Each zokor constructs a burrow system consisting of a nest chamber, storage chamger, and defecation chamber about two meters below the surface, with one to four shallower foraging tunnels radiating outward. These foraging tunnels may be up to 100 meters long. When zokors dig, they push loose earth out of their tunnels and onto the soil surface, leaving a series of dirt mounds in their wake. Zokors occasionally forage above ground at night. They are active throughout the year, but their activity peaks in the spring and the fall. Zokors are mainly solitary, and can be highly aggressive and territorial. (Li, Wang, and Zhao, 2003; Nevo, 1999; Nowak, 1999)

Zokors have keen senses of smell and hearing. Their eyes, although small, are sensitive to light. They communicate with one another by scent-marking with their urine and feces. They also have particular calls they use when threatening or attacking other individuals, and they give an alarm squeal when threatened by predators. (Li et al., 2000; Li, Wang, and Zhao, 2003; Nevo, 1999; Nowak, 1999)

Myospalacines are primarily herbivores. Bulbs, roots, grains, and rhizomes make up the bulk of the zokor diet, but they also eat leaves and shoots, and occasionally, insects and other arthropods. Zokors dig underground storage chambers where they keep surplus plant foods for future consumption. (Ganzorig et al., 1999; Nevo, 1999; Nowak, 1999)

Many species of mammalian carnivores, hawks, eagles, and owls prey upon zokors. A few of the species that include zokors in their diet are: steppe polecats (Mustela eversmanii), Eurasian ferrets (Mustela nigripes), Chinese mountain cats (Felis bieti), Pallas’s cat (Felis manul), Eurasian lynx (Lynx lynx), foxes (Vulpes ferrilata and V. vulpes), golden eagles (Aquila chrysaetos), upland buzzards (Buteo hemilasius), saker falcons (Falco cherrug), goshawks (Accipiter gentilis), black kites (Milvus migrans), and little owls (Athene noctua). Zokors probably avoid much predation by spending most of their time underground and only coming above ground to forage at night. (Zhang, Zhang, and Liu, 2003)

Zokors may increase plant diversity and change the competitive interactions among plants in the short term by creating a heterogeneous distribution of nutrients when they deposit soil on the ground surface. They also may aerate soil and allow water to reach plant roots more easily. However, in the long run, they have been shown to decrease the biomass of certain types of plants and thus lower the plant species diversity overall. They negatively impact plant growth not only by consuming plants but through their burrowing activity, which disturbs or destroys plant roots. An indirect benefit of zokors is that they avoid eating plants that contain secondary chemical compounds, so those plants tend to become dominant and prevent livestock from overgrazing. The activities of zokors affect other animals, too. Many species of birds, mammals, reptiles, and amphibians seek refuge and breed in zokor burrows. Zokors compete with other small mammals for space. And finally, a range of predatory mammals and birds, as well as a number of parasites (including nematodes, fleas, ticks, and mites), depend on zokors as a food source. (Ganzorig et al., 1999; Litvinov and Sapegina, 2003; Zhang, Liu, and Du, 2004; Zhang, Zhang, and Liu, 2003)

When present in large numbers, zokors can become serious agricultural pests, destroying crops, competing with cattle for browse, and causing soil erosion. For these reasons, intensive poisoning campaigns have been carried out by local governments in China since the 1980s. (Zhang, Zhang, and Liu, 2003)

Since the 1970s, zokor bones have been used in place of tiger bones in traditional Chinese medicine. (Zhang, Zhang, and Liu, 2003; Zhou, Zhou, and Zhang, 2004)

The IUCN lists three myospalacine species as lower risk (Myospalax psilurus, M. rothschildi, M. smithii), and one as vulnerable (M. fontanierii). Eradication campaigns and harvesting of zokors for their bones have taken their toll on zokor populations. Recently, scientists have acknowledged that "pest" species such as zokors only become problematic when rangeland is overgrazed, and they recognize that native wildlife is essential for preserving a balanced ecosystem. Therefore, comprehensive rangeland management plans that seek to preserve the natural equilibrium and do away with the widespread practice of killing zokors have now been adopted by landowners throughout western China. (IUCN, 2004; Zhang, Zhang, and Liu, 2003)