Degu Appearance

Here you'll find out what degus look like in detail. Click the buttons to view pictures as you read. For those of you without easy access to a furry friend, this is the place to be! For those of you who think you know it all, think again- you have much to learn...

>OVERVIEW<
Degus are medium-sized³² diurnal crepuscular rodents²¹, despite being one of the smallest caviomorphs to inhabit South America⁵¹. They have five clawed toes on each of their and five on their ^{30, 52}. Each digit is well developed, apart from the fifth digit which is reduced⁵². The nails on the hind feet are curved⁵¹ and covered with long, comb-like stiff bristles^{51, 52}. They have a 'moderately long'⁵² (shorter than the head and body) with a small black brush at the tip^{51, 52}. The is short and soft⁵², and is lighter towards the belly (see below). Degus have 20 teeth^{52, 57}; two pairs of incisor teeth^{52, 57}, two pairs of premolars⁵² and six pairs of molars^{57, 52}. Degu are high-crowned⁵² and ever-growing, consistent with eating fibrous plant matter in the wild⁵¹. The molars have only moderate indentation⁵² (whereas other species have deep molar indentation⁵²). The is orange⁵² (see below). The are well developed and of a moderate size⁵². Ears are darkly pigmented with little fur⁵², but the ear canal is protected by long, slightly coarser . The ears are shaped to capture sound and to dissipate body heat. Degus have large, dark surrounded by a ring of light fur⁵², positioned on the side of the head to improve the range of vision. There is sometimes a of light fur around the sides of the neck⁵². The is hairless, small and usually dark in appearance, although there are . Just behind the nose are a series of , which vary in length depending on the size of the degu. Whiskers are a sensory mechanism and are very sensitive to touch stimuli. are also present to allow the degu to determine both the width and height of a space (for example a burrow). Note that female degus have a better sense of smell than males as it has been found that the hormone testosterone, present in males only, can de-sensitise a male degu's olfactory organs to certain scents⁷. Females also have four pairs of teats^{30, 52}, three pairs of which are located on the side of the body in a line between the front and hind legs⁵².

>DIGGERS?<
Degus are semifossorial² which means they are adapted for living partly (semi) underground (fossorial). This is in comparison with a fossorial mammal (for example a mole), which is almost completely adapted for life underground. Degu anatomy not consistent with burrowing includes large eyes, long toes, a long tail, smaller clavicle, smaller deltoid crest and nails instead of claws^{2, 52}.

>VITAL STATISTICS<
Degus are relatively similar in size and appearance between the sexes³⁰. Both have similar colouration and features, and both males and females weigh roughly the same² amount, depending on the time of year³⁷.  Interestingly, degus have the lowest body temperature of the caviomorphs⁴⁵.

Degus require 2% Isoflurane with 1.5 litres per minute of nitrous oxide and oxygen to provide surgical anaesthesia¹¹³.

>TEETH<
Degus, like their relatives the chinchillas, have orange enamel on their incisors with a multiserial microstructure^{52, 129}. This colouration occurs during amelogenesis⁵⁸, when the enamel is formed in ameloblasts (tooth enamel forming cells)⁵⁸. Amelogenins of developing dental enamel are specific proteins rich in proline, leucine, histidine and glutamyl residues that are synthesised by the ameloblast cells of the inner enamel epithelium⁵⁹. These proteins become mineralised to form mature enamel, thought to be regulated by an acidic enamel protein called tufletin⁵⁹. The exact process by which the enamel is coloured orange is still debated, but it has been suggested that the forming enamel is stained by oral enzymes in the degus saliva⁵⁷, although this is speculation only. It is hypothesised that such chromogenic enzymes are taken up by the pellicle⁶⁰ and are derived from polyphenolic compounds which provide the colour in foods⁶⁰. Therefore, it is thought nutrition plays a role in the enamel colour of degus teeth (see illness section). 

>OSTEOLOGY<
There is limited research on the of degus⁵². However, from reports, we know the following:
The has a large, well-developed infraorbital foramen⁵² with a ventromedial grove⁵² and an open pterygoid fossa⁵². The tip of the hamulus pterygoideus is in contact with the bulla⁵². The bulla are of moderate size⁵², but the auditory bulla is well developed⁵² and the paroccipital process hugs the posterior edge and surface⁵². Interestingly, the malleus and incus ossicles are not fused¹²⁹. In the mandible, the two rami are closely joined⁵², with the coronoid process appearing delicate and sharply pointed⁵². The clavicle and deltoid crest are well developed⁵². The scapular spine extends from near the vertebral border of the scapula to past the height of the tip of the coracoid process⁵². The scapular spine is a thin, unsupported, fingerlike projection from the midscapular region to the ends of the large acromion and metacromion processes⁵². There is an entepicondyloid foramen in the humerus⁵², and the proximal ends of the tibia and fibula are fused⁵². 

>MUSCULATURE<
There are several important myological characteristics that distinguish the degu. There is a complex, four parted M. cutaneus maximus in which the anterior part extends to the lateral surface of the shoulder⁵². There is a M. scapuloclavicularis⁵², a M. scalenus anterior ventral to the brachial plexus⁵² and the lack of a M. stylohyoideus despite having a well developed hyoid aparatus⁵². There is also a M. mandibulolabialis consisting of a complex multiparted group of masticatory muscles, with the medial masseter passing through the infraorbital foramen and pars reflexa of the superficial masseter, passing into the medial side of the mandible via a grove⁵². It is interesting to note that the musculature of the degu is consistent with all other hystricognaths, but is not found in any other rodent group⁵².

>EATING AND DIGESTION<
Degus are herbivorous¹² (eat plant matter only), so their digestive system is specifically adapted for this. Their gut contains sucrase³⁴, an enzyme that hydrolyses plant carbohydrates³⁴. This allows degus to digest sugars specific to plants, but due to abnormal insulin function, degus should avoid being fed diets containing sugar. Degus possess a caecum, which varies in form and position between degus¹³⁶. The Caput caeci is typically on the left with cranial or caudal rotation¹³⁶, the apex being on the left in front of the pelvis¹³⁶. The ascending colon is arranged in varying superimposed and often spiral folds¹³⁶.

Newborn pups also possess the enzyme lactase which enables them to digest their mother's milk³⁴.

Degu are small, dry, compact and very inoffensive. They don't smell and are very easy to clean up.

>VISION<
The degu lens selectively absorbs short-wavelength light¹³⁹, with increasing optical density as the degu gets older¹³⁹. Degu retinas possess one type of rod cell¹³⁹ and two types of S-cones^{24, 139} so can see in dichromatic colour²⁴. The colours visible to degus are green and UV (Ultra-Violet)^{24, 21, 139}. The rods have a spectral peak at 500 nm (green)¹³⁹, with each respective type of cone cell having spectral peaks at 507 nm (green) and 362 nm (UV)¹³⁹. The retinas consist of around 9 million photoreceptors¹³⁹, one-third of which are cone cells¹³⁹. The two cone types exist in a ratio of 13:1 (green:UV)¹³⁹.

To see an estimated example of what the world looks like to a degu, click here (note- humans can't see UV!).

Having UV sensitive S-cones is relatively uncommon in mammals²⁴. Degus have been shown to be able to distinguish between UV and visible light in behavioural tests¹³⁹.

>DAY-GLO DEGUS?!<
Degus fur is camouflaged, however their ventral (belly) fur is lighter⁵² and highly UV reflective and reflects up to 20% of UV light²¹ suggesting a signal for communication during alarm calls or vigilance, where degus expose their bellies by standing on their hind limbs²¹.

Degus urine also reflects UV and up to 40% of incident light²¹, acting as a visual territorial scent mark²¹.

>COLOUR VARIATION<
Did you know that degus come in more than one colour? Of course degus are normally brown^{51, 52} in colour, each hair being gray below and brown at the tip (also known as 'agouti'), but there are slight in pigmentation. Some degus are lighter than others⁵², whilst some can appear a very dark brown. Coat colour can also vary slightly depending on on season, age and diet. 

There are also new colour varieties under development around Europe. Details and pictures of these varieties can be found on the 'colour varieties' page.

>SEXING<
Although degus have different genital anatomy for males and females, it can be quite hard to tell them apart just by glancing. Their urogenital anatomy is similar to that of other caviomorphs⁴⁵. have a pair of testes that are always inside the abdomen^{45, 133}. The penis points posteriorly¹³³ from the perianal circle⁴⁵, beneath which (internally) is the cremasteric sac⁴⁵. The penis is stored internally in an S-shape¹³³ and the tip is covered with tiny spines¹³³. Inside the body, the vas deferens and seminal vesicles open independently into the urethra⁴⁵. The testicular artery is short, with few loops and a wide diameter⁴⁵. A sacculus urethralis is present¹²⁹.  have a bicornuate uterus⁵², which branches into two sections. The vaginal opening is located immediately (posteriorly) behind the urethral projection. Externally, females also have four pairs of nipples, three of which are positioned high on the sides between the front and hind limbs⁵². One pair is positioned on the belly between the hind limbs to enable suckling to occur whilst the female is vigilant.

, there is a larger distance between the anus and urethra in the male, whereas the female has virtually no space at all between the urethra and anus.

>SPERMATOZOA<
Degus' spermatozoa are different from other species. The head measures 7.7μm long by 5.9μm wide⁴⁷ while the tail is 41μm long⁴⁷. The head is flattened dorso-ventrally and oval in outline⁴⁷. The gametic DNA content is about 2.7pg⁴⁸. An interesting feature is that there is a recombination index of 73⁵², which is high for rodents⁵².

The acrosome is the most distinctive feature in the sperm of the degu⁴⁷. Viewed head-on, the rim of the acrosome is the shape of an inverted 'U'⁴⁷. The acrosomal region has dome-shaped protrusions that are regular (not random)⁴⁷. The acrosome makes up about 60% of the head length⁴⁸.

There are also subtle differences in the morphology of sperm between degu species. The sperm head of the Bridge's degu is more elyptical than rounded⁴⁸, whereas that of the moon tooth degu is paddle shaped and basally broader⁴⁸. On average, the common degu has the smallest sperm head length⁴⁸, Bridge's degu has the smallest sperm head width⁴⁸ and the moon tooth degu has the shortest sperm tail length⁴⁸.  

>PLACENTA AND OVARIES<
During pregnancy, the placenta has a hemomonochorial placental barrier with continuous, non-fenestrated capillaries¹¹². At day 27 of gestation the subplacenta emerges under the wall of the central excavation¹¹⁴ and the outermost trophoblast of the ectoplacental cone begins differentiation¹¹⁴. These secondary trophoblast giant cells lie on the outside of the placenta forming an interface with the maternal cells of the decidua¹¹⁴. These cells contain cytokeratin and placental lactogen until term¹¹⁴. During gestation the extrasubplacental trophoblast merges from the subplacenta to the decidua¹¹⁴. The vascular mesenchyme of the central excavation invades the chorioallantoic placenta during gestation to form two foetal lobules which is the zone of the placental barrier¹¹⁴. The activity of sodium and potassium ion ATPase in the placental barriers constant throughout gestation¹¹⁴. The residual syncytium at the edge of the placental disc/between the lobules is not invaded by foetal mesenchyme and forms the marginal and interlobular labyrinthine syncytium¹¹⁴. These cells are likely to have a secretory process between maternal blood vessels¹¹⁴. Placentas passed out of the body during birth show a large, single lobe, have no subplacenta and a reduced interlobular labyrinthine syncytium¹¹⁴. The inverted visceral yolk sac can be seen at day 27 of gestation and has features to suggest it functions as an early secretory organ¹¹⁴. The epithelium of the parietal yolk sac covers the entire placenta¹¹⁴, and comes directly into contact with the uterine lumen¹³⁵. The full-term placental weight is roughly 8 g and has a diameter of around 13 mm¹³⁵.

Even from an early age, females posses an antral follicle in the ovaries¹³⁴ which does not ovulate, but becomes atretic¹³⁴. Interstitial tissue is abundant¹³⁴, and interstitial cells are vacuolated and possibly involved with synthesis of steroids¹³⁴. During pregnancy, the corpus luteum persists throughout¹³⁴, but may regress towards parturition¹³⁴. Several small accessory luteal bodies are formed toward the end (days 75-80) of pregnancy¹³⁴, persisting up to 20 days after parturition¹³⁴. Other structures present in the ovaries include epoophoron tubules¹³⁴ and rete ovarii¹³⁴.