Branching patterns of the adrenal arteries in the degu (Octodon degus)

The degu has drawn increasing attention for use as an experimental animal in stress response studies due to its physiological features, such as diurnality and seasonal breeding, which differ from conventional laboratory rodents. Stress response is elicited by steroid hormones secreted by the adrenal gland, whose functions are controlled by pituitary hormones reaching through the adrenal arteries. However, knowledge of the arterial anatomy of the degu adrenal gland remains insufficient. To address this issue, we observed adrenal arteries in 20 male degus injected with red-colored latex. Adrenal arterial branching patterns were classified into Types 1-4, which respectively have 1 to 4 parent arteries that give rise to the adrenal arteries. Based on the combination of the parent arteries, Types 2 and 3 were categorized into subtypes a to c, while Type 4 was categorized into subtypes a and b. On the left side, Type 2 (45%) and Type 3 (45%) were predominant, whereas Type 1 (5%) and Type 4 (5%) were infrequent. On the right side, Type 2 (50%) and Type 3 (45%) were predominant, whereas Type 4 (5%) was infrequent. Type 1 was not present. There were 0 to 4 cranial, 1 to 4 middle and 1 to 4 caudal adrenal arteries, with the total number varying from 2 to 9. The present observation provides knowledge of comparative anatomical features of the degu adrenal arteries, which can serve as an anatomical basis for comparative endocrinological studies.

Influence of Pre-Weaning Social Isolation on Post-Weaning Emotion Tendency and Mother-Infant Interactions in Infant Octodon Degus

Our previous research using Octodon degus (degus) revealed that preweaning social isolation negatively affected object exploratory behavior. However, it remains unknown how social isolation affects animal psychology and other behaviors. The present study examined the effects of neonatal social isolation on degu emotion and mother–infant interactions before and after weaning. Because degus have a complex social repertoire, we predicted that they would be sensitive to social isolation and show similarities with humans in their social interaction. Pups in the isolation group were separated from their family seven times for 30 min a day from 8 to 15 days post-birth. Pups in the nonisolation group were reared with their family. At 2, 3, 4, 5, and 6 weeks of age, pups underwent a zero-maze test to measure anxiety and a mother–infant interaction test to assess mother–infant attachment. Isolated pups showed more activity in the zero-maze test than nonisolated pups at 3 weeks of age. We found no significant effects of social isolation on mother–infant interactions. These results suggest that while neonatal social isolation might affect emotion during weaning, it does not influence mother–infant relationships.

Stress, sleep, and sex: A review of endocrinological research in Octodon degus

The Common Degu (Octodon degus) is a small rodent endemic to central Chile. It has become an important model for comparative vertebrate endocrinology because of several uncommon life-history features - it is diurnal, shows a high degree of sociality, practices plural breeding with multiple females sharing natal burrows, practices communal parental care, and can easily be studied in the laboratory and the field. Many studies have exploited these features to make contributions to comparative endocrinology. This review summarizes contributions in four major areas. First are studies on degu stress responses, focusing on seasonal changes in glucocorticoid (GC) release, impacts of parental care on offspring GC responses, and fitness consequences of individual variations of GC responses. These studies have helped confirm the ecological relevance of stress responses. Second are studies exploring diurnal circadian rhythms of melatonin and sex steroids. These studies have formed important work translating circadian biology from nocturnal laboratory rodents to diurnal humans. Third are studies that exploit the open nature of degu natural habitat, combined with laboratory studies, to explore the impact of testosterone on agonistic behavior. Studies have focused primarily on male:male, female:female, male:female, and parental behaviors. Fourth, are contributions to the study of female masculinization from male siblings in the uterus. These studies have focused on both the behavioral consequences of masculinization and the impact of those behaviors on fitness. Taken together, the studies reviewed here have formed a strong foundation for further studies in the degu so that future studies can address how endocrinological components underlie new mechanistic connections to the ecological effects on behavior and fitness.

Seasonal variation in the degu (Octodon degus) endocrine stress response

Many wild animals show seasonal variation in circulating levels of stress hormones. Seasonal changes in the stress response may help animals better cope with the different challenges faced during each life history stage. We determined the seasonal stress profile of wild, free-living degus in Chile. Female degus were sampled during non-breeding (January), mating/early gestation (July), late gestation (August), and lactation (1st litter-September, 2nd litter-January). Male degus were sampled during the first three time-points. We measured baseline cortisol (CORT), stress-induced CORT, and negative feedback efficacy using a dexamethasone suppression test. While we found that neither males nor females showed seasonal variation in baseline CORT or negative feedback levels, we did find significant seasonal variation in stress-induced CORT levels of both sexes. Male stress-induced CORT was lowest during mating while female stress-induced CORT was highest during late gestation and lactation. Overall, females had higher stress-induced CORT compared to males. Our data suggest that stress-induced levels of CORT are highest during periods with increased chance of stressor exposure or times of positive energy balance. Consequently, CORT responses to stress appear to be regulated according to different life history needs.

Fecal cortisol levels predict breeding but not survival of females in the short-lived rodent, Octodon degus

The cort-adaptation hypothesis indicates that an association between glucocorticoid (cort) levels and fitness may vary with the extent to which reproduction or breeding effort is a major determinant of cort levels. Support for a context dependent association between cort and fitness comes mostly from relatively long-lived, bird species. We tested the hypothesis that there are gender and context (life-history) specific cort-fitness relationships in degus, a short-lived and generally semelparous social rodent. In particular, we used demographical records on a natural population to estimate adult survival through seasons and years and linked that to records of baseline cort (based on fecal cortisol metabolites). We found no evidence for a direct relationship between baseline cort and adult survival across seasons, and this lack of association was recorded irrespective of sex and life history stage. Yet, cort levels during early lactation predicted the probability that females produce a second litter during the same breeding season, supporting a connection between baseline cort levels and breeding effort. Overall, the differential effects of cort on survival and breeding supported that the extent of cort-fitness relationships depends on the fitness component examined.

Husbandry and breeding in the Octodon degu (Molina 1782)

The Octodon degu is a native rodent species from South America, which lives in colonies with a well-structured social organization grouping of 5-10 young and 2-5 adult animals sharing a burrow system. They show a temperature-dependent diurnal-crepuscular activity pattern. In nature they rarely survive 2 yr, mostly because of predation. However, in captivity, females reproduce for 4-4.5 yr, and both sexes live for 5-7 yr. Males remain fertile until death. Some care is required to maintain healthy degus, particularly breeding females. Here we describe husbandry and breeding guidelines from the experience of the University of Michigan degu colony. With the husbandry practices described here, 90% of pups born in our colony reach maturity (6 mo of age), and no diarrheal diseases are apparent in our adult population.