Octodon degus (Molina 1782): A Model in Comparative Biology and Biomedicine (original) (raw)
Related papers
2003
To determine the eye's spectral sensitivity in three species of the genus Octodon (order Rodentia; infraorder Caviomorpha), O. degus, O. bridgesi, and O. lunatus, as well as the spectral properties of the animals' fur and urine and of objects in their habitat. The genus is endemic in Chile and contains species with different habitats and circadian patterns (diurnal versus nocturnal). METHODS. The electroretinogram (ERG) was used to record scotopic and photopic spectral sensitivity. The reflectance of ventral and dorsal body parts, urine, and other objects from the natural microhabitat were measured with a fiber-optic spectrometer. RESULTS. In scotopic conditions, the maxima of sensitivity ( max ) were at 505.7 Ϯ 7.7 nm in O. degus, 501 Ϯ 7.4 nm in O. bridgesi, and 510.1 Ϯ 7.4 nm in O. lunatus, representing the rod mechanism. In photopic conditions, only the diurnal species O. degus (common degu) was studied. The degu's photopic sensitivity had a max at 500.6 Ϯ 1.2 nm and contained two cone mechanisms with max at 500 nm (green, medium-wavelength-sensitive [M] cones) and approximately 360 nm (ultraviolet, short-wavelength-sensitive [S] cones). In all three Octodon species, dorsal body parts were more cryptically colored than ventral ones, and ventral body parts had a significant UV reflectance. The fresh urine of O. degus, used for scent marking in various behavioral patterns, was also high in UV reflectance. CONCLUSIONS. It is suggested that territorial urine marks are visual as well as pheromone cues for UV-sensitive species and hence may have favored the evolution of UV-cones in rodents.
Chronobiology International, 2010
There are two main processes involved in the expression of circadian rhythmicity: entrainment and masking. Whereas the first operates via the central pacemaker to anticipate predictable environmental conditions, masking (mainly induced by light) functions as a direct modulator of the circadian output signal induced by nonpredictable events. The Chilean rodent Octodon degus presents both diurnal and nocturnal chronotypes when given free access to an exercise wheel. Two steady-entrainment phases and graded masking by light seem to generate the wide variability of chronotypes in this species. The aim of this study was to characterize the differential masking by light according to the individual chronotypes, their stability over time, and the influence of wheel running availability and ambient temperature upon the degus' nocturnality. To this end, diurnal and nocturnal degus were subjected to ultradian cycles (1:1-h light-dark [LD]), with and without wheel running availability, and under both normal and high diurnal ambient temperature cycles. The present results show that diurnal and nocturnal degus present a stable masking by light, each according to its respective chronotype. Thus, whereas diurnal animals increased their activity with light, in nocturnal degus light induced a sharp drop in wheel running activity. These two types of masking responses appeared not only when the animals were synchronized to the 12:12-h LD cycle, but also under ultradian cycles. Different masking effects persisted when wheel running was made unavailable and when the animals shifted their circadian activity patterns in response to ultradian cycles or to diurnal exposure to high temperatures. In conclusion, our results show that the positive and negative masking effects of light on diurnal and nocturnal degus, respectively, seem to occur independently of relative phase control by the central pacemaker or the negative masking induced by high environmental temperatures.
Does Nocturnality Drive Binocular Vision? Octodontine Rodents as a Case Study
PLoS ONE, 2013
Binocular vision is a visual property that allows fine discrimination of in-depth distance (stereopsis), as well as enhanced light and contrast sensitivity. In mammals enhanced binocular vision is structurally associated with a large degree of frontal binocular overlap, the presence of a corresponding retinal specialization containing a fovea or an area centralis, and welldeveloped ipsilateral retinal projections to the lateral thalamus (GLd). We compared these visual traits in two visually active species of the genus Octodon that exhibit contrasting visual habits: the diurnal Octodon degus, and the nocturnal Octodon lunatus. The O. lunatus visual field has a prominent 100u frontal binocular overlap, much larger than the 50u of overlap found in O. degus. Cells in the retinal ganglion cell layer were 40% fewer in O. lunatus (180,000) than in O. degus (300,000). O. lunatus has a poorly developed visual streak, but a well developed area centralis, located centrally near the optic disk (peak density of 4,352 cells/mm 2 ). O. degus has a highly developed visual streak, and an area centralis located more temporally (peak density of 6,384 cells/mm 2 ). The volumes of the contralateral GLd and superior colliculus (SC) are 15% larger in O. degus compared to O. lunatus. However, the ipsilateral projections to GLd and SC are 500% larger in O. lunatus than in O. degus. Other retinorecipient structures related to ocular movements and circadian activity showed no statistical differences between species. Our findings strongly suggest that nocturnal visual behavior leads to an enhancement of the structures associated with binocular vision, at least in the case of these rodents. Expansion of the binocular visual field in nocturnal species may have a beneficial effect in light and contrast sensitivity, but not necessarily in stereopsis. We discuss whether these conclusions can be extended to other mammalian and non-mammalian amniotes.
A nonphotic stimulus inverts the diurnal-nocturnal phase preference in Octodon degus
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1999
Mechanisms differentiating diurnal from nocturnal species are thought to be innate components of the circadian timekeeping system and may be located downstream from the circadian pacemaker within the suprachiasmatic nucleus (SCN) of the hypothalamus. In the present study, we found that the dominant phase of behavioral activity and body temperature (Tb) is susceptible to modification by a specific modality of behavioral activity (wheel-running activity) in Octodon degus, a mammal that exhibits multiple chronotypes. Seven Octodon degus exhibited diurnal Tb and locomotor activity (LMA) circadian rhythms while entrained to a 24 h light/dark cycle (LD 12:12). When the diurnal animals were provided unrestricted access to a running wheel, the overt daily rhythms in these animals inverted to nocturnal. This nocturnal pattern was sustained in constant darkness and returned to diurnal after removal of the running wheel. Six additional animals exhibited nocturnal chronotypes in LD 12:12 regard...
Seasonal Changes In the Time Budget of Degus, Octodon Degus
Behaviour, 2005
The activity budget of an individual is the allocation of time to all its activities, and is expected to vary in response to both internal and environmental factors that influence its energy acquisition, breeding success, and survival. We recorded seasonal variation in individual and social behaviour of a natural population of degus (Octodon degus), a diurnal, semi-subterranean and social rodent from central Chile. We related changes in degu activity to differences in sex, seasonality (breeding activity, abundance of high quality food), and abundance of degu predators. On average, degus allocated most of their time while active above ground to foraging (46%) and alertness (32%); activities such as resting (8%), locomotor activity (7%), self-grooming (3%), burrow digging (0.2%), dust-bathing (1%), and social interactions (3%) occupied a relatively small percentage of degus' time budget. Time spent in foraging and total vigilance did not vary seasonally, but they were inversely related, reflecting a trade-off. Degus adjusted bipedal vigilance and locomotor activity partially to the presence of predators. Sex interacted with seasonality to influence degu behaviour. Male degus dust-bathed more and were more aggressive toward conspecifics than females during breeding time. We hypothesize that breeding activity is a more important predictor than abundance of high quality food to account for these interactions.
Current Biology, 2002
eral organs of the body are synchronized to generate a concerted rhythm for the whole organism [11]. Among the genes driving the clock in the SCN are the two Period genes Per1 and Per2 [12-14]. Both homologs show a circadian rhythm of activation within the SCN and can serve as markers for the phase of the circadian clock [15-17]. Switzerland 2 Institute of Evolution Recent data indicate that, at both the behavioral and the molecular levels, the blind mole rat Spalax ehren-University of Haifa Mount Carmel bergi superspecies has a functional circadian clock despite its isolated subterranean ecotope [3, 6, 7]. Haifa 31905 Israel Twenty-five million years of selective adaptation to this environment have resulted in a radical degeneration of its visual system, leading to atrophied (600 m wide), totally fur-covered eyes that lack any image-forming Summary ability [18]. Interestingly, the degenerated retina contains opsins and melanopsin, which might be responsi-The subterranean mole rat Spalax ehrenbergi superspecies represents an extreme example of adaptive ble for light detection [19, 20]. The SCN, however, is well developed and receives clock-related signals from visual and neuronal reorganization [1, 2]. Despite its total visual blindness, its daily activity rhythm is en-the retina via the retinohypothalamic tract [7, 18, 21].
The Response of PER1 to Light in the Suprachiasmatic Nucleus of the Diurnal Degu ( Octodon Degus )
Chronobiology International, 2009
Several studies suggest that the circadian systems of diurnal mammals respond differently to daytime light than those of nocturnal mammals. We hypothesized that the photosensitive "clock" gene Per1 would respond to light exposure during subjective day in the suprachiasmatic nucleus of the diurnal rodent, Octodon degus. Tissue was collected 1.5 -2 h after a 30 min light pulse presented at five timepoints across the 24 h day and compared to controls maintained under conditions of constant darkness. Per1 mRNA was quantified using in situ hybridization. Results showed that the rhythmicity and photic responsiveness of Per1 in the degu resembles that of nocturnal animals. (
El Octodon degus es un roedor endémico de Chile que ha sido caracterizado como diurno tanto en su medio natural como en condiciones de laboratorio. Sin embargo, se ha descrito que algunos individuos invierten su actividad a nocturna cuando se les permite hacer ejercicio en una rueda giratoria instalada en su jaula. Esta tesis doctoral tiene como objetivos: entender este proceso de nocturnalismo, caracterizar los mecanismos circadianos implicados y definir el papel que juega el marcapasos central circadiano. Los resultados apuntan a que el nocturnalismo en los degus se basa en una respuesta termorreguladora de evitación temporal frente a altas temperaturas diurnas. Esta actividad nocturna la consiguen mediante encarrilamiento estable del reloj circadiano pero también mediante la inhibición de la actividad locomotora ante la presencia de luz (masking). Además, la secreción endógena de melatonina, o su administración exógena, como el propio marcapasos circadiano no parecen estar implic...
Biological Rhythm Research, 2010
The volcano mouse, Neotomodon alstoni, was studied in order to describe basic circadian behavior during free running and entrainment to parametric and nonparametric photoperiods. Responses to short and long days were also tested to ascertain any potential photoperiodic response. This species is endemic to the high grasslands of central Mexico. Its breeding peaks during summer, indicating a possible circannual regulation of reproduction. Our results indicate that locomotor activity in Neotomodon alstoni is typical of a nocturnal rodent when studied using running wheels, however, when activity was observed in freely moving recordings with no running wheel, locomotor activity shifts to a semidiurnal architecture when exposed to long day photoperiods. When gonadal activity was studied in males exposed to short and long days, significant differences were observed in testis size, nevertheless levels of testosterone and seminiferous tubuli indicated that day length does not inhibit sexual maturity in this species. The results indicated that N. alstoni may not be photoperiodic with regard to gonadal activity, however it does display photoperiodic differences with regard to behavior, body weight and testis size.