158.

Great Gerbil

Rhombomys opimus

French: Gerbille géante / German: Riesenrennmaus / Spanish: Gerbillo grande

Taxonomy. Meriones opimus Lichtenstein, 1823,

Karakumy Desert, Kzyl-Ordinskaya, Kazakhstan.

Originally described as a member of genus Meriones, R. opimus was later considered the sole representative of a new genus Rhombomys created by J. A. Wagner 1841 on basis of its unique dental characters. Many authors agreed with this distinction, including I. Ya. Pavlinov and colleagues in their 1990 tribe revision. In a molecular analysis in 2010, M. Ito and coworkers found R. opimus to be sister taxon of Brachiones przewalskii, both being in same clade as Psammomys obesus; there appears to be no close relationship between current Meriones and R. opimus, thus validating Wagner's new genus. M. A. Oshaghi et al. in 2011 found a high molecular variability within Iranian populations. Chromosomes were studied by M. B. Qumsiyeh and D. A. Schlitter in 1991. Monotypic.

Distribution. Kazakhstan, Uzbekistan, Turkmenistan, Iran, Kyrgyzstan, Tajikistan, N Afghanistan, SW Pakistan (Balochistan), N China (Xinjiang, Gansu, Inner Mongolia [= Nei Mongol], and Ningxia), and S Mongolia.

Descriptive notes. Head—body 150-185 mm, tail 130-160 mm, ear 12-19 mm, hindfoot 36-47 mm; weight 169-275 g. The Great Gerbil is one of the largest jirds and is characterized by relatively short tail (around same as head-body length or shorter). Dorsal pelage is ocherous to gray and ventral one dull white. Tail is bicolored and ends with a pencil of black hairs. This species is characterized by presence of ever-growing hypsodont and rootless molars which cementum in re-entrant angles. Karyotype is 2n = 40.

Habitat. Sandy or clay deserts, with a local preference for dry riverbeds and shrubby vegetation.

Food and Feeding. Diet is based on high plant diversity. It includes stems,leaves, and branches of small bushes, especially Haloxylon ammodendron ( Amaranthaceae), or succulent bushes such as Salsola (Amaranthaceae) . Diet varies seasonally,depending on plant availability. For instance, chenopods are eaten more in autumn and winter, Cyperaceae in spring, and Compositae in summer. Highest diversity of plants in the diet is reached in spring.

Breeding. Reproduction occurs throughout year, with a reduction in summer. Litter size is 1-14 (average 4-7).

Activity patterns. Diurnal, and most active at dawn. Great Gerbils are terrestrial, digging very elaborate burrow systems with long, deep tunnels, nest chambers, and foraging chambers. In winter the nest may be situated 2-5 m below the surface.

Movements, Home range and Social organization. In Uzbekistan, Great Gerbils are not very social and form small family groups consisting of one male and six females. The groups are flexible and are able to adjust their territories to unpredictable climatic and environmental conditions. When food is limited females are generally solitary, and when conditions are better they share their territory with other females of the same family group (philopatry). Males mark their burrows with urine, feces and ventral-gland secretions, and chase other males; they seem to adjust to the distribution of the females. Reproduction and litter sizes are dependent onrainfall and food availability. When a predator (snake, fox, mustelid) appears, three different alarm vocalizations have been described for the Great Gerbil and these seem to act as alert signals, used to communicate to the group information about a danger:first is a rhythmic repetition of a single note, then a faster and more intense call, and then a single whistle. In all cases the gerbils adopt a quadrupedal or bipedal alert posture and stop feeding and moving. The first signal is emitted when predatoris farthest away, and the two others when it is closer; short single-note whistle indicates closest presence of predator, and individual gerbils run into burrows. Hindfoot drumming in reaction to alarm vocalizations have been reported.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Great Gerbil is abundant, and its behavior and ecology have been well studied. In some regions,this rodent causes damage to the vegetation and is considered a pest.

Bibliography. Ito et al. (2010), Liu Wei et al. (2012), Oshaghi et al. (2011), Pavlinov et al. (1990), Qumsiyeh & Schlitter (1991), Randall & Rogovin (2002), Randall, Rogovin, Parker & Eimes (2005), Randall, Rogovin & Shier (2000), Smith & Yan Xie (2008), Wagner (1841).