|Wild gerbil in Mongolia|
Meriones unguiculatus, the Mongolian jird or Mongolian gerbil is a rodent belonging to subfamily Gerbillinae. It is the most widely known species of the gerbil subfamily, and is the usual gerbil species to be kept as a pet or experimental animal, when it is known as the domesticated gerbil. Like the Syrian or golden hamster, it was first brought to the United States in 1954 by Dr. Victor Schwentker for use in research. Forty-four pairs were caught in Mongolia and brought to England. They were described as "squirrel colors... with long furry tails." They are somewhat larger than mice, with a body about 12 cm long (and a tail of similar length), with body mass averaging 50-55 grams in females and 60 grams in males.
Meriones unguiculatus evolved on the semideserts and steppes of Mongolia. There, they developed long legs for jumping and running from predators, teeth to deal with hard seeds and plant matter, and water conservation techniques that allow them to survive in the arid climate, such as the ability to use dry food or stores of fat to generate metabolic water. Mongolian gerbils do not have many natural enemies due to the harsh climate. Most predators are birds of prey or snakes. Mongolian gerbils are diurnal, but return to their burrows for the coldest and hottest parts of the day.
The species M. unguiculatus came originally from Mongolia. Its habitat there is mainly semideserts and steppes. Soil on the steppes is sandy and is covered with grasses, herbs, and shrubs. The steppes have cool, dry winters and hot summers. The temperature can get up to 50 °C (122 °F), but the average temperature for most of the year is around 20 °C (68 °F).
In the wild, these gerbils live in groups generally consisting of one parental pair, the most recent litter, and a few older pups. Only the dominant female will produce pups, but she will mate with multiple males while in estrus (heat). One group of gerbils generally ranges over 325–1,550 square metres (0.08–0.38 acres).
A group lives in a central burrow with 10–20 exits. Some deeper burrows with only one to three exits in their territory may exist. These deeper burrows are used to escape from predators when they are too far from the central burrow. A group's burrows often interconnect with other groups.
The first known mention of gerbils came in 1866, by Father Armand David, who sent "yellow rats" to the Museum of Natural History (Musée d'Histoire Naturelle) in Paris, from northern China. They were named Meriones unguiculatus by the scientist Milne-Edwards in 1867. This scientific name in a combination of Greek and modified Latin loosely translates as "clawed warrior" in English, partly stemming from the Greek warrior Meriones in Homer's Iliad, combined with 'unguiculate' meaning to have claws or nails.
Gerbils only became popular pets after 1954, when 20 breeding pairs were brought to the United States from eastern Mongolia for scientific testing. Almost all pet gerbils today are descended from these 40. Gerbils were brought to the United Kingdom in 1964 from the United States.
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The Mongolian gerbil has become an important research animal for several reasons. In the wild during the long, cold winter of the arid and semi-arid regions of Mongolia, China and Russia the gerbil stays in small social groups mostly underground in a series of burrows in which separate areas are designated for food storage, sleeping, and voiding. The enclosed living habitats of domestication is similar and gerbils easily adapted to the new setting. In addition gerbils are able to manufacture most vitamins in their metabolic system so fresh vs. dehydrated foods are not a requirement for their health, and indeed can give them diarrhea. The extra dry environment this produces in their living areas keeps the growth of bacteria and fungi down and keeps odours down too. This means they are very easy animals to keep in a research setting.
About 50% of Mongolian gerbils also display an epileptic faint when under stress which might serve as a way to play dead in the wild. This characteristic has proven very useful to researchers of epilepsy and related illnesses.
During meiosis male Mongolian gerbils do not interchange reciprocal alleles between pairs of homologous chromosomes ("chiasmata" or "Crossing Over"), a trait very rare in eutherian mammals and indeed animals in general. Meiotic recombination occurs in females alone.
While gerbils are intelligent and social animals, they have not performed as well as rats at intelligence tests based on a maze pattern because they prefer to explore a new environment thoroughly rather than go straight to the food reward. Their curiosity is apparently greater than their desire to eat.
The Mongolian gerbil, a gentle and hardy animal, has become a popular pet. It was first brought from China to Paris, France in the 19th century, and became a popular house pet. It was then brought to the United States in 1954 by Dr. Victor Schwentker for use in research. Selective breeding for the pet trade has resulted in a wide range of different color and pattern varieties.
Mongolian gerbils prefer to live in pairs or groups rather than alone. They are social and gentle, and do not bite readily. As diggers and tunnel-makers they are better suited to a tank with a deep substrate rather than a hamster cage, since the absorbent substrate is liable to be kicked up and out of a cage pretty quickly. Gerbils are also chewers and need plenty of cardboard items and chew toys. Cardboard will be chewed up into bedding and mixed with the substrate. Gerbils do not need fresh food and indeed it can give them diarrhea, a diet based on a seed, millet and alfalfa pellet mix is sufficient. Water should be provided in a drip-feed system to prevent the accidental build-up of harmful molds in the tank environment. Although gerbils are desert-adapted, they do require water to be supplied at all times. Care should be taken not to introduce new smells suddenly into the tank, which is considered by the gerbils to be their territory. Gerbils are active and appreciate a running or exercise wheel. Repetitive corner digging can be minimized by providing tunnels while gerbils are in their formative months. As with most animals, they appreciate a secure, private area that is dark for sleeping.
Currently recognized colour morphs and their genetic basis are described below.
- Golden Agouti — All Mongolian Gerbils in the wild are Golden Agouti, also called Agouti. The hair shafts on the back are grey at the base, gold in the middle and tipped with black, making an even mix of golden brown with black ticking. The belly is creamy white. An Agouti gerbil has black eyes.
- Black — A Black gerbil is black both on its back and on its belly. It most often has a "bib" or white line running down its chin. It also may have some white on its paws. A Black gerbil has black eyes. It carries double recessive genes abbreviated "a" for Agouti.
- Argente / Argente Golden — An Argente gerbil is orange with a creamy white belly. It has deep ruby eyes. If one were to brush back the fur on its back, one would see that the roots are grey. Argente gerbils carry double recessive genes for "Pink Eyed" which is abbreviated, "p" although the eye colour is ruby rather than pink.
- Argente Cream — An Argente Cream gerbil is an Argente lightened by a Himalayan gene, c(h). It is light orange with a creamy white belly and ruby eyes. The undercoat is grey like the Argente Golden, but diluted due to the c(h).
- Topaz — A Topaz gerbil is an Argente lightened by a gene called Chinchilla Medium, c(chm), formerly called Burmese, c(b). This colour is lighter than an Argente Golden but darker than an Argente Cream, and it often has slightly darker points at the ears, nose and tail. It has a creamy white belly and ruby eyes. The undercoat is grey, but diluted due to the c(chm). Also called "Argente Fawn."
- Lilac — A Lilac gerbil is medium grey all over. It has ruby eyes and carries double recessives for both the "a" and "p" alleles.
- Dove — A Dove gerbil is a Lilac lightened by the Himalayan gene, c(h). It is light grey all over. It has ruby eyes.
- Sapphire — A Sapphire gerbil is a Lilac lightened by a gene called Chinchilla Medium, c(chm). This colour is lighter than a Lilac but darker than a Dove. It has ruby eyes.
- Pink-eyed White — A Pink-eyed White gerbil is completely white with pink eyes.
- Himalayan/Dark Tailed White — A Himalayan or Dark Tailed White gerbil is white with ruby eyes. After several months its tail will darken from white to a shade of light or dark grey depending on a variety of factors such as the temperature of the environment and the other recessive alleles it may carry. A gerbil that is Dark Tailed White, abbreviated "DTW," carries double recessives of the Himalayan gene, "c(h)."
- Burmese — A Burmese gerbil is an all over chocolate colour. Around eight weeks or so, it will begin to develop darker points on the tail, nose, feet and tips of the ear. It often has a "bib" or white line running down the chin. It also may have some white on its paws. All Burmese gerbils have black eyes with a pupil which reflects red in bright light. It is also known as a "Colourpoint Black" and carries double recessives for "a" as well as "c(chm)" alleles.
- Siamese — A Siamese gerbil starts out a light mushroom colour. Around eight weeks, it moults and the tail, nose, feet and tips of the ear go black. The main body colour stays the same. A Siamese has black eyes with a pupil which reflects red in bright light. It also often has a "bib" or white line running down the chin. It may also have some white on the paws.Younger Siamese gerbils can have lighter bands on their feet, but will fade on the back but may stay on the front. Their colour is also described as "Mushroom Colourpoint" or "Light Colourpoint Black" and they carry double recessives of the "a" allele, as well as one c(chm) and one c(h) allele.
- Colourpoint Agouti — A Colourpoint Agouti gerbil has an off-white to grey base with a liberal amount of silvery-brownish ticking along the back. The tail is a ticked light gold and claws are black. The belly is white and the eyes are black with a pupil which reflects red in bright light. Also called simply "Colourpoint," sometimes abbreviated, "CPT." It carries double recessives of the "c(chm)" allele.
- Light Colourpoint Agouti — A Light Colourpoint Agouti has an off-white base with silvery-brownish ticking along the back and dark claws. Its belly is white and its eyes are black with a pupil which reflects red in bright light. Also called "Light Colourpoint," sometimes abbreviated, "LCPT." It carries one "c(chm)" allele and one "c(h)" allele.
- Grey Agouti — The hairs on the back of a Grey Agouti are dark grey with white in the middle, making an even salt-and-pepper look. They often have gold intermingled into the coat. The belly is white and claws are dark. A Grey Agouti has eyes which are black with a pupil which reflects red in bright light. It carries double recessives of the Underwhite dense gene, "uw(d)." This gene was formerly thought to be the Grey allele, "g."
- Pearl — A Pearl gerbil, also called a "Colourpoint Grey Agouti" is a Colourpoint Agouti gerbil which carries double recessives for the "uw(d)" allele. It is a salt and pepper ticked grey gerbil with no gold colour on the tail and very even ticking all over. The ticking is less pronounced than on a Grey Agouti coat. It has black eyes with a pupil which reflects red in bright light and has grey or beige claws.
- Slate — A Slate gerbil is a greyish black colour. Often has a "bib" or white line running down the chin. It may also have some white on the paws. It has grey claws. A Slate has black eyes with a pupil which reflects red in bright light. It carries double recessives of the "a" as well as the "uw(d)" alleles.
- Ivory Cream — An Ivory Cream gerbil is cream or very pale yellow on its back with a lighter creamy white belly. It has ruby eyes. It is also called "White-bellied Cream" or "Ivory." It carries double recessives of the "p" as well as the "uw(d)" alleles.
- Red-Eyed White — A Red-Eyed White gerbil is white all over. It has ruby eyes. Also known as Ruby Eyed White and abbreviated as "REW." It carries double recessives of the "a," "p" and "uw(d)" alleles.
- Satin — a Satin gerbil is a light cream colour with a marked sheen and ruby eyes which darken with age. It has a white undercoat. It carries double recessives of the Underwhite gene, "uw."
- Azure Slate — An Azure Slate gerbil is dark grey with black eyes. It carries double recessive genes for "a" as well as one Underwhite allele and one Underwhite Dense allele.
- Dark Eyed Honey — A Dark Eyed Honey gerbil starts out with a bright orange back with a white belly and flanks. At eight weeks old it moults and a small amount of black ticking appears along its back. It carries double recessives of the "Extension of Yellow" gene, notated "e." A Dark Eyed Honey has black eyes. Dark Eyed Honey is often abbreviated as "DEH."
- Nutmeg — A Nutmeg gerbil starts out with a bright orange colour over its entire body. At eight weeks old it moults and liberal black ticking appears along the back with a lesser amount on the belly, changing the colour from an orange to a rich ticked brown, depending on the extensiveness of the ticking. The normal moulting process may give this gerbil type a brindled appearance at times. A Nutmeg gerbil has black eyes. Nutmeg gerbils carry double recessives of the "a" and "e" alleles.
- Silver Nutmeg — A Silver Nutmeg gerbil's first coat is an ivory or light peach colour. At eight weeks old the gerbil moults and the liberal greyish ticking appears along the back with a lesser amount on the belly. A Silver Nutmeg gerbil has black eyes with a pupil which reflects red in bright light and has dark claws. Silver Nutmegs carry double recessives of Underwhite Dense, "uw(d)" and Extension of Yellow, "e" as well as "a" alleles.
- Red Eyed Honey — A Red Eyed Honey gerbil has a bright orange back with a white belly and flanks. It has ruby eyes. It is also known as a "Yellow Fox." Red Eyed Honey is often abbreviated as "REH." Red Eyed Honey gerbils carry double recessives of "e" and "p" alleles.
- Saffron — A Saffron gerbil is a bright orange colour over its entire body, with the colour lightening somewhat through the belly area. Often there is a "bib" or white line running down the chin. There may also be some white on the paws. A Saffron gerbil has ruby eyes. It is also known as a "Red Fox." Saffron gerbils carry double recessives of "a" as well as "p" and "e" alleles.
- Polar Fox — A Polar Fox starts out an ivory or light peach colour. At eight weeks old the gerbil moults and minimal greyish ticking appears along the back. The claws are clear. A Polar Fox has black eyes with a pupil which reflects red in bright light. A Polar Fox gerbil carries double recessives of the "e" and "uw(d)" alleles.
- Schimmel — A Schimmel gerbil starts out as an orange colour. At eight weeks old it moults and the back begins to lighten to a creamy white. The gerbil's body continues to lighten throughout its life until it can be left with a creamy white body, while the tail, nose, feet and tips of the ears retain the orange. Schimmel gerbils have black eyes. A Schimmel gerbil carries double recessives of the Schimmel gene, notated as "e(f)." A Schimmel with ruby eyes due to carrying double "p" recessive alleles is a Red Eyed Schimmel, also called a Ruby Eyed Schimmel.
- Blue — A Blue gerbil is a dark grey colour, sometimes with very faint ticking. It's pigment is slightly lighter on the tail, ears and paws. It has black eyes. It carries double recessives of the Dilute gene, abbreviated, "d."
- Smoke — A Smoke coloured gerbil is a medium to dark grey colour with dark eyes. It carries double recessives for both "d" and "uw(d)" alleles.
- Black Eyed White — A Black Eyed White gerbil is completely white with black eyes. Some have greyish ear tips and dark claws. Black Eyed White gerbils are often the result of combining many different recessive genes—for example, a Light Colourpoint Dark Eyed Honey, "LCP DEH" which carries double recessives of the "e" alleles as well as a "c(h)" and a "c(chm)" allele, but always retaining a dominant gene for Pink Eyed, "P." The only exceptions would be if double recessives of the Himalayan gene or the Underwhite gene are present, which will turn a Pink Eyed dominant gerbil's eyes to ruby.
- Spotting - Dominant spotting can be in any coat variety and will lighten the fur around it. How the spotting will look depends on modifiers. The claws of a spotted gerbil are a pale colour. Spotting types that don't conform to show standards are usually classed as patched. Spotting is notated as "Sp."
- Collared - A thick, unbroken band of spotting around the neck connecting to the white belly.
- Collar and blaze - A thick, unbroken band of spotting around the neck connecting to the white belly and an unbroken white blaze connecting the three spotting areas (neck, forehead and nose).
- Pied - The base coat colour may be of any standard type except for white. There is a thick band of white around the neck and shoulder area to form a collar that is connected to a blazed down the forehead and face. The distinguishing feature are small spots on the rump and back area around the spinal area. These spots usually do not have clear edges. The gerbil may be 50% white before it is considered a mottled gerbil as long as the spotting pattern conforms to the standard, accepted pattern.
- Mottled - The coat colour of the gerbil may be any standard coat colour broken by small white patches accompanying a collar and blaze. The gerbil may be up to 75% white until it would be considered a variegated gerbil.
- Variegated - The variegated pattern is when any standard coat colour is broken up by small white patches along with a collar and blaze. The difference between the variegated spotting form and the mottled spotting form is the amount of white. The variegated spotting is an extended form of mottling. There is more white on the back and rump, allowing less colour to show through. This can form a "dalmatian" pattern. Often the tail tuft and the end of the tail is white or lacking pigment.
- Extreme White - The extreme white pattern is associated with any standard colour except for white. Here the coat colour is 90% white and barely any of the base coat colour, or any pigment, is remaining. There have been health concerns circulating about extreme white gerbils. Head tilts, lack of good balance, and repetitive running and circling has been reported in these gerbils. It has been found that these health concerns mostly affect gerbils with unpigmented (light pink/not very opaque) ears.
- Dark Patched Pied/Spotted — When a somatic reversion mutation causes a dark spot of the original, unlightened fur to appear on a spotted gerbil, it is called Dark Patched Pied. This trait does not conform to standard Mendelian inheritance patterns though certain lineages are more prone to produce it.
Note: Although some gerbil owners call some coat varieties "Fox," for example Yellow Fox, the fox gene is not in gerbils which is misleading.
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Though not much is known about breeding in wild Mongolian gerbils, we know that they can have as many as 18 pups, compared to pet gerbils which can only have 14. The families make sure all young females in their groups leave before that can fall pregnant and kill the mothers' newer pups whilst still in the family unit. The father or older brothers will mate with younger females. These young females have the ability to carry sperm for up to 2 weeks until they are sexually mature (at 3–4 months) so that they can make a family of their own without the interference of another male who may kill the fathers pups. This is why it isn't recommended to keep an older male gerbil with a younger female as a cage mate for a prolonged amount of time.
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