Degus in Research

Degus have been used in all kinds of research for many years, but are becoming more popular as research subjects11 , 30 as they are unique animal models68. Degutopia looks to all this research to provide you with the most accurate, up-to-date information. Papers that Degutopia has used can be found stored in the Degu Information Group.

>DIABETES and CATARACTS<

Degus originally became popular as research animals due to the fact they can develop diabetes mellitus easily and rapidly1 , 34. Degus are a member of the Hystricognath order which have been shown to have a highly divergent insulin structure24b (insulin is a hormone that regulates blood sugar levels). Degus are therefore prone to diabetes as blood glucose regulation is only 1-10 % active compared to other mammals24b, although this hot topic is still highly debated and often receives conflicting reports.

As a consequence of sugar intolerance, degus are also prone to cataracts which therefore gives a large area for study34. This corresponds to the fact that degus have a higher level of aldose reductase in their retinas, compared to gerbils and rats36.

Further information on diabetes and cataracts in the degu can be found on the health page.

>BEHAVIOUR<

Degus are used in many behavioural experiments as they exhibit multiple behaviour chronotypes10 (show a complex variety of behaviours). Degus demonstrate some behaviours which appear to be unique (or certainly the first recorded incidence) among rodents, such as their ability to spontaneously stack objects in order of decreasing size85. Researchers in Japan have even found that degus can learn to use tools, for example the tiny rake shown below, to retrieve an out-of-reach reward (in this case a sunflower seed)173. This is the first time tool use has been seen in species other than apes and birds173. Now is that clever or what?

The degu manipulates a tiny rake to retreive a reward
^Figure 1- Researchers found the degus could retreive an out-of-reach seed by manipulating a tiny rake. Source: Okanoya, K., Tokimoto, N., Kumazawa, N., Hihara, S. and Iriki, A. (2008) 'Tool-use training in a species of rodent: The emergence of an optimal motor strategy and functional understanding", PLoS One, 3: e1860, doi:10.1371/journal.pone.0001860 (Ref: 173).

It has been known for researchers to distinguish between degus by marking them with 'correcting fluid'2 (more commonly known as Tipex)!! This is HIGHLY advised against as Tipex is TOXIC, and a more usual way for researchers to mark individuals is using small amounts of hair dye. Other researchers have been known to fit wild degus with coloured plastic collars to identify them107, or ear tags140.

The reason showing complex behaviour patterns is so useful is because some degu behaviour (and physiological characteristics) can be directly related to humans18 , 31.

Gender differences have been found for degus in learning and memory tasks- female degus were significantly slower than males to initially find their way out of a Barnes maze, but males became slower in subsequent repetitions180. Females also made significantly less memory errors than males and adopted a spatial strategy to work out the maze, while males preferred a more random approach180! The research suggested that acquiring new memories of learned tasks and storing them may be influenced differently by gender in degus180.

>CIRCADIAN RHYTHMS<

Degus are also frequently used in studies of circadian rhythms34, or how they reset their 'biological clocks' (i.e. tell what time of day it is). Circadian rhythms are regular oscillations in the value of behavioural and physiological variables of organisms that recur on a daily basis62. The fact that degus can show both diurnal (daytime) and nocturnal (nighttime) rhythms allows a unique opportunity for study10. Degus can also take non-photic cues to delay their circadian 'pacemaker' (e.g. relating to body temperature and running wheel access152, melatonin levels159, 151, and also to random nocturnal feeding times181). Further circadian study can be obtained prior to puberty, as degus have a delayed sexual development68, during which gonadal hormones modulate the circadian system144.

Of particular interest in this area is the fact that female degus (and, to a lesser extent, males145 , 153) are able to 'reset' their circadian rhythms by taking odour cues from other degus141 , 153. This is known to be species-specific and is probably linked to their social nature141. Circadian reentrainment after a phase shift has been found to be facilitated by female sex hormones141 , 145 but suppressed by testosterone in males145, meaning males can take longer to adjust their rhythms based on an odour cue from only one or two correctly entrained individuals. These differences are not seen in juvenile degus145, due to sexual immaturity.

Circadian rhythm variation is also used for research into sleep patterns, for which the degu is a particularly suitable subject68. This is most useful in the study of sleep-wake timing68. It has been demonstrated that after a period of sleep deprivation, degus have circadian systems that interrupt 'recovery sleep' in order to maintain a crepuscular pattern150.

>REPRODUCTION<

Degus are valuable in reproductive studies34.

Degu pups are popular for use in early post-natal studies as their degree of development at birth makes them ideal research candidates15. The maturity of of a newborn degu's sensory system allows them to respond to familiar and new environmental stimuli from birth18.

They are also very popular in mother-infant attachment research18 as pups form strong emotional bonds with both parents, in particular the mother.

>DEVELOPMENT<

Degus mature slowly34, taking time to develop their characteristics and physiological morphology, compared with other species such as mice, rats and hamsters34. This allows a unique opportunity for developmental study. Separation stress is commonly studied in degu pups and it has been shown that pups repeatedly separated from their mother/litter during development exhibit behavioural abnormalities in adulthood similar to Attention Deficit Hyperactivity Disorder (ADHD) in humans161. This is treated with the drug methylphenidate, which also reverses some of the developmental abnormalities in degus161.

>AGEING<

Degus have a high degree of genetic heterogeneity39, making them a good model to study ageing in wild animals39.

It was recently discovered that degus possess remarkably similar neural Alzheimer's markers to those in humans142, which until now were presumed to be absent in rodent brains. This makes the degu the first rodent species to display neurodegenerative processes associated with Alzheimer's disease142. It has also been found that the onset of the disease typically occurs in captive-bred degus over 6 years old174, and that the onset of the disease may be delayed in captive-bred degus as compared to wild degus174.

>PAIN<

Research has shown that degus are more resistant to pain than rats (P<0.001)41. Degus also show a higher tolerance to the analgesic effect of morphine compared to rats (P<0.01)41. This has interesting implications for research.

>WILD DEGU RESEARCH<

Researchers have studied the effect of climate and climate change on wild degu population levels. Although Chile has a semi-arid climate, the country is affected periodically by El Niño (exceptionally high rainfall) and La Niña (exceptionally low rainfall) climate events. Degu populations were found to do better than average during multiple El Niño years, due to the higher abundance of food/resources175. Because global climate change is likely to lead to an increase in the frequency of El Niño years, this could mean degu numbers will increase in the future175.

Interestingly, when wild degus need to be caught in order to weigh them, etc, before release, it has been shown that the males do not show a rise in testosterone or cortisol (stress) levels when kept up to 2 hours inside special traps107. Whether females show a similar tolerance is not known.

Another important area of wild degu research is their ability to carry zoonotic infections (those that can be passed between species). Wild degus are an intermediate host (i.e. they carry but are not affected by) of the parasite Trypanosoma cruzi. This parasite causes 'Chagas disease' in its target host, such as humans. A recent study has found that degus could be acting as a 'reservoir' for the parasite, as up to 70 % of wild degus tested showed positive for infection with the parasite189. I should point out that captive degus outside south America do not have this infection, so there's no need to worry!

>LOCOMOTION<

Degus have been used as a representative model to study the trot-gallop transition in small mammals146. The rate of metabolism and transport cost has been found to increase by 30 % per 20 % increase in body mass146. Interestingly, this is higher than that demonstrated in other mammals, although similar to that of humans146. The transition itself was found not to conform with either the hypothesis that gate changes due to energy consumption, or the hypothesis that gate changes due to musculoskeletal stress146.