C. Jackson and RTF Bernard

Department of Zoology & Entomology, Rhodes University, Grahamstown 6140.
E-mail: r.bernard@ru.ac.za; or g94j2708@campus.ru.ac.za

The four striped field mouse occurs widely throughout southern Africa where it occupies a wide variety of habitat types. Reproduction is seasonal with inhibition in winter, although there are a few records of reproduction in winter (David & Jarvis, 1985). Spermatogenesis is not inhibited by short day length alone (Jackson & Bernard, 1999) and in this study we test the hypothesis that reproduction of males and females will be inhibited by an energetic challenge resulting from a reduction in food quantity and, or a reduced ambient temperature.
Reproductively active male and female four striped field mice (n >8 per treatment) were exposed to either 26°C or 15°C, and either ad lib. food, or a 10% reduction in their daily food intake for at least four weeks after which animals were sacrificed and all reproductive organs examined histologically. In male R. pumilio, both reduced ambient temperature and a reduction in food quantity had an inhibitory effect on spermatogenesis and size of the reproductive organs, and this was greatest when the two factors were combined and the effect of fat removed. Female R. pumilio responded differently and reproduction was inhibited by a reduction in food quantity irrespective of ambient temperature. We conclude that reproduction in R. pumilio from the Eastern Cape Province of South Africa is truly opportunistic, that reproduction will be inhibited by an energetic challenge, and that there is sexual dimorphism in the response to ambient temperature and food. Our current research is aimed at establishing the endocrine control of reproduction in the four striped field mouse and preliminary results for GnRH and leptin are presented elsewhere.

References
David JHM & Jarvis JUM (1985) Population fluctuations, reproduction and survival in the striped fieldmouse Rhabdomys pumilio on the Cape Flats, South Africa. Journal of Zoology London 207 251-276
Jackson C & Bernard RTF (1999) Short day length alone does not inhibit spermatogenesis in the seasonally breeding four-striped field mouse (Rhabdomys pumilio) Biology of Reproduction 60 1320-1323

Non-shivering thermogenesis in the Tasmanian bettong (Bettongia gaimardi) and the role of uncoupling proteins (UCP1, 2 and 3).

RW Rose¹, A Kabat¹ and A West²

¹School of Zoology and ²Discipline of Biochemistry, University of Tasmania, Hobart, Tasmania 7001

The Tasmanian bettong (Bettongia gaimardi) is a small marsupial able to increase its metabolic rate by non-shivering thermogenesis. Oxygen consumption increases in response to various stimuli: vasopressin, non-epinephrine, both a1 and b adrenergic stimulation thyroid hormone and cold-acclimation (CA)(4-5°C for 14 days). Moreover, the metabolic rate response to nor-epinephrine is enhanced after CA (71% increase ‘v’ 47% prior to CA). The ability to respond to these stimuli only appears after week 10 of the 15-week pouch life. We have attempted to locate the source and cause of the metabolic response. Brown adipose tissue (BAT) is totally absent in this species as in most marsupials. In addition, we have failed to locate the uncoupling protein (UCP1) associated with BAT. Our research led us to investigate skeletal muscle as a source of heat production in this species and we have located both UCP2 and UCP 3 in this tissue in cold-acclimated bettongs.

How Different are Juvenile Kangaroos in their Physiology: Implications for population dynamics.

Adam J. Munn and Terence J. Dawson

School of Biological Sciences, University of New South Wales, Sydney Australia, 2052.
(a.munn@unsw.edu.au, t.dawson@unsw.edu.au" t.dawson@unsw.edu.au)

The population dynamics of red kangaroos (Macropus rufus) in the Australian arid zone is tightly linked with environmental factors, which, in part, operate via the survival of juvenile animals. A crucial stage is that of the young-at-foot (YAF) kangaroos which have permanently left their mothers' pouch. We have examined the thermal biology and basic physiology of YAF red kangaroos to determine just how different juveniles are compared with adult red kangaroos. Over a wide range of environmental temperatures (-5°C to 45°C), YAF red kangaroos had a mass-specific metabolism that was generally twice that of adults, and total energy requirements 60 -70% of those of adults, despite the YAF's being three times smaller. Over the same range in ambient temperature (Ta), YAF kangaroos had total evaporative water losses (TEWL) that were not significantly different from those of adults. At thermoneutral Ta (Ta 25°C), TEWL from the YAF was 3.87 ± 0.40 Watts, compared with 7.97 ± 1.04 Watts for adults. At Ta 45°C, YAF and adult TEWL increased to 52.53 ± 4.67 Watts and 56.57 ± 4.56 Watts, respectively. By the time of final weaning young kangaroos showed little change in their resting energy and water requirements (at Ta 25°C), but did show reduced costs in terms of energy and water use at extremes of ambient temperature (-5°C and 45°C respectively). Preliminary data also suggest that YAF kangaroos have maintenance energy and nitrogen requirements considerably higher than those of adults. In their arid environment, young red kangaroos may need to remain close to water points, which would in turn restrict their ability to find the high quality forage needed to meet their high resource requirements.

Prolonged Longevity in Naked Mole-rats: Physiological Changes

T.P. O’Connor, B. Andziak, A. Lee, J.U.M. Jarvis and R. Buffenstein

City College of the City University of New York and the University of Cape Town.
(Rochelle@harold.sci.ccny.cuny.edu)

Aging is a ubiquitous process characterized by a progressive decline in physiological processes with a concomitant decline in metabolism. Deleterious effects of aging are attributed to accumulated oxidative damage to cellular membranes, and DNA by reactive oxygen species (ROS). The induced damage is a by-product of oxygen consumption, and thus lifetime energy expenditure (LEE) is an index of exposure to ROS. If the oxidative damage theory of aging is valid, then long-lived species must a)have low values of lifetime oxygen consumption, b)generate fewer ROS, or c)have greater antioxidant defenses than shorter-lived species. Our ultimate goal is to test this in the longest-lived rodent known, Heterocephalus glaber. Maximum lifespan of naked mole-rats in captivity exceeds 25 years. Both this and the average lifespan (>10y) are considerably greater (>7 times) than those of mice. This study aims to: 1) establish a reliable index of LEE by measuring resting and peak metabolism at varying ages (1-20y), 2) determine the relationship between metabolism and body composition (using dual x-ray absorptiometry-DEXA), and 3) characterize antioxidant defenses of naked mole-rats.
Neither resting nor peak metabolic rate declined significantly with age. Nor were age-related changes in bone mineral density (BMD), %body fat, or %lean mass evident. These results differed from the typical mammalian pattern of declining metabolism, %lean mass, and BMD. Our estimate for lifetime energy expenditure, 1100 kcal/g, is the highest value known for rodents and amongst the highest for all mammals. Hence this species represents a valuable model for studying the oxidative damage theory of aging.

Evolutionary physiology and human exercise physiology: finding common ground.

Sue Jackson

Department of Human and Animal Physiology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
( sjack@land.sun.ac.za)

The historical divide between human and animal physiology is narrowing, particularly in fields such as hypoxic physiology where recent inter-population comparisons of hypoxic reponses are incorporating the “comparative approach” into classical human exercise physiology. Both evolutionary and exercise physiology have focused extensively on the limits to maximal physiological performance, using different approaches. This paper reviews the strengths of each field, and outlines ways in which each may benefit from dialogue with the other. The classical comparative approach employed by animal physiologists has led to the developement of statistical techniques such as phylogenetic corrections and analysis of covariance, and to an awareness of statistical pitfalls such as the misuse of ratios, particularly when correcting for body size differences. The discipline of human exercise physiology has the pragmatic advantage of being well-funded and the intellectual advantage of being tightly focused on factors influencing performance, but is hampered both by the limited insights to be gained using minimally-invasive techniques on humans and by the fact that one cannot artificially select human populations for particular traits over generations as one can fruit flies, chickens or rodents. Unhindered such restrictions, evolutionary physiology has increased our appreciation of the influence of intra- and inter-specific variation and phenotypic flexibilty on physiology. For example, invasive respiratory physiology studies in the 1980’s led to development of the concept of symmorphosis, which is still yielding insights into possible steps limiting metabolic rate. Both fields are moving towards greater understanding at molecular levels.

Development of respiratory pattern in marsupials

Peter MacFarlane and Peter Frappell

Department of Zoology, La Trobe University, Melbourne, Victoria, 3086, AUSTRALIA
(p.macfarlane@zoo.latrobe.edu.au)

Newborn marsupials are characterized by their small size and the extreme immaturity of most of their systems. Furthermore, from birth the newborn marsupial is reliant on the atmosphere of the pouch for oxygen. The lungs have, therefore, been reasoned sufficiently developed to meet the gas exchange needs of the neonate and the regulatory mechanisms and machinery of the respiratory system appropriately developed. It is now known that in one of the smallest newborns, Sminthopsis crassicaudata (birth weight ~ 17 mg) that co-ordination of the respiratory marsupials is lacking, ventilation is ineffectual and the young must rely, at least for the first few days postpartum, on the skin for gas exchange. Examination of the mechanical properties of the respiratory system in a larger newborn, Macropus eugenii (birth weight ~ 380 mg) reveals major distortion of the chest wall and the consequential reliance on the skin to supplement the lung in gas exchange. In the newborn of both species breathing is characterized by post-inspiratory pauses and is initially irregular; the irregularities disappearing during development as the lung takes on sole responsibility for gas exchange. (Funded by the ARC)

Structure and Dynamics of heat exchange at the carotid rete of Tswana Goats.

John M. Kamau, S.J. Nsoso, M. Mathaio.

Botswana College of Agriculture, Private bag 0027, Gaborone, Botswana. E-mail: jkamau@bca.bw

The carotid rete has been assumed responsible for selective brain cooling (SBC) since 1966 (2) with little evidence (1) of how it achieves this. Recent field experiments and the discovery of SBC in animals without a rete, have necessitated a re-evaluation of the role of rete in SBC. Dynamics of in-vitro heat exchange and physical measurements of carotid retie of five Tswana goats were carried out. The retie had mean length, height and width of 21.44, 8.91 and 6.04 mm respectively. However, blood vessels occupied only 0.138 mm³. The gradients of heat exchange across the rete were 0.17 /°C and 0.048 /°C at the cavernous sinus flow rate of 2 ml.min^-1 and 0.5 ml.min-¹ respectively. Flow rates in the rete and cavernous sinuses higher than 2 ml.min^-1, attenuated the temperature differences achieved across the rete. Raising the temperature of the water perfusing the cavernous sinus closer to that perfusing the rete reduced the temperature differences across it. These findings are discussed in relation to the likely situation in intact animals.

1. Kamau JMZ (1992) A comparative approach to the structural basis for brain cooling in ungulates with observations on in-vitro heat exchange. Discovery & Innovation 2:95-102.
2. Taylor CR (1966) The vascularity and possible thermoregulatory function of the horns in goats. Physiol. Zool. 39:127-139.

Thermoregulatory differences between populations of common spiny mice Acomys cahirinus from different habitats

Michael Scantlebury¹, Daniel Afik², Uri Shanas², Abraham Haim².

¹Mammal Research Institute, School of Biological Sciences, University of Bristol, Bristol BS8 1UG, UK.
²Department of Biology, University of Haifa-Oranim. Tivon 36006, Haifa, Israel.

The common spiny mouse Acomys cahirinus, of an Ethiopian origin, exists in hot arid environments. The northern-most limits of its range are in the Mediterranean regions of southern Turkey. Individuals were captured from North- and South-facing slopes (NFS and SFS) of the same valley that represent mesic and xeric habitats respectively. We hypothesized that the two populations of mice would differ in physiological capabilities, reflecting their need to cope with different environmental stresses in each habitat. We compared non-shivering thermogenesis and daily rhythms of body temperature (Tb) between the two populations. In addition, we challenged mice with increasing levels of salinity in their diet to examine their abilities to cope with increasing osmotic stress, as would occur at the end of the dry season. At the lowest (0.9%) salinity, NFS mice had higher RMR values and a larger increase in oxygen consumption as a response to noradrenaline injection (VO₂NA) than SFS mice. When the salinity was increased to 2.5% and then to 3.5%, the RMR values, minimal daily Tb, and VO₂NA of both populations decreased and slope-dependent differences diminished. Furthermore, the daily DTb of both populations and the differences in mean daily Tb between NFS and SFS populations increased. We suggest that these differences could be a result of on-going adaptive processes to different microclimatic conditions, typical of the Mediterranean region, that are a demonstrable example of evolution in action.

Accommodation to altitude in small mammals.

K. A. Hammond

Department of Biology, University of California, Riverside CA USA 92521
(khammond@ucrac1.ucr.edu)

Mammals living at high altitude must expend energy at higher rates than mammals at lower altitudes (due to cold temperatures) but they must do so in hypoxic conditions. We use deer mice (Peromyscus maniculatus) to understand physiological accommodation of altitude. Previously deer mice have been shown to be well-adapted to high altitude because of genetic differences in hemoglobin that are highly correlated with native altitude and affect short-term aerobic performance. Deer mice are also able to use phenotypic plasticity to increase size of several organ systems (cardiovascular, respiratory, and digestive) at high altitudes. It is not clear, however, whether the magnitude of the phenotypic response (for organ size and metabolic output) is affected by the site of in utero development. To examine the effect of development habitat, mice were: reared (gestation and weaning) at low altitude (340 m), reared at high altitude (3800 m), or reared at low altitude and moved to high altitude as adults (acclimation). While high-altitude acclimation results in larger organ sizes and blood oxygen carrying capacity than in low altitude mice, in utero development appears to result in still larger cardio-respiratory organs. Despite larger organs, aerobic performance of high-altitude reared mice is only slightly higher than in high-altitude-acclimated mice, and neither is as high as in low-altitude tested mice. Clearly, even though increases in organ size are probably permissive of a greater aerobic performance, neither in utero development nor high-altitude acclimation is enough to increase aerobic performance to low-altitude levels.

Rut in an arctic cervid: body composition and homeostasis in Rangifer tarandus

P.S.Barboza & J.E.Blake

Department of Biology and Wildlife, Institute of Arctic Biology, University of Alaska Fairbanks, AK USA 99775-7000.
(ffpsb@uaf.edu)

Brief periods of plant growth intensify reproductive efforts of herbivores at high latitudes. Reindeer breed when plant growth declines in autumn. We studied 7 males (2y and older) in two herds with a total of 34 females. Two males died from acute infections of minor wounds during rut. Aggression increased as antler velvet was shed in late August. Body mass declined between September and November but did not recover through winter even though food was available ad libitum. Dominance did not affect body mass or any correlate of mass loss. Dilution space for 3H2O declined with body mass. Rates of water flux were greatest at peak mass and probably reflected high intakes of both food and drinking water. Males lost 35% of ingesta-free mass in 77d of rut which corresponded to depletion of 23% body protein and 78% body lipid. Plasma insulin and thyroxine were minimal 23d after the peak in body mass indicating a response to fasting. Maximum plasma testosterone and cortisol also followed peak mass by 23d. Plasma creatinine increased as body mass declined whereas plasma urea decreased during the initial loss of mass which suggests muscle catabolism and N conservation. Variance in plasma osmolarity and urea increased as mass declined indicating reduced homeostatic control. Polygyny in reindeer compromises survival of males through reduction of body reserves, food intake and maintenance irrespective of apparent mating success. This mating strategy ultimately selects for fecundity over survival but the proximate causes of the adverse systemic effects of rut are unclear.

Impact of Chronic Cold on Naked Mole-rat Biology

Rochelle Buffenstein # and Ryan Woodley

City College of The City University of New York, and
The University of the Witwatersrand, Johannesburg, South Africa.

# Biology Department, CCNY, 138th St and Convent Avenue, New York, NY10031
(Rochelle@harold.sci.ccny.cuny.edu)

Naked mole-rats (Heterocephalus glaber) exhibit an unusual thermoregulatory profile for they are endothermic and poikilothermic mammals. We examined physiological responses to prolonged exposure to a 5°C drop in ambient temperature (T_a; 31 and 26°C) by monitoring body composition, thermoregulation, thyroid activity and reproduction.
Cold-acclimation did not elicit changes in body composition nor NST (1.52mlO₂/g/h, cold-acclimated; 1.73mlO₂/g/h, control; P>0.05). While BAT (thermogenic activity) mitochondrial proton conductance was enhanced at 26°C, it was only half that of a cold-acclimated mouse. BMRs increased at 26°C, (0.52+0.07mlO₂/g/h to 0.78+0.29 mlO₂/g/h) and this together with a 42% decline in minimal conductance facilitated a left thermoregulatory shift.
Under simulated burrow temperatures, thyroxine (T₄; 0.39 ± 0.09ng/dl) and thyroid stimulating hormone (TSH; 1.12 ± 0.56mIU/ml) concentrations fell within the reptilian range, an order of magnitude lower than mammalian levels. This may contribute substantially to the poikilothermic thermoregulatory mode exhibited by naked mole-rats. Cold induced a typical mammalian increase in T₄ concentration (0.55 ± 0.09ng/dl).
Although very few of the females housed in the cold became pregnant, those that did exhibited lower body temperatures (T_b's) than did females housed under simulated burrow conditions. In a similar manner to that of reptiles, the lower T_b's may have caused the observed 12% extension of the gestation period and the 14% larger post-partum pup mass.
The extreme sensitivity of naked mole-rats to a 5°C drop in temperature highlights several typical endothermic and poikilothermic traits and anomalies that contribute to its restricted distribution in the warm stable confines of an underground habitat.

Thermal relations of forest shrews across an environmental gradient: absence of population differentiation

C.R. Brown & R.M. Baxter*.

Department of Zoology & Entomology, Rhodes University, P.O. Box 94, Grahamstown, South Africa. (C.Brown@ru.ac.za)
*Zoology Department, University of Fort Hare, Alice, South Africa.

Thermal relations of forest shrew (Myosorex varius) populations from three different localities were investigated. The localities, Kasouga, Alice and Hogsback, differed in altitude (20, 600 and 1750m asl), climatic conditions (subtropical, temperate and montane) and vegetation type (coastal grassland, dry eastern thorn bushveld and moist upland grassland), respectively. BMR of the Hogsback population was slightly, but not significantly, higher than the other populations. Similarly, the relationships between energy expenditure and ambient temperature below the thermal neutral zone did not differ significantly between the three populations (P = 0.064). Body temperature was quite variable in all populations and averaged between 34 and 37.5 °C. Body measurements indicated that the Hogsback population was significantly larger than the Kasouga population in head-body length and tail but had significantly smaller feet (as did the Alice population). Hogsback shrews also had longer fur (P < 0.0001), which resulted in a significantly lower thermal conductance (P = 0.023). Microhabitat measurements indicated that burrow and, to a lesser extent, runway temperatures are similar across the habitats despite large differences in ambient temperatures. We conclude that the general lack of distinct population differences in thermal physiology across the wide environmental gradient may be due to the similarity in microhabitat conditions of the shrews and that these microclimates potentially account for the broad habitat tolerance of forest shrews.

Seasonal patterns of energy and water use by a small marsupial, the bilby (Macrotis lagotis), in inland Australia

Lesley A. Gibson and Ian D. Hume

School of Biological Sciences, University of Sydney, NSW 2006, Australia
Ianhume@bio.usyd.edu.au

Bilbies or rabbit-eared bandicoots (Macrotis lagotis) were once widespread west of the Great Dividing Range but are now confined to small and widely separated colonies in western Queensland and the north of Western Australia. Bilbies are semi-fossorial, resting in deep burrows by day and foraging on the surface at night when they dig for invertebrates, bulbs and grass seeds harvested by termites. We measured field metabolic rates (FMR) and water turnover rates (WTR) of free-living bilbies in Astrebla Downs National Park in western Queensland over two winters and two summers using the doubly-labelled water technique. FMR in adult animals was predicted to be higher in winter because of increased thermoregulatory costs but was found to be higher in summer. WTR was predicted to be higher in summer because of increased evaporative losses but was found to be similar between seasons. Protection from environmental extremes in burrows evidently saves the bilby significant energy in winter and water in summer. Measured FMR was not significantly below that of temperate-zone bandicoots or of most other marsupials, perhaps because of the high energy costs of digging burrows and foraging for hypogeous food throughout the year. In contrast, measured WTR was significantly below that of temperate-zone bandicoots and most other free-living marsupials, even though the original range of bilbies included temperate regions. Current bilby refugia all lie in arid regions, where a lack of free water is no ecological barrier to the bilby but, importantly, provides a level of natural protection from exotic predators such as the red fox and feral cat.

Is the ability of small rodents to dilute their urine linked to their concentrating ability?

Ian G. van Tets¹, Carol A. Beuchat² and Susan W. Nicolson³

Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa

¹ Mitrani Department of Desert Ecology, Jacob Blaustein Institute for Desert Research and Ben-Gurion University of the Negev, Midreshet Ben-Gurion 84990 Israel
²Department of Physiology, College of Medicine, University of Arizona, Tucson AZ 85724, U.S.A.
³ Department of Zoology & Entomology, University of Pretoria, Pretoria 0002, South Africa

Concentration of urine by the mammalian kidney requires the establishment of an osmotic gradient in the renal medulla through the reabsorption of solutes from the tubular filtrate, followed by the reabsorption of water from the diluted filtrate as it passes through the collecting ducts. In the absence of antidiuretic hormone (ADH), water reabsorption does not take place, and a dilute urine is excreted. The processes of urinary concentration and dilution should therefore be fundamentally linked: species that are good concentrators should also be good diluters. We tested this hypothesis on two facultatively nectarivorous southern African rodents: the striped field mouse (Rhabdomys pumilio) and the Namaqua rock mouse (Aethomys namaquensis). We measured urine osmolality of animals fed rat chow and water (control), rat chow only, and a dilute sugar solution (0.1 M sucrose). When R. pumilio and A. namaquensis were provided with food but deprived of water, urine osmolality increased from control values of 1662 and 1548 mmol/kgH₂O, respectively, to 4915 and 3416 mmol/kgH₂O. In animals provided with only sugar water, the urine was very dilute, with osmolalities averaging 30-40 mmol/kgH₂O in both species. This demonstration of the ability of these two species to both concentrate and dilute their urine has provided us with the first experimental evidence clearly supporting the hypothesis that these two abilities are linked.

Foraging challenges of colobine monkeys: Influence of nutrients and secondary compounds in different environments

C.A. Chapman

University of Florida, USA

Foraging primates face demanding challenges in meeting their nutritional requirements and when humans modify the landscape through activities such as logging or forest fragmentation, these challenges increase dramatically. Failure to meet these requirements has direct consequences on reproduction and survival. Here, we describe the diet of endangered red colobus (Procolobus badius) in a number of undisturbed habitats, in an area that have been selectively logged 30 years ago, and in a forest fragment. These monkeys digest their food in much the same way as do ruminants and have an enlarged sacculated forestomach for microbial fermentation. We found that colobine biomass varied among sites from 191 to 2675 kg.km^-2 and was related to the average protein to fiber ratio of mature leaves of the 20 most abundant tree species at each site. The presence of alkaloids, saponins, or cynogenic glycosides seems to have little influence on diet selection; in fact the most preferred plant species for one population had the greatest amount of cynogenic glycosides. Evidence suggests that mineral content had a strong impact on diet selection and possibly influenced population size.

Physiological signals used in detecting dietary toxins

William J. Foley

Division of Botany and Zoology, Australian National University Canberra ACT 0200 Australia
(william.foley@anu.edu.au)

Browsing mammals encounter a diverse range of plant secondary metabolites (PSMs) in most, if not all, foods on which they feed. Avoidance of PSMs in the diet is hardly likely to be a realistic strategy if, by doing so, animals exclude the vast majority of available plants from the diet. Instead we need to focus on understanding the physiological mechanisms by which how animals detect and regulate their intake of PSMs and the way that these signals are linked to a learning framework. Folivorous marsupials eating Eucalyptus foliage regulate their feeding so as not to exceed a threshold of intake of formylated phloroglucinol compounds. These compounds are not highly toxic but presumably lead to cell damage and release of serotonin. Administration of serotonin receptor (5HT₃) antagonists partially ameliorate the antifeedant effects. These effects can be linked with strong flavours in the food (i.e. volatile terpenes) to form conditioned flavour aversions that can guide future food choices. Not all PSMs cause these effects. Other bitter tasting PSMs (e.g. salicin) may exert no post-ingestive effects but reduce meal size without leading to the formation of conditioned flavour aversions.

Influence of leafy and woody browse on heat increment of feeding and methane production.

Robert G. White and James P. Lawler.

Large Animal research Station, University of Alaska Fairbanks, Fairbanks, Alaska 99775. USA. (ffrgw@uaf.edu: Jim_Lawler@nps.gov.us)

Before leafy and woody browse can be digested and metabolized, the anti-herbivore attributes of plant secondary compounds must be detoxified either in the gut or the liver. Detoxification occurs at an energy cost. In ruminants, browse is thought to inhibit methane (CH₄) production. Hence, some of the detoxification energy costs, measured as an elevation in the heat increment of feeding (HIF), could be offset by lower CH₄ production. To test this hypothesis, we used gas exchange to estimate energy expenditure (EE), HIF and CH₄ production in muskoxen (Ovibos moschatus) given a single test meal (at 10g/kg.75) composed of hay mixed with one of three browse species (Willow: Salix alaxsensis, S. pulchra, Birch: Betula nana). Measurement of HIF with a single meal approach (sensu thermic effect of food in humans) was complicated by residual HIF of the previous meal. A corrected analysis indicated that HIF of the hay was at expected levels (18% GE, 29% ME). Methane production however was low (2.5% GE) compared with hay fed at maintenance to cattle (8.6% GE). Dietary browse, whether leafy or woody, affected the kinetics of HIF. Dietary birch supplements decreased peak amplitude (Ap) of the thermogenic response curve, resulting in a lower HIF. Willow added to hay diets increase Ap of the thermogenic response curve, resulting in an increased HIF. Methane production declined when woody browse exceeded 20% of the meal. Leafy browse had variable effects on CH₄ production. Compared to willows, birch is not considered preferred forage of muskoxen, yet it yielded energy savings in HIF and CH₄. Factors that may be more important than HIF and CH₄ to selection or avoidance of birch include emetic effects, protein complexing, and changes in fermentation and rate of passage of ingesta that result in lowered digestibility. Effect of browse on HIF was greater than on CH₄ production, in part due to the generally low CH₄ production of muskoxen.

The Extra-Uterine Development of the Pulmonary Surfactant System in the Tammar Wallaby, Macropus eugenii

Natalie J. Miller, Sandra Orgeig, Russell V. Baudinette and Christopher B. Daniels

Dept of Environmental Biology, University of Adelaide, Adelaide SA 5005, AUSTRALIA

Marsupials are born at an early stage of development and are adapted for future development inside the pouch. Whether the pulmonary surfactant system is fully established at this altricial stage is unknown. This study correlates the presence of the surfactant proteins (SP-A, SP-B and SP-D) using immunohistochemistry with the ex-utero development of the lung in the Tammar wallaby, Macropus eugenii, and also determines the control of phosphatidylcholine (PC) secretion from developing alveolar type II cells. All three surfactant proteins were found at the site of gas exchange in the lungs of joeys at all ages, even at birth when the lungs are in the early stages of the terminal air-sac phase. Co-cultures of alveolar type II cells and fibroblasts were isolated from lungs of 30 and 70 day old joeys and incubated with the hormones, dexamethasone (10 µM), prolactin (1 µM) or triiodothyronine (100 µM), or the autonomic secretagogues, isoproterenol (100 µM) or carbamylcholine chloride (100 µM). Basal PC secretion was greater at 30 days of age than at 70 days. Co-cultures responded to all five agonists at 30 days, but only the autonomic secretagogues caused a significant increase in PC secretion at 70 days of age. This demonstrates that as the cells mature, their activity and responsiveness is reduced. The presence of the surfactant proteins at the site of gas exchange at birth suggests that the system is fully functional. It appears that surfactant development is coupled with the terminal air-sac phase of lung development rather than birth, the length of gestation or the onset of airbreathing.

Supported by the Australian Research Council

Natural Entrainment of Circadian Rhythms in the Arctic ground squirrel, Spermophilus parryii

Timothy J. Martin and Brian M. Barnes

Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775.

Abdominally implanted temperature loggers and light-sensitive radio collars were used in the field to measure circadian rhythms of the Arctic ground squirrel (Spermophilus parryii) during the active season, including periods with 24 hours of daylight. Preliminary observations and telemetry data show that squirrels are not above ground to observe rapid light-dark (LD) transitions produced by dawn and dusk. The classical phase response model for circadian entrainment by LD pulses cannot explain how squirrels entrain to the natural LD cycle. The role of other aspects of light as potential zeitgebers is presently being investigated.

Faecal Hormonal Profiles During the Reproductive Cycle, Pregnancy and Lactation in Cricetomys emini (Rodentia: Cricetidae).

M. Jean Malekani

Department of Biology, Faculty of Science, University of Kinshasa, Democratic Republic of Congo.

Cricetomys emini, commonly called cricetoma or improperly named giant rat, is an endemic African rodent of big size (1.4 Kg), traditionally hunted for food in several places where it is still occurring. Its farming can be a good source of meat for many people in Africa who are suffering from hunger and malnutrition. In addition, rearing this species can help to preserve it from overhunting and eventual disappearance and to maintain fauna biodiversity in the concerned ecosystem. Although this rodent has been reproduced with some success in captivity at the University of Kinshasa in Democratic Republic of Congo its reproductive biology is not well known. Attempts to breed this rodent on a large scale have not been successful because detailed knowledge on their reproductive biology is still scanty and sometimes incorrect. The aim of the present study is to describe and re-evaluate the reproductive pattern in Cricetomys emini in terms of occurrence, duration and! cyclicity (if any), mode of ovulation (spontaneous or induced), detection and exact lenght of pregnancy, time and duration of postpartum oestrus, time of oestrus re-establishment after weaning. Sex steroid metabolites (progesterone, oestradiol) will be measured in blood, urine and faecal samples collected from females at different physiological stages. These samples will be prepared (extraction) for thin layer chromatography (TLC), high performance liquid chromatography (HPLC), mass spectrometry (MS) and serum assays. The temporal profiles of breeding and nonbreeding females will be statistically compared and pregnancy rate (in breeding females) will be recorded. The data will be analysed to characterise the normal hormonal profiles during the reproductive cycle, pregnancy and lactation. The reproductive parameters determined will help to enhance the productivity of the rodent in captivity.

Response of blubber lipid chemistry to a low and variable food supply in the Bowhead whale.

Tamara L. Mau and Michael A. Castellini

Institute of Marine Science, University of Alaska Fairbanks, AK 99775

The lipid rich blubber layer of baleen whales serves as an important energy store. Changes in the relative thickness and lipid content of blubber are indicative of its nutritional status and body condition. Most whales fatten seasonally in response to a changing food supply and energetic demands associated with other functions of blubber including insulation, adjusting buoyancy and streamlining. The Bowhead whale has the thickest blubber of all whales, ranging from 10-50 cm, which extends beyond the thickness necessary for thermoregulation. Thus, overinsulation may be a trade-off for an increase in energy reserves, which provides a buffer during periods of low food supply.
We measured blubber thickness at six sites and blubber quality at six sites and five depths in Bowhead whales as they migrated past Point Barrow, AK in both spring and fall. We looked at factors that could affect blubber thickness and quality by comparing samples across season, age, sex and reproductive status. Blubber thickness was positively correlated and lipid content negatively correlated with total body length. Mean lipid content ranged from 68-87% and varied by both site and depth. Season was an important factor and lipid contents were generally higher in fall than in spring. Middle depths were high in lipid and stable across season, perhaps serving as a long-term reserve, whereas inner depths were quite variable and are probably the most important for active fat utilization.

Comparison of rumen fill and rate of passage in reindeer and muskoxen fed a common diet: Digestive strategies and competitive interactions.

Donald E. Spalinger1, Robert G. White2 and Pamela Groves2.

1 Department of Biology, University of Alaska Anchorage and Alaska Department of Fish and Game, Anchorage, AK 99518
2 Large Animal Research Station, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks AK 99775

Caribou and muskoxen are potentially competitive foragers, yet little is known of the way they digest common food types, information we must have to interpret diet use and preference in northern ecosystems. We hypothesized that reported differences in rumen fill and passage rates between caribou/reindeer (85kg) and muskoxen (250kg) are a function of diet and level of intake, and not a function of difference between an intermediate feeder and a grazer, sensu Hoffman. We fed a common diet (25% chopped Brome hay/ 75% concentrate pellets) at four levels of DM intake (1.3 - 3.3% BW) to rumen-cannulated reindeer (RD, 2 ad. females) and muskoxen (MO, 2 cast. males). Rumen DM fill (RDF, g/kgBW), liquid fill (RLF, l/kg BW), liquid passage rate (LPR, /h) and liquid outflow (LO, ml/h) were determined with pulsed intraruminal doses of Co-EDTA. Relative rumen fill was not different between RD and MO (RDF 13.2v14.0) (RLF 135v133), contrary to the grazer-browser hypothesis of Hoffman. T! he absolute difference in fill (RD<MO) was proportional to BW differences. DM fill/DM intake for RD (0.57) was less than MO (0.81 P<0.05). In absolute units, RDF (kg) increased with intake (kg/d) in separate regressions for RD and MO. This contrasted with absolute rumen liquid fill. Absolute RLF (l) for RD was independent of intake; whereas a linear increase was noted for MO. LPR of RD exceeded MO (0.112v0.076, P<0.05). LPR increased with intake in RD but not in MO. Although LO for RD was less than MO (1115v2043, P<0.01), a common interspecies regression related LO (Y) to DM intake (X): Y=358X+434 (R²=0.46). Liquid flow rate drives much of the passage of particulate matter from the rumen, thus DM flow likely parallels liquid flow. Since LPR of RD>MO, particulate matter of this diet should have a longer relative residence time in MO; therefore we should expect MO to digest fiber more efficiently (i.e. more completely) than RD when feeding at similar intake rate! s. Further, since LPR increases with DM intake in RD, we expect ruminal digestion of particulate matter to vary with intake in RD but to remain relatively constant with intake in MO.

Does insulin affect meal size and feeding frequency during down-regulation of food intake in winter?

Raphaela Stimmelmayr and Robert G White.

Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775.

Voluntary food intake (VFI) of caribou and reindeer is down-regulated in winter, and feeding is characterized by small, regular meals during daylight and irregular and sometimes large nighttime meals. Whereas daytime meal size approximates the energy deficit incurred since the previous meal, suggesting a role for insulin and glucose in appetite control, the occasional oversized nighttime meals suggests periodic deregulation of appetite. We hypothesized that nocturnal melatonin secretion could upset the meal size- intermeal interval mechanism by an effect on insulin secretion or a decline in sensitivity to insulin at night. In the present study a low daily insulin dose resulted in a slight rise in circulating levels of insulin and lactate in 5 pregnant female reindeer compared with 5 control animals given isotonic saline. We expected that this insulin effect would result in a more regular feeding throughout the day, and possibly would result in a decline in VFI. Exogenous! insulin prevented an up-regulation of VFI during a warming trend, and, tended to counter a linear decline in body mass and backfat depth (measured by ultra-sound) typified by control animals. Effects of exogenous insulin on feeding behavior were small, and did not eliminate daytime-nighttime differences in meal size and frequency of feeding. Thus, as judged by its affect on VFI during the warming trend, insulin exerts a role over VFI, but how strongly insulin controls meal size in short-term appetite regulation was not answered by this study. We did not predict the influence of insulin over energy retention as judged by trends in backfat thickness. We suspect that chronically increased circulating levels of insulin may stimulate the Cori Cycle resulting in both the conservation of glucose carbon and provisioning reducing units (NADPH) for lipid synthesis through the Pentose Phosphate Cycle. In the wild a ready availability of highly preferred lichens, frozen mushrooms or pe! rhaps muskrat “pushups” could provide the stimulus for increased insulin secretion in winter and thus variation in insulin levels could account for some of the observed high variability in overwinter fat use and conservation in caribou.