Craig R. Jackson

Hibernation and non-shivering thermogenesis in the Hottentot golden mole (Amblysomus hottentottus longiceps)

Although heterothermy (hibernation and torpor) is a common feature among mammals, there is debate over whether it is a derived or ancestral trait relative to endothermic homeothermy. Determination of the physiological characteristics of primitive mammals is central to understanding the evolution of endothermy. Moreover, evaluation of physiological mechanisms responsible for endothermic heat production [e.g. non-shivering thermogenesis (NST)] is key to understanding how early mammals responded to historical climate changes and colonised different geographical regions. Here we investigated the capacity for NST and heterothermy in the Hottentot golden mole, a basal eutherian mammal. NST was measured as the metabolic response to injections of noradrenalin and heterothermy by recording body temperature in free-ranging animals. We found that hibernation and torpor occurred and that the seasonal phenotypic adjustment of NST capacity was similar to that found in other placental mammals. Using phylogenetically independent contrasts, we compared measured values of NST with those obtained from the literature. This showed that all variation in NST was accounted for by differences in phylogeny and not zoogeography. These findings lend support to the observation that NST and heterothermy occur in the Afrotheria, the basal placental mammalian clade. Furthermore, this work suggests that heterothermy, rather than homeothermy is a plesiomorphic trait in mammals and supports the notion that NST mechanisms are phylogenetically ancient.

Do dispersing non-reproductive female Damaraland mole-rats, Cryptomys damarensis (Rodentia: Bathyergidae) exhibit spontaneous or induced ovulation?

The Damaraland mole-rat is a eusocial, subterranean rodent that exhibits a seasonal breeding. Non-reproductive females show physiological suppression of reproduction whilst in the confines of the natal colony. This study set out to investigate whether dispersing female Damaraland mole-rats exhibit induced or spontaneous ovulation. Fifteen non-reproductive females were removed from their natal colonies and housed individually for a period of 6 weeks. During this period urine was collected from all animals every second day. After this initial period the animals were divided into 3 groups. Females were subjected to 1 of 3 trials: a control group housed separately without a male, allowed non-physical contact, or placed in direct physical contact with vasectomized males. Urine was collected for a further 5 weeks, and urinary progesterone profiles established. All three groups showed a significant difference in urinary progesterone concentrations between the two treatment periods indicating initiation of follicular development in all animals following removal from the colony. Histological results further revealed that at least one animal in the control group and five of the six animals in the vasectomized group had corpora lutea present in the ovaries showing that ovulation has taken place. All groups had similar numbers of Graafian follicles, indicating that all females were likely to ovulate in the near future. This finding suggests that females are capable of spontaneous ovulation, but the act of coitus may advance the onset of ovulation in this arid dwelling mole-rat.

IS THE NATAL MOLE-RAT (CRYPTOMYS HOTTENTOTUS NATALENSIS) A SPONTANEOUS OR INDUCED OVULATOR?

Abstract The Natal mole-rat is a social subterranean rodent that exhibits seasonal reproduction. Nonreproductive females disperse from the natal colony and pair up with unrelated males to establish new colonies. This study set out to determine whether dispersing female Natal mole-rats are induced or spontaneous ovulators. Twelve nonreproductive females removed from natal colonies during breeding season were housed individually. Urine was collected for a period of 5 weeks. Females were subjected to 1 of 3 trials: housed separately without a male, allowed only chemical contact but not physical contact with unvasectomized males, and placed in direct contact with 4 vasectomized males. Urine was collected for a further 5 weeks, and urinary progesterone profiles established. Females housed in direct contact with males exhibited heightened progesterone concentrations and corpora lutea in the ovaries. The act of coitus appears necessary for ovulation to occur in the females despite the fact that males were not capable of fertilization.

Managing the ranging behaviour of African wild dogs (Lycaon pictus) using translocated scent marks

Abstract Context. Conflict between large carnivores and livestock outside the boundaries of wildlife areas frequently results in losses to both livestock and predator populations. The endangered African wild dog (Lycaon pictus Temminck, 1820) is wide ranging and unrestricted by conventional fences, thereby posing a major challenge to conservation managers. Wild dogs are territorial and communicate residence using scent marks. Simulating the presence of other wild dogs using translocated foreign scent marks may therefore represent a means to manage wild dog ranging behaviour. Aims. To investigate the effectiveness of using targeted scent-mark deployments to signal a wild dog pack to return to their frequented range within the safety of a protected area. Methods. We report on the ranging behaviour of a wild dog pack reintroduced into a wildlife area in Botswana with no recent history of resident wild dogs. We describe daily movements by the free-ranging introduced pack and compare these to moves following targeted deployment of scent marks when the wild dog pack had ranged close to or outside the boundaries of the protected area. Key results. Targeted foreign scent-mark exposure resulted in the pack moving closer to the geometric centre of its range. The mean distance travelled the day after exposure was significantly greater than the distance travelled the previous day and the mean daily distance moved during the study period. Conclusions. Targeted exposure to foreign scent marks proved to be a viable alternative to recapturing dogs that had ranged beyond the boundaries of the wildlife area. Implications. This novel approach to managing free-ranging carnivores utilises biologically relevant signals and holds potential not only for the conservation of African wild dogs, but also for other territorial species.

Seasonal energetics of the Hottentot golden mole at 1500 m altitude.

Winter is an energetically stressful period for small mammals as increasing demands for thermoregulation are often coupled with shortages of food supply. In sub-tropical savannah, Hottentot golden moles (Ambysomus hottentottus longiceps) forage throughout the year and for long periods of each day. This may enable them to acquire sufficient resources from an insectivorous prey base that is both widely dispersed and energetically costly to obtain. However, they also inhabit much cooler regions; how their energy budgets are managed in these areas is unknown. We measured the daily energy expenditure (DEE), resting metabolic rate (RMR) and water turnover (WTO) of free-living golden moles during both winter and summer at high altitude (1500 m). We used measurements of deuterium dilution to estimate body fat during these two periods. DEE, WTO and body mass did not differ significantly between seasons. However, RMR values were higher during the winter than the summer and, in the latter case were also lower than allometric predictions. Body fat was also higher during the winter. Calculations show that during the winter they may restrict activity to shorter, more intense periods. This, together with an increase in thermal insulation, might enable them to survive the cold.

The effect of alternative forms of hunting on the social organization of two small populations of lions Panthera leo in southern Africa

African lion Panthera leo populations have declined as a result of various anthropogenic factors, and most extant populations are small, which further compromises their persistence. Lions in unfenced areas are more exposed to illegal hunting, snaring and poisoning, and populations in fenced reserves are subject to population control by removal of selected individuals from particular age and sex classes. During 2000–2011 19 lions from the mostly unfenced Northern Tuli Game Reserve in Botswana were shot, snared or poisoned. By contrast, only one lioness was shot outside the fenced Venetia Limpopo Nature Reserve 10 km away, in South Africa, where 29 lions were trophy hunted or culled. We found that the mean population size, sex ratio and litter size were the same for both reserves but population density, pride size and cub survival rate were significantly higher in the fenced reserve. The size of the population in Northern Tuli was constrained by a high rate of indiscriminate anthropogenic mortality, with 94.7% of adult mortality occurring outside the reserve. The different forms of anthropogenic suppression in evidence at the two reserves resulted in different population-level responses, which will ultimately affect population viability. As conservation strategies are attempting to remove fences and establish larger conservation areas, this study indicates how fences can influence population dynamics in areas where human presence threatens large carnivores.

Does altitudinal difference modulate the respiratory properties in subterranean rodents' (Cryptomys hottentotus mahali) blood?

Do burrowing mammals that naturally experience hypoxic and hypercapnic conditions exhibit modifications to the blood chemistry at high altitudes? We investigated two populations of the Lesotho mole-rat living at different altitudes in the highlands of the Drakensberg. There was no significant difference between the specimens from 3200 and 1600 m in mean red blood cell count (RCC=8.9x10(6)+/-1.6x10(6) vs. 8.4x10(6)+/-0.95x10(6) mm3, respectively) or packed red cell volumes (haematocrit=0.51+/-0.06 vs. 0.49+/-0.05, respectively). However, blood haemoglobin (Hb) concentration was significantly higher in the high altitude than in the low-altitude specimens (178+/-9 vs. 160+/-16 g/l). The oxygen equilibrium curves of thawed whole blood showed no displacement to the left in the animals sampled at the higher elevation. The data indicate that the oxygen-transporting properties of mole-rat blood do not change markedly with increased elevation and that burrowing mammals are a priori hypoxia-adapted.

Heading for the hills: risk avoidance drives den site selection in African wild dogs.

Compared to their main competitors, African wild dogs (Lycaon pictus) have inferior competitive abilities and interspecific competition is a serious fitness-limiting factor. Lions (Panthera leo) are the dominant large carnivore in African savannah ecosystems and wild dogs avoid them both spatially and temporally. Wild dog young are particularly vulnerable and suffer high rates of mortality from lions. Since lions do not utilize all parts of the landscape with an equal intensity, spatial variation in lion densities can be exploited by wild dogs both during their general ranging behaviour, but more specifically when they are confined to a den with vulnerable young. Since patches of rugged terrain are associated with lower lion densities, we hypothesized that these comparatively safe habitats should be selected by wild dogs for denning. We investigated the relationship between the distribution of 100 wild dog den sites and the occurrence of rugged terrain in four wild dog populations located in Tanzania, Zimbabwe and South Africa. A terrain ruggedness index was derived from a 90 m digital elevation model and used to map terrain ruggedness at each site. We compared characteristics of actual and potential (random) den sites to determine how wild dogs select den sites. The distributions of wild dog dens were strongly associated with rugged terrain and wild dogs actively selected terrain that was more rugged than that available on average. The likelihood of encountering lions is reduced in these habitats, minimizing the risk to both adults and pups. Our findings have important implications for the conservation management of the species, especially when assessing habitat suitability for potential reintroductions. The simple technique used to assess terrain ruggedness may be useful to investigate habitat suitability, and even predict highly suitable denning areas, across large landscapes.

Ecological variables governing habitat suitability and the distribution of the endangered Juliana's golden mole

ABSTRACT Julianas golden mole (Neamblysomus julianae) occurs in three isolated populations in the northeastern parts of South Africa. This cryptic species is not evenly distributed throughout its restricted range and appears to have very specific habitat requirements. Its endangered status reflects the necessity for a conservation management programme, which to date has not been comprehensive. A primary hindrance to such initiatives has been the lack of information pertaining to its habitat requirements. We assessed various soil and vegetation parameters, at each population site, in areas where the animals were found to be present or absent. A multiple logistic regression model highlighted the importance of soil hardness (governed by soil particle size distribution), in combination with the cover provided by trees, as the two ecological factors that best explained habitat suitability for Julianas golden mole at the three localities. An IndVal analysis failed to identify any plant species that could reliably act as an indicator of habitat suitability for this fossorial mammal. These results have important implications for the conservation of the species.

The effect of relatedness and pack size on territory overlap in African wild dogs

BackgroundSpacing patterns mediate competitive interactions between conspecifics, ultimately increasing fitness. The degree of territorial overlap between neighbouring African wild dog (Lycaon pictus) packs varies greatly, yet the role of factors potentially affecting the degree of overlap, such as relatedness and pack size, remain unclear. We used movement data from 21 wild dog packs to calculate the extent of territory overlap (20 dyads).ResultsOn average, unrelated neighbouring packs had low levels of overlap restricted to the peripheral regions of their 95% utilisation kernels. Related neighbours had significantly greater levels of peripheral overlap. Only one unrelated dyad included overlap between 75%-75% kernels, but no 50%-50% kernels overlapped. However, eight of 12 related dyads overlapped between their respective 75% kernels and six between the frequented 50% kernels. Overlap between these more frequented kernels confers a heightened likelihood of encounter, as the mean utilisation intensity per unit area within the 50% kernels was 4.93 times greater than in the 95% kernels, and 2.34 times greater than in the 75% kernels. Related packs spent significantly more time in their 95% kernel overlap zones than did unrelated packs. Pack size appeared to have little effect on overlap between related dyads, yet among unrelated neighbours larger packs tended to overlap more onto smaller packs’ territories. However, the true effect is unclear given that the model’s confidence intervals overlapped zero.ConclusionsEvidence suggests that costly intraspecific aggression is greatly reduced between related packs. Consequently, the tendency for dispersing individuals to establish territories alongside relatives, where intensively utilised portions of ranges regularly overlap, may extend kin selection and inclusive fitness benefits from the intra-pack to inter-pack level. This natural spacing system can affect survival parameters and the carrying capacity of protected areas, having important management implications for intensively managed populations of this endangered species.