Spalax

Spalax Temporal range: Early Miocene–Recent PreЄ Є O S D C P T J K Pg N
Spalax ehrenbergi
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Superfamily:	Muroidea
Family:	Spalacidae
Subfamily:	Spalacinae Gray, 1821
Genus:	Spalax Guldenstaedt, 1770
Species
Spalax antiquus Spalax arenarius Spalax carmeli Spalax ehrenbergi Spalax galili Spalax giganteus Spalax golani Spalax graecus Spalax istricus Spalax judaei Spalax leucodon Spalax microphthalmus Spalax munzuri Spalax nehringi Spalax uralensis Spalax zemni
Synonyms
Nannospalax Palmer, 1903

The genus Spalax contains the blind, fossorial, or subterranean mole-rats, which are one of several types of rodents that are called mole-rats.^[1] The hystricognath mole-rats of the family Bathyergidae are completely unrelated, but some other forms are also in the family Spalacidae. Zokors (subfamily Myospalacinae) and root rats and bamboo rats (subfamily Rhizomyinae) are spalacids sometimes referred to as mole-rats. Blind mole-rats are in the family Spalacidae, but are unique enough to be given a separate subfamily, Spalacinae. Alternate opinions on taxonomy consider the blind mole-rats to be the only members of the family Spalacidae and rank other spalacid subfamilies as full families. Other authors group all members of the superfamily Muroidea into a single family, Muridae. The Spalacinae contains two genera and eight species. Some authorities treat all species as belonging to a single genus, Spalax.

Spalax mole-rats are truly blind.^[2] Their very small eyes are completely covered by a layer of skin. Unlike many other fossorial rodents, Spalax mole-rats do not have enlarged front claws and do not appear to use their forearms as a primary digging tool. Digging is almost exclusively conducted using their powerful front teeth, which are separated from the rest of the mouth by a flap of skin. When a Spalax mole-rat closes its mouth, its incisors are still on the outside. Blind mole-rats may have evolved from spalacids that used their front limbs to dig, because their olecranon processes are relatively large relative to the rest of their arms. The olecranon process is a part of the ulna bone where muscles attach, and digging animals tend to have enlarged olecranon processes to provide a large surface for their large and powerful muscles to attach.

Because they are completely blind, blind mole-rats have been important laboratory animals in tests on how eyes and eye proteins function.

Resistance to cancer

Studies on the growth of fibroblasts in vitro of Spalax judaei and Spalax golani showed that the process of necrosis replaces the role of the systematic apoptosis normally used in most organisms. Low-oxygen conditions, such as those common in blind mole-rats’ burrows, usually cause cells to undergo apoptosis. In adaptation to higher tendency of cell death, blind mole-rats evolved a mutation in the tumor suppressor protein p53 (which is also used in humans) to prevent cells from undergoing apoptosis. Human cancer patients have similar mutations, and blind mole-rats were thought to be more susceptible to cancer because their cells cannot undergo apoptosis. However, after a specific amount of time (within 3 days according to one study), the cells in blind mole-rats release interferon-beta (which the immune system normally uses to counter viruses) in response to overproliferation of cells caused by the suppression of apoptosis. In this case, the interferon-beta triggers cells to undergo necrosis, and this mechanism also kills cancer cells in blind mole-rats. Because of tumor suppression mechanisms such as this, blind mole-rats and other spalacids are resistant to cancer.^[3][4][5]

Classification

Subfamily Spalacinae

• Genus Spalax – Blind mole-rats
  • Spalax antiquus^[6]
  • Sandy mole-rat, Spalax arenarius
  • Mount Carmel blind mole-rat, Spalax carmeli
  • Middle East blind mole-rat, Spalax ehrenbergi
  • Upper Galilee Mountains blind mole-rat, Spalax galili
  • Giant mole-rat, Spalax giganteus
  • Golan Heights blind mole-rat, Spalax golani
  • Balkan mole rat, Spalax graecus
  • Spalax istricus^[7]
  • Judean Mountains blind mole-rat, Spalax judaei
  • Lesser mole-rat, Spalax leucodon
  • Greater mole-rat, Spalax microphthalmus
  • Munzur mole-rat, Spalax munzuri
  • Nehring's blind mole-rat, Spalax nehringi
  • Kazakhstan blind mole-rat, Spalax uralensis
  • Podolsk mole-rat, Spalax zemni

References

Further reading

• Jansa, S. A. and M. Weksler (2004). Phylogeny of muroid rodents: relationships within and among major lineages as determined by IRBP gene sequences. Molecular Phylogenetics and Evolution, 31:256–76. doi:10.1016/j.ympev.2003.07.002 PMID 15019624
• Michaux, J., A. Reyes, and F. Catzeflis (2001). "Evolutionary history of the most speciose mammals: molecular phylogeny of muroid rodents." Molecular Biology and Evolution, 17:280–293.
• Musser, G. G. and M. D. Carleton (2005). "Superfamily Muroidea." pp. 894–1531 in Wilson, D. E. and D. M. Reeder, eds. Mammal Species of the World: a Taxonomic and Geographic Reference. 3rd ed. Baltimore: Johns Hopkins University Press.
• Norris, R. W., K. Y. Zhou, C. Q. Zhou, G. Yang, C. W. Kilpatrick, and R. L. Honeycutt (2004). "The phylogenetic position of the zokors (Myospalacinae) and comments on the families of muroids (Rodentia)." Molecular Phylogenetics and Evolution, 31:972–978.
• Nowak, R. M. (1999). Walker's Mammals of the World, II. London: Johns Hopkins University Press ISBN 978-0-8018-5789-8
• Steppan, S. J., R. A. Adkins, and J. Anderson (2004). Phylogeny and divergence date estimates of rapid radiations in muroid rodents based on multiple nuclear genes. Systematic Biology, 53:533–553. doi:10.1080/10635150490468701 PMID 15371245
• Topachevskii, V. A. (1976) Fauna of the USSR. Volume III: Mammals. Issue 3: Mole rats, Spalacidae. New Delhi: Amerind.