Mongolian gerbil

The Mongolian gerbil or Mongolian jird (Meriones unguiculatus) is a small rodent belonging to the subfamily Gerbillinae.[2] Body size is typically 110–135mm, with a 95–120mm tail, and body weight 60–130g, with adult males larger than females.[3] The animal is used in science and kept as a small house pet. Their use in science dates back to the latter half of the 19th century, but they only started to be kept as pets in the English-speaking world after 1954, when they were brought to the United States. However, their use in scientific research has fallen out of favor.

"Gerbil" redirects here. For other uses, see Gerbil (disambiguation).
"Pet gerbil" redirects here. For other gerbil species, see Gerbillinae.

Mongolian gerbil
Wild gerbil in Mongolia
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Muridae
Genus: Meriones
Species:
M. unguiculatus
Binomial name
Meriones unguiculatus
Wilhelma Zoo, Stuttgart, Germany

Habitat

Mongolian gerbils inhabit grassland, shrubland and desert, including semidesert and steppes in China, Mongolia, and the Russian Federation.[4]

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 patriarchal groups generally consisting of one parental pair, the most recent litter, and a few older pups, sometimes the dominant female's sister(s) also live with them. Only the dominant females will produce pups, they will mate only with the dominant male while in estrus (heat), female gerbils are generally more loyal than male gerbils. 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.

History

The first known mention of gerbils came in 1866, by Father Armand David, who sent "yellow rats" to the French National Museum of Natural History in Paris, from northern China. They were named Meriones unguiculatus by the scientist Henri Milne-Edwards in 1867.

There is a popular misconception about the meaning of this scientific name, appearing both in printed works[5] and in websites,[6] due to the genus Meriones sharing the name with Greek warrior Meriones in Homer's Iliad; however, translations like "clawed warrior" are incorrect. The genus was named by Johann Karl Wilhelm Illiger in 1811,[7] deriving from the Greek word μηρος (femur). Combined with 'unguiculate', meaning to have claws or nails in Latin, the name can be loosely translated as 'clawed femur'.[8]

Gerbils only became popular pets in the English-speaking world after 1954, when 20 males and 26 females were brought to the United States from eastern Mongolia for scientific testing. Almost all pet gerbils today are descended from them. Gerbils were brought to the United Kingdom in 1964 from the United States.

In science

Gerbils have a long history of use in scientific research, although nowadays they are rarely used. For example, in the United Kingdom in 2017, only around 300 Mongolian gerbils were used in experimental procedures, compared to over 2 million mice.[9]

Tumblebrook Farm

Most gerbils used in scientific research are derived from the Tumblebrook Farm strain, which has its origins in 20 pairs of wild-caught Mongolian gerbils sent to Japan in 1935. 11 of these animals were subsequently sent to Tumblebrook Farm in the USA, with additional animals later sent to Charles River Ltd in Italy in 1996.[10][11][12]

Hearing

Gerbils have a wide hearing range, from detection of low frequency foot drumming to higher frequency chirps and therefore may be a more suitable model of human hearing loss than mice and rats, which are high-frequency specialists.[13]

Vocal

Male gerbils can produce ultrasonic sounds with frequencies ranging from approximately 27 to 35 kHz and amplitudes ranging from approximately 0 to 70 dB. Their larynx is involved in the production of these ultrasonic sounds. Experimentation revealed five findings of interest, which are that adults only emit ultrasonic sounds when stimulated socially, males signal frequently than females, dominant males are active in vocalizations than subordinate males, ultrasounds are triggered by conspecific odors, and d-amphetamine, a central nervous system stimulant, contributes high levels of ultrasounds and chlorpromazine, an antipsychotic medication, lowers the emission rate. In addition, there's been a relationship between the ultrasonic sounds and their ability to reproduce.[14]

Epilepsy

10–20% of gerbils exhibit spontaneous epileptiform seizures, typically in response to a stressor such as handling or cage cleaning.[15] Epilepsy in gerbils has a genetic basis, and seizure-prone and seizure-resistant lines have been bred.[16][17]

Diabetes

Like other desert rodents such as fat sandrats, Mongolian gerbils are susceptible to diet-induced diabetes, although incidence is low.[18] A diabetes-prone line has recently been generated, showing that gerbil diabetes has at least some genetic basis.[19][20]

Genetics and genomics

Laboratory gerbils are derived from a small number of founders, and so genetic diversity was generally assumed to be low. Initial genetic studies based on small numbers of genetic markers appeared to support this,[21][22] but more recent genome-wide Genotyping-by-Sequencing (GBS) data has shown that genetic diversity is actually quite high.[10] It has been suggested that laboratory gerbils should be considered domesticated, and designated "M. unguiculatus forma domestica" to differentiate them from wild animals.[23] A Mongolian gerbil genome sequence was published in 2018[24] and a genetic map comprising 22 linkage groups (one per chromosome) in 2019.[25]

Reproduction
Mongolian Gerbil Young

These rodents are widely used as subjects of testing within laboratories for a plethora of different reasons.[26] These rodents are susceptible to carrying diseases and infections some transmitted sexually, much the subject of many experiments within labs.[27] In the wild, Wild Mongolian gerbils breed during the months of February and October. Males do not become sexually mature for about 70–80 days, while the vaginal opening occurs in females about 33–50 days after birth.[28] For other gerbils such as the hairy footed gerbil, sexual maturity has a slightly earlier and longer window of 60-90[29] days in comparison with a later and shorter window for Mongolian gerbils, 70–84 days.[28] Females reach sexual maturity shortly after this opening occurs. They experience oestrus cycles every 4–6 days. Mongolian gerbils are regarded as monogamous within science.[30] Even with this said, many Mongolian Gerbils have still been found in laboratory tests regarding their sexual reproduction behavior to have shown signs of "cheating" when not in contact with their initial mate in laboratory setting.[30] Cheating meaning showing signs of promiscuity and mating with other females while their monogamous partner is absent. Gerbils are for the most part selective when it comes to picking a mate for copulation; though their selection process occurs more rapid than other species due to the high amount of gerbil population and shorter life span. An average litter size for the Mongilian Gerbil would be around 4–8 pups, if the litter only contains around 1–2 young than the mother will neglect them and they will die from starvation.[30] Mongolian Gerbils are monogamous and mate with their selected partner for the rest of their time together, when one becomes widowed many gerbils refrain from seeking other mates to reproduce with.[30] Males generally find new mates whereas females don't. Obviously not every single gerbil is going to act the same after losing their mate but for the most part these rodents do not seek additional partners after the fact. When older females lose their mate they almost all of the time give up on seeking reproduction.[30] Their behavior tends to vary when faced with different settings, within the wild finding and selecting a mate is not a problem at all due to the high frequency of mates. Within a laboratory setting many gerbils tend to keep to themselves and refrain from copulation.[30]

Behavior

Gerbils are social animals, and live in groups in the wild.[31] They rely on their sense of smell to identify other members of their clan, so it is important to use what is commonly referred to as the "split tank method" (or splitcaging) when introducing gerbils from separate litters.[32] Gerbils are known to attack and often kill those carrying an unfamiliar scent.[33]

As pets

Pet gerbils eating millet

A gentle and hardy animal, the Mongolian gerbil has become a popular small house pet. It was first brought from China to Paris in the 19th century, and became a popular house pet there.[34] It was later brought to the United States in 1954 by Dr. Victor Schwentker for use in research.[35] Dr. Schwentker soon recognized their potential as pet animals.[36] Selective breeding for the pet trade has resulted in a wide range of different color and pattern varieties.[37] Gerbils became popular pets in the US around the late 1950s and were imported to the United Kingdom in 1964, where they became popular pets too.[38] They are now found in pet shops throughout the UK and the US.

However, due to the threat they pose to indigenous ecosystems and existing agricultural operations, it is illegal to purchase, import, or keep a gerbil as a pet in the U.S. state of California.[39] It is also illegal to import the animal into New Zealand.


Housing in captivity

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 or bedding rather than a hamster cage, since the absorbent substrate is liable to be kicked up and out of a cage quickly.

Mongolian gerbils are also chewers and need plenty of cardboard items and chew toys; the cardboard will be chewed up into the bedding and mixed with the substrate. They do not need fresh food like vegetables and it can actually give them diarrhea; a diet based on one or more seeds, millet and alfalfa pellet mix is sufficient.

Water should be provided with a drip-feed system to prevent an accidental build-up of harmful molds in the tank environment. Although gerbils are adapted to the desert, they require water to be supplied at all times to be safe and healthy. Care should be taken not to introduce new smells suddenly into the tank, because the tank 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 young, formative months. As with most animals, they appreciate a secure, private area that is dark for sleeping.[40]

A common misunderstanding when purchasing a home for pet gerbils is they can live in housing designed for hamsters and mice. This is not correct, as they need to be able to dig tunnel systems, rather than have them created for them. The commonly plastic structure of hamster and mouse cages is inappropriate for gerbils due to their ability to gnaw through it very quickly. Plastic can cause serious health issues for the animal if ingested, therefore many owners refrain from having any plastic in the tank and rely entirely on wooden toys.[41] Information from gerbil societies from throughout the globe is conflicting with regards to tank sizing. However, a common minimum given appears to be 45 litres (10 imperial gallons) per gerbil.[41]

Mating

Gerbils will mate for several hours, in frequent short bursts followed by short chases, when the female allows the male to catch her. Once he catches her, the female will squeak and make flick motions to get the male off her. Males will not attack females except in rare circumstances, which may also include them having been separated from their original mates, or widowed. A female may attack a male, but usually he is more than a match for her.

Reasons for popularity

The several reasons for the popularity of gerbils as household pets include: The animals are typically not aggressive, and they rarely bite unprovoked or without stress. They are small and easy to handle, since they are sociable creatures that enjoy the company of humans and other gerbils.[42][43] Gerbils also have adapted their kidneys to produce a minimum of waste to conserve body fluids, which makes them very clean with little odor.

Teeth problems

Misalignment of incisors due to injury or malnutrition may result in overgrowth, which can cause injury to the roof of the mouth. Symptoms include a dropped or loss of appetite, drooling, weight loss, or foul breath.[44] The teeth must be clipped by a veterinarian regularly for as long as required.

Trauma

Common injuries are caused by gerbils being dropped or falling, often while inside of a hamster ball, which can cause broken limbs or a fractured spine (for which there is no cure).[44][45]

Neglect

A common problem for all small rodents is neglect, which can cause the gerbils to not receive adequate food and water, causing serious health concerns, including dehydration, starvation, stomach ulcers, eating of bedding material, and cannibalism.[44]

Epilepsy

Between 20 and 50% of all pet gerbils have the seizure disorder epilepsy.[46] The seizures are thought to be caused by fright, handling, or a new environment. The attacks can be mild to severe, but do not typically appear to have any long-term effects, except for rare cases where death results from very severe seizures.[47] A way to prevent a gerbil from having a seizure is to refrain from blowing in the animal's face (often used to "train" the pet not to bite). This technique is used in a lab environment to induce seizures for medical research.[48]

Tumors

Tumors, both benign and malignant, are fairly common in pet gerbils, and are most common in females over the age of two. Usually, the tumors involve the ovaries, causing an extended abdomen, or the skin, with tumors most often developing around the ears, feet, midabdomen, and base of the tail, appearing as a lump or abscess.[47] The scent gland (positioned on the abdomen) should be checked regularly; a veterinarian can operate on the lump where possible.[49]

Tail sloughing

Gerbils can lose their tails due to improper handling, being attacked by another animal, or getting their tails stuck. The first sign is a loss of fur from the tip of the tail, then, the skinless tail dies off and sloughs, with the stump usually healing without complications.[47]

Tyzzer's disease

The most common infectious disease in gerbils is Tyzzer's disease, a bacterial disease, which stress can make animals more susceptible to. It produces symptoms such as ruffled fur, lethargy, hunched posture, poor appetite, diarrhoea, and often death. It quickly spreads between gerbils in close contact.[47]

Deafness and inner ear problems

A problem with the inner ear can be spotted by a gerbil leaning to one side quite obviously. The fluids in the ears affect balance. However, this does not appear to affect the gerbils too much, which have an attitude of just getting on with things, and getting used to their conditions. Gerbils with "extreme white spotting" colouring are susceptible to deafness; this is thought to be due to the lack of pigmentation in and around the ear.[50]

Captive-bred gerbils
A Burmese colored gerbil
A male and female fat-tailed gerbil (Pachyuromys duprasi)

Many color varieties of gerbils are available in pet shops today, generally the result of years of selective breeding.

Over 20 different coat colors occur in the Mongolian gerbil, which has been captive-bred the longest.[51]

Another species of gerbil has also been recently introduced to the pet industry: the fat-tailed gerbil, or duprasi. They are smaller than the common Mongolian gerbils, and have long, soft coats and short, fat tails, appearing more like a hamster. The variation on the normal duprasi coat is more gray in color, which may be a mutation, or it may be the result of hybrids between the Egyptian and Algerian subspecies of duprasi.[52][53]

White spotting has been reported in not only the Mongolian gerbil, but also the pallid gerbil[54] and possibly Sundervall's Jird.[55]

A long-haired mutation, a grey agouti or chinchilla mutation, white spotting, and possibly a dilute mutation have also appeared in Shaw's jirds,[56] and white spotting and a dilute mutation have shown up in bushy-tailed jirds.[57]

Coat colours

Currently recognized colour morphs and their genetic basis are described below.[58]

Golden Agouti
Lilac
Dove
Burmese
Light Colourpoint Agouti
Nutmeg
Silver Nutmeg
Schimmels
  • 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 brown. 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. Its 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).
Mottled black
  • 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: some coat varieties, for example Yellow Fox, are described as fox strains despite not carrying the fox gene

References
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