Octodon degus: a diurnal, social, and long-lived rodent

Octodon degus is a moderate-sized, precocious, but slowly maturing, hystricomorph rodent from central Chile. We have used this species to study a variety of questions about circadian rhythms in a diurnal mammal that readily adapts to most laboratory settings. In collaboration with others, we have found that a number of fundamental features of circadian function differ in this diurnal rodent compared with nocturnal rodents, specifically rats or hamsters. We have also discovered that many aspects of the circadian system are sexually dimorphic in this species. However, the sexual dimorphisms develop in the presence of pubertal hormones, and the sex differences do not appear until after gonadal puberty is complete. The developmental timing of the sex differences is much later than in the previously studied altricial, rapidly developing rat, mouse, or hamster. This developmental timing of circadian function is reminiscent of that reported for adolescent humans. In addition, we have developed a model that demonstrates how nonphotic stimuli, specifically conspecific odors, can interact with the circadian system to hasten recovery from a phase-shift of the light:dark cycle (jet lag). Interestingly, the production of the odor-based social signal and sensitivity to it are modulated by adult gonadal hormones. Data from degu circadian studies have led us to conclude that treatment of some circadian disorders in humans will likely need to be both age and gender specific. Degus will continue to be valuable research animals for resolving other questions regarding reproduction, diabetes, and cataract development.     

IMPLICATIONS FROM PHYSIOLOGICAL STUDIES OF MARINE MAMMALS1

Some aspects of captive marine mammal research have become matters of controversy, largely due to a misunderstanding of the value of such studies and of their importance to effective management and conservation of these species. Understanding of the physiological mechanisms underlying the special adaptations for aquatic life that marine mammals demonstrate provides essential information relating to their health and survival. The need for such information is increasing as disturbance of the world's marine environments steadily escalates. While studies of these animals in their natural habitats contribute much to our comprehension of their biology, a more complete understanding of the physiological basis of their behavior depends upon experimental laboratory investigations. Some of the new knowledge thus gained has potentially important implications for human medicine.     

THERMOREGULATORY ADAPTATIONS IN MARINE MAMMALS: INTERACTING EFFECTS OF EXERCISE AND BODY MASS. A REVIEW1

A review of thermoregulation in marine mammals led to the following conclusions: very little is known about thermoregulation in large cetaceans. The only measured value for the metabolic rate of a whale, albeit a young one, was substantially higher than the predicted value for a terrestrial mammal of similar size. Very small and newborn marine mammals rely on a high metabolic heat production to sustain their body temperature during exposure to cold or in the water. The considerable insulation of some adult marine mammals may absolve them from the need for a high level of heat production. One marine mammal in tropical or subtropical waters is hypometabolic. There is evidence for a powerful control of thermoregulatory mechanisms by the anterior hypothalamic/preoptic region of the brain in two species. Thermoregulation in marine mammals during exercise remains paradoxical.     

The active avoidance reaction of laboratory rats: differences between experiments carried out in the phase of motor activity and inactivity

The influence of two phases of the circadian cycle (motor activity and motor inactivity) on the rate of acquisition and extinction of an active avoidance reaction was studied in 35-day-old male laboratory rats reared in cages (with limited social contacts), in young reared from the age of 15 days in communities (with the broad social contacts typical of this species) and in adult males reared in cages. A difference was found between the results of experiments carried out in the morning (during the motor inactivity period) and in the early evening (at the outset of the motor activity period) in both young and adult animals. The factor deciding whether acquisition or extinction was influenced depended on the mode of life. In animals reared in cages, inhibition was influenced; extinction was elaborated faster in the evening in adult animals and juvenile young were capable of 100% extinction only in the evening (in the morning only 50%). Community young achieved 100% extinction in both cases. In young rats which lived in a community from the 15th day, acquisition was influenced (it was achieved faster in the evening). The correlation between the rate of acquisition and extinction in cage-bred adult and young rats was negative if the experiments were carried out in the morning and was positive in evening experiments on young animals. In community-bred young it was positive in both cases.     

Small mammal abundance in relation to microhabitat in a dry sub-humid grassland in Kenya

Six species of rodents and two species of insectivores, live-trapped on a 1 ha grid over a 27 month period, were studied in relation to microhabitat factors in a dry sub-humid grassland in Kenya. Wet season peaks of small mammal species were followed by low numbers trapped during the dry seasons. Species distributions were correlated with different microhabitat parameters, and the separation of species with apparently similar environmental requirements could be explained largely in terms of current knowledge of the biology of the species. Correlation analyses indicated an ecological separation of two closely-related Mus species and of two Crocidura shrews. Overlap indices were extremely high, ranging from 0.556 to 0.877 for all combinations of pairs of species. It seems likely that neither food nor micro-habitat partitioning completely explains the coexistence of the small mammal species and it is suggested that populations are highly transient, moving from refuge areas into temporarily favourable areas during the wet season.     

Features of the circadian rhythm of temperature of the skin at children of 8-9 years and young men and girls

Problem of the present work was studying age features circadian rhythm of temperature of a skin with application of a method "Termochron iButton". Day-night rhythm of a skin temperature at two age-grades was investigated: boys and girls of 8-9 years and young men and girls of 20-22 years. For this purpose monitoring temperature during 48 hours with an interval of registration 10 minutes has been lead. Are revealed authentic chronobiological differences: mesor temperatures above at girls, than at boys, and at young men, above, than at girls. Amplitude of a circadian rhythm is above at boys and at girls. Researches chronobiological parameters in the different terms of day have shown, that an average level of temperature at night below at all examinees. The amplitude at adult people in the different terms of day does not differ, while at children it above in the night term.     

Rhythms in a diurnal brain

The neural mechanisms governing circadian rhythms generate patterns of behavior and physiology that are very different in diurnal and nocturnal species. Here we review data bearing on the issue of where and how in the brain these differences might be generated. Molecular data from several species now confirm that the central circadian clock, located in the suprachiasmatic nucleus (SCN), is coupled to the light - dark cycle in the same manner in nocturnal and diurnal species, indicating that the fundamental differences arise from mechanisms coupling the clock to effector systems. Major differences in this coupling become apparent only when one steps beyond the SCN to look at brain regions that directly or indirectly receive input from it. This review focuses on our work on brain regions and cell populations to which the SCN projects in the diurnal species Arvicanthis niloticus (Nile grass rats). We have found rhythms in the numbers of cells containing cFos, or PER1, in a number of these regions, and the patterns of these rhythms are always different from those seen in nocturnal laboratory rats. In some areas these rhythms are simply inverted in the two species, but in other extra-SCN regions the phase of the rhythms in these two species differs in less extreme ways. Taken together, these data suggest that there is no single simple switch that causes some animals to be nocturnal and others to be diurnal. Rather, the differences likely emerge through a variety of mechanisms operating within and downstream of the cells to which the SCN projects.     

Seasonal and successional dietary shifts of two sympatric rodents in coastal heathland: A possible mechanism for coexistence

Abstract Using microscopic analysis of faecal pellets, we compared the seasonal and successional patterns of food resource use of two Australian native rodents, the eastern chestnut mouse (Pseudomys gracilicaudatus) and the swamp rat (Rattus lutreolus) in a coastal heathland at Myall Lakes National Park, New South Wales. Using the Mantel test, the diets of the two mammal species were significantly different in autumn and winter but not in spring and summer. Further, the two species showed differential use of resources at the young and middle-aged stages of vegetation succession following fire. The mean dietary overlaps for pairs of individuals between the two species were relatively high in all seasons and successional stages, but they were significantly lower than those for pairs of individuals within each species in autumn and winter, and at the young and middle successional stages. Analysis of dietary niche position (γ) and breadth (β) showed lower γ and larger β for P. gracilicaudatus than for R. lutreolus, confirming previous observations that R. lutreolus is more specialized, and less opportunistic in diet than P. gracilicaudatus. Overall, the dietary separations of the two species were less marked in canonical space than they were for specific seasons and successional stages. These results, together with previous studies, indirectly suggest that while these two mammal species may be partitioning diet in autumn and winter in the middle stages, for spring and summer in the old successional stage they might need to partition habitats to facilitate their coexistence. Our results indicate that the local community is more dynamic and complex than previously thought and that other mechanisms of coexistence (e.g. temporal rotation of food resources) may be operating rather than traditional habitat and diet separation.     

Phase response curve to 1 h light pulses for the European rabbit (Oryctolagus cuniculus)

While much is known about the circadian systems of rodents, chronobiological studies of other mammalian groups have been limited. One of the most extensively studied nonrodent species, both in the laboratory and in the wild, is the European rabbit. The aim of this study was to extend knowledge of the rabbit circadian system by examining its phasic response to light. Twelve Dutch-Himalayan cross rabbits of both sexes were allowed to free-run in constant darkness and then administered 1 h light pulses (1000 lux) at multiple predetermined circadian times. Changes in the phase of the rabbits’ circadian wheel-running rhythms were measured after each light pulse and used to construct a phase–response curve (PRC). The rabbits’ PRC and free-running period (τ) conformed to the empirical regularities reported for other predominantly nocturnal animals, including rodents and predatory marsupials. The results of the study are thus consistent with reports that the rabbit is essentially a nocturnal animal and show that it can entrain to light/dark (LD) cycles via discrete phase shifts. Knowledge about the rabbit’s circadian range of entrainment to LD cycles gained in this study will be useful for examining the putative circadian processes believed to underlie the unusual rhythm of very brief, once-daily nest visits by nursing rabbit mothers and other nursing lagomorphs.     

The role of the circadian system in fractal neurophysiological control

Many neurophysiological variables such as heart rate, motor activity, and neural activity are known to exhibit intrinsic fractal fluctuations – similar temporal fluctuation patterns at different time scales. These fractal patterns contain information about health, as many pathological conditions are accompanied by their alteration or absence. In physical systems, such fluctuations are characteristic of critical states on the border between randomness and order, frequently arising from nonlinear feedback interactions between mechanisms operating on multiple scales. Thus, the existence of fractal fluctuations in physiology challenges traditional conceptions of health and disease, suggesting that high levels of integrity and adaptability are marked by complex variability, not constancy, and are properties of a neurophysiological network, not individual components. Despite the subject's theoretical and clinical interest, the neurophysiological mechanisms underlying fractal regulation remain largely unknown. The recent discovery that the circadian pacemaker (suprachiasmatic nucleus) plays a crucial role in generating fractal patterns in motor activity and heart rate sheds an entirely new light on both fractal control networks and the function of this master circadian clock, and builds a bridge between the fields of circadian biology and fractal physiology. In this review, we sketch the emerging picture of the developing interdisciplinary field of fractal neurophysiology by examining the circadian system's role in fractal regulation.     

Garden dormouse (Eliomys quercinus, Linnaeus 1766) without fenestration in angular process

One of the skull traits that separates the Leithiinae subfamily from other subfamilies of Gliridae family is a prominent fenestration in the angular process of the mandible. There is no reference in the literature of dormice from Leithiinae subfamily without this fenestration. However, some garden dormice (Eliomys quercinus) have been found without this fenestration in Spain. This lack of perforation may be due to an ossification of the angular process related to bone growth. Garden dormice skulls from different parts of Spain kept in two mammal collections were revised in order to detect animals without fenestration and to take measures that differ between young and adult dormice. The measures recorded did not differ between dormice with and without fenestration, and so, the entire angular process is not the result of an ossification process. Thus, the discovery of specimens without fenestration in the angular process should be taken into account in studies which need the identification of this species and other species from Leithiinae subfamily based on skull and mandibles traits.     

Immunological development in nestling American kestrels Falco sparverius: post-hatching ontogeny of the antibody response

Avian research involving examination of immune function or testing of immunocompetence in wild birds has been based upon information on Galliforms, (chicken and quail) even though they are precocial, whereas most wild species with which ecologists, biologists and toxicologists work are altricial; blind, naked and completely dependent at hatching. Here we begin to address this gap in knowledge, offering insight into the early, post-hatching, humoral immune response in an altricial bird, the American kestrel (Falco sparverius). Over two breeding seasons, nestling kestrels were immunized with a non-pathogenic antigen, dinitrophenol keyhole limpet hemocyanin (DNP-KLH), between 3 and 9 days post-hatching and boostered 6 days later. Background levels, primary and secondary immune responses were measured using an enzyme linked immunosorbent assay. The specificity of our laboratory produced rabbit, anti-kestrel antibody was determined using a double immunodiffusion assay. Results showed the rabbit antiserum to have specific anti-kestrel IgG activity. Birds as young as three days old could successfully mount an antibody response, the magnitude of which increased with age at first vaccination. Early immunization did not compromise growth rate, nor did it affect the maximum secondary response. Comparatively, adult kestrels immunized during the same season and following the same protocol, had antibody levels four times higher than those of the nestlings.     

Cryopreservation of gametes and embryos of non-domestic species.

Many species of mammals are threatened or endangered. Methods of assisted reproduction that are being used with increasing frequency to produce offspring of domestic animals and humans are often viewed as offering innovative ways to reproduce non-domestic species as well. Uncounted millions of live young of domestic or laboratory species have been produced from gametes and embryos stored at -70 degrees C or below, sometimes for as long as 25 to 35 yrs. Such methods of cryopreservation are now being applied with increasing frequency and urgency to preserve gametes and embryos of non-domestic and threatened species to establish "genome resource banks" or "frozen zoos." But levels of success to produce live young from such cryopreserved gametes or embryos vary considerably from species to species, as well as from individual to individual. It is sometimes thought that differences among species in fundamental characteristics of their gametes may determine the efficacy of cryopreservation and the production of live young. However, it may not be that ineffective cryopreservation is responsible for low success rates. Rather, the limiting factor may be insufficient information and knowledge of the most basic reproductive biology of such non-domestic species. Even standard methods of cryopreservation may be completely adequate to act as a "temporary" expedient to preserve germplasm of non-domestic species to permit time to acquire a fuller understanding of the biology and behavior of non-domestic species.     

Molecular mechanisms of associative learning in mammal and mollusc

Recent work in this laboratory has begun to cast light on the biochemical mechanisms by which a cell stores associatively acquired information. This appears to occur principally via two general pathways. The first seems to be a long-term activation of protein kinase C (resulting in long-term alterations in protein phosphorylation) while the second involves changes in RNA synthesis. One striking aspect of these mechanisms in that they seem to be conserved across the species we have studied (rabbit and Hermissenda). In the present paper we review some of the studies that support the role of protein kinase C activation and RNA synthesis in memory formation.     

The colony environment, but not direct contact with conspecifics, influences the development of circadian rhythms in honey bees

Honey bee (Apis mellifera) workers emerge from the pupae with no circadian rhythms in behavior or brain clock gene expression but show strong rhythms later in life. This postembryonic development of circadian rhythms is reminiscent of that of infants of humans and other primates but contrasts with most insects, which typically emerge from the pupae with strong circadian rhythms. Very little is known about the internal and external factors regulating the ontogeny of circadian rhythms in bees or in other animals. We tested the hypothesis that the environment during early life influences the later expression of circadian rhythms in locomotor activity in young honey bees. We reared newly emerged bees in various social environments, transferred them to individual cages in constant laboratory conditions, and monitored their locomotor activity. We found that the percentage of rhythmic individuals among bees that experienced the colony environment for their first 48 h of adult life was similar to that of older sister foragers, but their rhythms were weaker. Sister bees isolated individually in the laboratory for the same period were significantly less likely to show circadian rhythms in locomotor activity. Bees experiencing the colony environment for only 24 h, or staying for 48 h with 30 same-age sister bees in the laboratory, were similar to bees individually isolated in the laboratory. By contrast, bees that were caged individually or in groups in single- or double-mesh enclosures inside a field colony were as likely to exhibit circadian rhythms as their sisters that were freely moving in the same colony. These findings suggest that the development of the circadian system in young adult honey bees is faster in the colony than in isolation. Direct contact with the queen, workers, or the brood, contact pheromones, and trophallaxis, which are all important means of communication in honey bees, cannot account for the influence of the colony environment, since they were all withheld from the bees in the double-mesh enclosures. Our results suggest that volatile pheromones, the colony microenvironment, or both influence the ontogeny of circadian rhythms in honey bees.     

The influence of environment,sex, and innate timing mechanisms on body temperature patterns of free-ranging black-tailed prairie dogs (Cynomys ludovicianus)

Mechanisms that influence body temperature patterns in black-tailed prairie dogs are not well understood. Previous research on both free-ranging and laboratory populations of black-tailed prairie dogs (Cynomys ludovicianus) has suggested that reductions in ambient temperature and food and water deprivation are the primary factors that stimulate torpor in this species. In other species, however, torpor has been shown to be influenced by a multitude of factors, including innate circadian and circannual timing mechanisms, energy status, and reproductive behaviors. Our objective was to clarify the influence of weather, sex, and intrinsic timing mechanisms on the body temperature patterns of free-ranging black-tailed prairie dogs. We monitored body temperatures of eight adult (>1 yr) prairie dogs from November 1999 to June 2000. Prairie dogs showed distinct daily and seasonal body temperature patterns, which reflected changes in ambient temperatures that occurred during these periods. These patterns of daily and seasonal heterothermy suggest that body temperature patterns of black-tailed prairie dogs may be driven by an innate timing mechanism. All prairie dogs entered torpor intermittently throughout winter and spring. Torpor bouts appeared to be influenced by precipitation and reductions in ambient temperature. Our results also suggest that reproductive behaviors and circadian timing may influence torpor in this species.     

Performance of individual species as indicators for large mammal species richness in Northern Tanzania

In order to prioritize areas for biodiversity conservation, conservation practitioners frequently employ a single species whose distribution is statistically related to overall species richness. However, the performance of single mammal species in terms of (1) their strength, (2) spatial and (3) temporal variability for predicting large mammal species richness has rarely been assessed. Drawing upon data from multiple vehicle-based surveys in four study sites with varying conservation management approaches in the Tarangire–Manyara ecosystem, we assessed the performance of thirteen candidate indicator species. Overall, we found that the association strength between the distribution of single large mammal species and overall large mammal species richness varied (1) considerably across four management units within the same ecosystem, (2) between seasons and (3) years. In contrast to a study carried out in central Tanzania, elephants performed poorly as an indicator of large mammal species richness. Applying our findings to conservation planning, we suggest that information on zebra and wildebeest distribution should be used for delineating corridors for large mammals between protected areas in this ecosystem. The distribution of these two species had a high correlation with overall large mammal species richness, and these correlations were relatively constant throughout time and space. More generally, our study suggests that the performance of indicator species (1) should be assessed across multiple seasons because snapshot surveys may provide biased estimates of indicator performance, (2), cannot necessarily be extrapolated to other ecosystems and (3) should be supplemented by ecological or functional considerations.     

Poor historical data drive conservation complacency: The case of mammal decline in south‐eastern Australian forests

Forested ecosystems of south‐eastern Australia now differ physically, compositionally and functionally from their condition prior to European settlement. Understanding these changes, and how native species and entire ecosystems have responded, is crucial for biodiversity conservation and ecosystem management. Here I argue that a combination of limited historical information and a knowledge base biased towards modern ecological studies has resulted in a distorted perception of ecosystem condition, hindering the instigation of effective biodiversity conservation measures. This argument is based on recently obtained information about changes to the non‐volant mammal community, which reveals relatively recent but underreported ecological changes, including major declines in species distribution and abundance, shifts in niche utilization and associated disruption of ecosystem functions. Ultimately, many mammal species are being denied the capacity to function to the extent they did historically. Following this re‐assessment, it is evident that current forest management does not adequately address contemporary conservation dilemmas posed by detrimental ecosystem changes. This is especially salient when most of the factors responsible for causing changes to the mammal community are still active and include forest management and utilization activities. Therefore, additional conservation measures are essential to meet forest stewardship and biodiversity conservation obligations. For the health, functionality and sustainability of forested ecosystems, native mammal species must be capable of functioning to their ecological potential and occupy their original niche. This will be facilitated by the suppression of threatening processes (primarily exotic species), ensuring ecologically sensitive fire regimes and the reintroduction/translocation of missing species. The recovery or restoration of forest functionality based on mammal conservation should have wide‐scale benefits for biodiversity conservation.     

Socially synchronized circadian oscillators

Daily rhythms of physiology and behaviour are governed by an endogenous timekeeping mechanism (a circadian ‘clock’). The alternation of environmental light and darkness synchronizes (entrains) these rhythms to the natural day–night cycle, and underlying mechanisms have been investigated using singly housed animals in the laboratory. But, most species ordinarily would not live out their lives in such seclusion; in their natural habitats, they interact with other individuals, and some live in colonies with highly developed social structures requiring temporal synchronization. Social cues may thus be critical to the adaptive function of the circadian system, but elucidating their role and the responsible mechanisms has proven elusive. Here, we highlight three model systems that are now being applied to understanding the biology of socially synchronized circadian oscillators: the fruitfly, with its powerful array of molecular genetic tools; the honeybee, with its complex natural society and clear division of labour; and, at a different level of biological organization, the rodent suprachiasmatic nucleus, site of the brain''s circadian clock, with its network of mutually coupled single-cell oscillators. Analyses at the ‘group’ level of circadian organization will likely generate a more complex, but ultimately more comprehensive, view of clocks and rhythms and their contribution to fitness in nature.     

The rabbit (<Emphasis Type="Italic">Oryctolagus cuniculus</Emphasis>) as a seed disperser in a coastal dune system

The aim of this study was to establish whether rabbit endozoochory affects plant community structure and whether it contributes to the dispersal of new species to areas open to colonisation. Fresh pellets were collected throughout the study area and from the youngest sandbars. The series of bars represents a gradient in terms of their age and Retama monosperma cover. At least 14 different species germinated from rabbit pellets and seed dispersal were observed throughout the year. Our results indicate that endozoochory is very important in dune ecosystems as it allows for the dispersal and colonisation of plants species with no evident dispersal mechanisms and those with several dispersal mechanisms.