Universal DNA methylation age across mammalian tissues

Aging, often considered a result of random cellular damage, can be accurately estimated using DNA methylation profiles, the foundation of pan-tissue epigenetic clocks. Here, we demonstrate the development of universal pan-mammalian clocks, using 11,754 methylation arrays from our Mammalian Methylation Consortium, which encompass 59 tissue types across 185 mammalian species. These predictive models estimate mammalian tissue age with high accuracy (r > 0.96). Age deviations correlate with human mortality risk, mouse somatotropic axis mutations and caloric restriction. We identified specific cytosines with methylation levels that change with age across numerous species. These sites, highly enriched in polycomb repressive complex 2-binding locations, are near genes implicated in mammalian development, cancer, obesity and longevity. Our findings offer new evidence suggesting that aging is evolutionarily conserved and intertwined with developmental processes across all mammals.

Differential locomotor activity responses to day-time light intensity in juvenile and adult solitary Cape mole-rats, Georychus capensis (Rodentia: Bathyergidae)

The Cape mole-rat (Georychus capensis) is a solitary, strictly subterranean rodent that is responsive to light and entrains to photic cues despite having a reduced visual system. Circadian entrainment is maintained throughout life, but age can alter the amplitude of the response and re-entrainment time. Mole-rats are long-lived for their size which raises questions regarding the robustness of their circadian rhythms and how impacts their locomotor activity rhythms. The locomotor activity rhythms of juvenile and adult Cape mole-rats were investigated. They were exposed to pre-experimental and post-experimental control cycles under fluorescent lights, six 12 h light:12 h dark cycles of decreasing intensities and a constant dark cycle (DD). All animals exhibited more activity during the dark phases of all light regimes. Juveniles were more active than adults and displayed more variable activity during both the light and dark phases. Adults exhibited relatively stable levels of activity under all experimental conditions, whereas juvenile activity decreased as the light intensity was reduced. The amplitude of Cape mole-rat rhythms was consistently low, but similar across light regimes and between adults and juveniles. Cape mole-rats have functional circadian systems, are primarily nocturnal and respond differentially to light intensity depending on their age. Light intensity does not affect the locomotor activity responses of Cape mole-rats in a predictable manner, and could indicate more complex interactions with light wavelengths. The circadian systems of juveniles appear to be more sensitive than those of adults, although the mechanism of the light response remains unclear.

Octopus bimaculoides' arm recruitment and use during visually evoked prey capture

Octopus' limb hyper-redundancy complicates traditional motor control system theory due to its extensive sensory inputs, subsequent decision-making, and arm coordination. Octopuses are thought to reduce flexibility control complexity by relying on highly stereotypical motor primitives (e.g., reaching^1-4 and crawling⁵) and multi-level processes to coordinate movement,^6,7 utilizing extensive peripheral nervous system (PNS) processing.^2,8,9 Division of labor along the anterior-posterior axis¹⁰ and limb specialization of the four anterior arms in T-maze food retrieval¹¹ further simplify control. However, specific arm recruitment and coordination during visually guided reaching behavior remains poorly understood. Here, we investigated visually evoked Octopus bimaculoides' prey capture capabilities^12,13 by eliciting and examining prey-specific arm recruitment. When striking crabs, octopuses preferred synchronous arm recruitment, while sequential arm recruitment with a characteristic swaying movement is employed for shrimp. Such behavioral selection aligns with specific prey escape strategies and the octopus' flexible arm biomechanical constraints. Although side bias existed, we found significant bilateral symmetry, with one side being functionally a mirror of the other rather than anterior arm use being functionally equal and differing to posterior arm use. Among arms, the second limb is unequivocally dominant for goal-directed monocularly driven prey capture. Although the eight arms share gross anatomy and are considered equipotential,^10,14 such arm use for specific actions could reflect subtle evolutionary adaptations. Finally, we quantitatively show, corroborating earlier observations,^10,15 that octopuses employ a dimension reduction strategy by actively deciding to recruit adjacent arms over other available arms during either sequential or synchronous visually evoked prey attack.

The endocrine control of reproductive suppression in an aseasonally breeding social subterranean rodent, the Mahali mole-rat (Cryptomys hottentotus mahali)

Cooperative behaviour, sociality and reproductive suppression in African mole-rats have been extensively studied. Nevertheless, endocrine correlates of some species of social mole-rats have been neglected, and these species may hold the key to understanding the behavioural and physiological complexity that allows the maintenance of social groups in African mole-rats. In this study, we investigated endocrine correlates implicated in the suppression of reproduction and cooperative behaviours, namely glucocorticoids (a stress-related indicator) through faecal glucocorticoid metabolites (fGCMs), plasma testosterone (an indicator of aggression) and plasma prolactin in the Mahali mole-rat (Cryptomys hottentotus mahali) across reproductive classes (breeding females and males, non-breeding females and males) and season (wet and dry). Breeders possessed higher levels of testosterone than non-breeders. In reproductively suppressed non-breeding females, fGCMs were significantly higher than in breeders. Furthermore, an adrenocorticotropic hormone stimulation test (ACTH challenge test) on both male and female non-breeders revealed that female non-breeders show a more significant response to the ACTH challenge than males. At the same time, plasma prolactin levels were equally elevated to similar levels in breeding and non-breeding females. Chronically high levels of prolactin and fGCM are reported to cause reproductive suppression and promote cooperative behaviours in non-breeding animals. Furthermore, there was a negative relationship between plasma prolactin and progesterone in non-breeding females. However, during the wet season, a relaxation of suppression occurs through reduced prolactin which corresponds with elevated levels of plasma progesterone in non-breeding females. Therefore, prolactin is hypothesised to be the primary hormone controlling reproductive suppression and cooperative behaviours in non-breeding females. This study provides new endocrine findings for the maintenance of social suppression in the genus Cryptomys.

Species limits and phylogeographic structure in two genera of solitary African mole-rats Georychus and Heliophobius

African mole-rats (Bathyergidae) are an intensively studied family of subterranean rodents including three highly social and three solitary genera. Although their phylogenetic interrelations are clear, genetic diversity and the number of species within each genus is much less certain. Among the solitary genera, Heliophobius and Georychus were for a long time considered as monotypic, but molecular studies demonstrated strong phylogeographic structure within each genus and proposed that they represent complexes of cryptic species. The present study re-evaluates their internal genetic/phylogenetic structure using a combination of methodological approaches. We generated datasets of one mitochondrial and six specifically selected nuclear markers as well as of a large number of double digest restriction site associated (ddRAD) loci and then applied species delimitation analyses based on the multispecies coalescent model or clustering on co-ancestry matrices. The population structure was largely congruent across all analyses, but the methods differed in their resolution scale when determining distinct gene pools. While the multispecies coalescent model distinguished five Georychus and between eleven to thirteen Heliophobius gene pools in both Sanger sequenced and ddRAD loci, two clustering algorithms revealed significantly finer or coarser structure in ddRAD based co-ancestry matrices. Tens of clusters were distinguished by fineRADstructure and one (in Georychus) or two clusters (in Heliophobius) by Infomap. The divergence dating of the bathyergid phylogeny estimated that diversification within both genera coincided with the onset of the Pleistocene and was likely driven by repeated large-scale climatic changes. Based on this updated genetic evidence, we suggest recognizing one species of Georychus and two species of Heliophobius, corresponding to a northern and southern major lineage, separated by the Eastern Arc Mountains. Yet, the final taxonomic revision should await integrated evidence stemming from e.g.. morphological, ecological, or behavioral datasets.

Zika Virus Infection of Pregnant Ifnar1-/- Mice Triggers Strain-Specific Differences in Fetal Outcomes

Zika virus (ZIKV) is a flavivirus that causes a constellation of adverse fetal outcomes collectively termed congenital Zika syndrome (CZS). However, not all pregnancies exposed to ZIKV result in an infant with apparent defects. During the 2015 to 2016 American outbreak of ZIKV, CZS rates varied by geographic location. The underlying mechanisms responsible for this heterogeneity in outcomes have not been well defined. Therefore, we sought to characterize and compare the pathogenic potential of multiple Asian-/American-lineage ZIKV strains in an established Ifnar1-/- pregnant mouse model. Here, we show significant differences in the rate of fetal demise following maternal inoculation with ZIKV strains from Puerto Rico, Panama, Mexico, Brazil, and Cambodia. Rates of fetal demise broadly correlated with maternal viremia but were independent of fetus and placenta virus titer, indicating that additional underlying factors contribute to fetal outcome. Our results, in concert with those from other studies, suggest that subtle differences in ZIKV strains may have important phenotypic impacts. With ZIKV now endemic in the Americas, greater emphasis needs to be placed on elucidating and understanding the underlying mechanisms that contribute to fetal outcome. IMPORTANCE Zika virus (ZIKV) transmission has been reported in 87 countries and territories around the globe. ZIKV infection during pregnancy is associated with adverse fetal outcomes, including birth defects, microcephaly, neurological complications, and even spontaneous abortion. Rates of adverse fetal outcomes vary between regions, and not every pregnancy exposed to ZIKV results in birth defects. Not much is known about how or if the infecting ZIKV strain is linked to fetal outcomes. Our research provides evidence of phenotypic heterogeneity between Asian-/American-lineage ZIKV strains and provides insight into the underlying causes of adverse fetal outcomes. Understanding ZIKV strain-dependent pathogenic potential during pregnancy and elucidating underlying causes of diverse clinical sequelae observed during human infections is critical to understanding ZIKV on a global scale.

A non-invasive assessment of essential trace element utilization at different trophic levels in African wildlife

The complex relationships that exist between terrestrial mammals and their habitats make African ecosystems highly interactive environments. Anthropogenic activities including climate change have altered geochemical cycles, which influence nutrient availability and deficiency at local, regional and global scales. As synergistic and antagonistic interactions occur between essential elements at both deficiency and excess concentrations, the differences in feeding strategy between trophically distinct groups of terrestrial vertebrates are likely to influence the degree to which overall nutrient needs are met or may be deficient. The overall aim of this study was to investigate and compare quantitative differences of nine essential elements in terrestrial vertebrates occupying different trophic levels within two protected areas; Tswalu Kalahari Reserve (TKR) and Manyeleti Nature Reserve (MNR) South Africa, using faeces as an analytical matrix. Results from linear mixed effects models highlight that concentrations varied widely between individuals. Overall, measured concentrations above their respective means were evident for B and Mn in herbivores, Fe in omnivores and Cu, Co, Fe, Se and Zn in carnivores. Measured concentrations of Mo and Ni did not differ significantly between trophic groups. Although site-specific differences were evident for specific elements, measured mean concentrations of B, Co, Cu, Fe, Mo, Ni, Se and Zn were significantly higher overall at the MNR study site compared to the TKR site. This is the first study to non-invasively assess essential element concentrations across trophic levels in free ranging African wildlife species within protected areas of the savannah biome. Combined with the assessment of environmental matrices, this approach can be used as an effective diagnostic tool for the assessment of animal welfare and the management of protected areas globally.

Oxidative stress in response to heat stress in wild caught Namaqua rock mice, Micaelamys namaquensis

Modelling of anthropogenic induced climate suggests more frequent and severe heatwaves in the future, which are likely to result in the mass die-off of several species of organisms. Oxidative stress induced by severe heat stress has previously been associated with a reduction in animal cognitive performance, depressed reproduction and lower life expectancy. Little is known about the non-lethal consequences of species should they survive extreme heat exposure. We investigated the oxidative stress experienced by the Namaqua rock mouse, a nocturnal rodent, using two experimental heat stress protocols, a 6 hour acute heat stress protocol without access to water and a 3-day heatwave simulation with ad libitum water. Oxidative stress was determined in the liver, kidney and brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers of oxidative damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers of antioxidant defence. Incubator heat stress (heat and dehydration stress) was brought about by increasing the body temperatures of animals to 39-40.8 °C for 6 hours. Following incubator heat stress, significantly higher levels of MDA were observed in the liver. Dehydration did not explain the variation in oxidative markers and is likely a combined effect of thermal and dehydration stress. Individual body mass was significantly negatively correlated to kidney SOD and lipid peroxidation. A heatwave was simulated using a temperature cycle that would naturally occur during a heatwave in the species' local habitat, with a maximal ambient temperature of 38 °C. Following the simulated heatwave, SOD activity of the kidney demonstrated significantly lowered activity suggesting oxidative stress. Current heat waves in this species have the potential of causing oxidative stress. Heat and dehydration stress following exacerbated temperatures are likely to incur significant oxidative stress in multiple tissues demonstrating the importance of water availability to allow for rehydration to prevent oxidative stress.

African Naked Mole-Rats Demonstrate Extreme Tolerance to Hypoxia and Hypercapnia

Naked mole-rats are extremely tolerant to low concentrations of oxygen (hypoxia) and high concentrations of carbon dioxide (hypercapnia), which is consistent with the environment that they inhabit. Naked mole-rats combine subterranean living with living in very densely populated colonies where oxygen becomes depleted and carbon dioxide accumulates. In the laboratory, naked mole-rats fully recover from 5 h exposure to 5% O₂ and 5 h exposure to 80% CO₂, whereas both conditions are rapidly lethal to similarly sized laboratory mice. During anoxia (0% O₂) naked mole-rats enter a suspended animation-like state and switch from aerobic metabolism of glucose to anaerobic metabolism of fructose. Additional fascinating characteristics include that naked mole-rats show intrinsic brain tolerance to anoxia; a complete lack of hypoxia-induced and CO₂-induced pulmonary edema; and reduced aversion to high concentrations of CO₂ and acidic fumes. Here we outline a constellation of physiological and molecular adaptations that correlate with the naked mole-rat's hypoxic/hypercapnic tolerance and which offer potential targets for ameliorating pathological conditions in humans, such as the damage caused during cerebral ischemia.

Hind foot drumming: morphological adaptations of the muscles and bones of the hind limb in three African mole-rat species

Seismic signalling in the form of hind foot drumming plays an integral role in the communication of several species of African mole-rats (Bathyergidae). To produce these vibrational signals, alternating hind limbs strike the ground repetitively at high speeds by flexion and extension of the hip and knee. This descriptive study aimed to determine whether anatomical differences in hind limb osteology and/or musculature between drumming and non-drumming species of three Bathyergidae species could be detected. Formalin-fixed left and right hind limbs of 24 animals (N = 48) consisting of three species (n = 16 each) of two drumming species, Georychus capensis and Bathyergus suillus, and one non-drumming species, Cryptomys hottentotus natalensis, were dissected to determine the origins and insertions of individual muscles. After dissection, all soft tissue was removed by maceration. Hind limb bones, including the pelvis, were photographed, and the exact muscle origin and insertion points were electronically mapped onto the images using imaging software. On lateral view, the acetabular position was parallel to the sacrum in G. capensis, while being more ventral in position in the other two species. The shape of the femur head was spherical and the neck defined in all species. The distal shaft of the femur was gracile and the epicondyles were robust and prominent in the non-drumming C. h. natalensis compared with the drumming species. Shallow and relatively wide patellar grooves were observed in all three species. In the two drumming species, m. gracilis was single, whereas it was double in C. h. natalensis. In all three species, m. tensor fasciae latae was absent. The more dorsal positioning of the acetabulum in G. capensis may be needed to increase the stability of the spine and allow for more force to be exerted on the pelvis during drumming. It is unlikely that m. gracilis plays a role in drumming, as the singularity or doubling thereof is variable among rodents. It is additionally postulated that m. gluteus superficialis has taken the hip rotator role of m. tensor fasciae latae as it partially inserted onto the lateral fascia of the thigh. The more robust ilia, femoral shafts and tibiae observed in the two drumming species studied here are possible adaptations for hind foot drumming, as robust bones are able to withstand the additional biomechanical loading during drumming.

Evidence for contrasting roles for prolactin in eusocial naked mole-rats, Heterocephalus glaber and Damaraland mole-rats, Fukomys damarensis

Elevated prolactin (PRL) has been associated with the expression of social and cooperative behaviours in a number of vertebrate species, as well as suppression of reproduction. As social mole-rats exhibit both of these traits, PRL is a prime candidate in mediating their social phenotype. While naked and Damaraland mole-rats (NMRs and DMRs) have evolved eusociality independently within their family, both species exhibit an extreme skew in lifetime reproductive success, with breeding restricted to a single female and one or two males. Non-breeding NMRs of both sexes are physiologically inhibited from reproducing, while in DMRs only the non-breeding females are physiologically suppressed. Newly emerging work has implicated the dopamine system and PRL as a component in socially induced reproductive suppression and eusociality in NMR, but the DMR remains unstudied in this context. To investigate evolutionary convergence in the role of PRL in shaping African mole-rat eusociality, we determined plasma PRL concentrations in breeders and non-breeders of both sexes, comparing DMRs with NMRs. Among samples from non-breeding NMRs 80% had detectable plasma PRL concentrations. As a benchmark, these often (37%) exceeding those considered clinically hyperprolactinaemic (25 ng ml^-1) in humans: mean ± s.e.m.: 34.81 ± 5.87 ngml^-1; range 0.00-330.30 ng ml^-1 Conversely, 85% of non-breeding DMR samples had undetectable values and none had concentrations above 25 ng ml^-1: 0.71 ± 0.38 ng ml^-1; 0.00-23.87 ngml^-1 Breeders in both species had the expected variance in plasma PRL concentrations as part of normal reproductive function, with lactating queens having significantly higher values. These results suggest that while elevated PRL in non-breeders is implicated in NMR eusociality, this may not be the case in DMRs, and suggests a lack of evolutionary convergence in the proximate control of the social phenotype in these mole-rats.

Reproductive status-dependent kisspeptin and RFamide-related peptide (Rfrp) gene expression in female Damaraland mole-rats

Damaraland mole rats (Fukomys damarensis) are cooperatively breeding, subterranean mammals that exhibit a high reproductive skew. Reproduction is monopolised by the dominant female of the group, whereas subordinates are physiologically suppressed to the extent that they are anovulatory. In these latter animals, it is assumed that normal gonadotropin-releasing hormone secretion from the hypothalamus is disrupted. The RFamide peptides kisspeptin (Kiss1) and RFamide-related peptide-3 (RFRP-3) are considered as potent regulators of gonadotropin release. To assess whether these neuropeptides are involved in the mechanism of reproductive suppression, we investigated the distribution and gene expression of Kiss1 and Rfrp by means of in situ hybridisation in wild-caught female Damaraland mole-rats with different reproductive status. In both reproductive phenotypes, substantial Kiss1 expression was found in the arcuate nucleus and only few Kiss1-expressing cells were detected in the anteroventral periventricular nucleus (AVPV), potentially as a result of low circulating oestradiol concentrations in breeding and nonbreeding females. Rfrp gene expression occurred in the dorsomedial nucleus, the paraventricular nucleus and the periventricular nucleus. While in female breeders and nonbreeders, plasma oestradiol levels were low and not significantly different, quantification of the hybridisation signal for both genes revealed significant differences in relation to reproductive status. Reproductively active females had more Kiss1-expressing cells and a higher number of silver grains per cell in the arcuate nucleus compared to nonreproductive females. This difference was most pronounced in the caudal part of the nucleus. No such differences were found in the AVPV. Furthermore, breeding status was associated with a reduced number of Rfrp-expressing cells in the anterior hypothalamus. This reproductive status-dependent expression pattern of Kiss1 and Rfrp suggests that both neuropeptides play a role in the regulation of reproduction in Damaraland mole-rats. Enhanced long-term negative feedback effects of oestradiol could be responsible for the lower Kiss1 expression in the arcuate nucleus of reproductively suppressed females.

The impact of age-class and social context on fecal glucocorticoid metabolite levels in free-ranging male giraffes

One of the primary sources of perceived stress is the social environment of an animal and the interactions with conspecifics. An essential component of the response to a stressor is the activation of the hypothalamic-pituitary-adrenocortical axis, which results amongst others in a temporal increase in circulating glucocorticoid (GC) levels. Giraffes occur in a highly flexible fission-fusion social system and group compositions can change on a daily basis, with bulls establishing an age-related dominance hierarchy and showing a roaming strategy in the search for fertile females. The aim of this study was to non-invasively monitor the influence of different group compositions (mixed sex groups vs. all-male groups) on GC concentrations in free ranging giraffe bulls of different age classes. We collected fecal samples from free-ranging giraffe bulls for 12months in a South African Private Game Reserve to examine age- and social context-related patterns of fecal GC metabolite (fGCM) concentrations. We found that fGCM levels in giraffe bulls are age-class dependent, as well asassociated with changes in the social environment. Independently of the social setting, bulls of the youngest age class exhibited the highest fGCM levels compared to bulls of the other two older age-classes, with differences most pronounced when the bulls are associated in all-male groups. In contrast, an almost reversed picture appears when looking at the fGCM levels of sexually active individuals in mixed sex groups, where highest levels were found for the bulls in the oldest age-class, and the lowest for the bulls in the youngest age-class. The study stresses the importance to taking factors such asage-related status and social settings into account, when interpreting fGCM levels in free ranging giraffes.

Age and socially related changes in fecal androgen metabolite concentrations in free-ranging male giraffes

In many mammal species, androgen levels in males are elevated during periods of mating activity, often to facilitate aggressive behavior between males over access to fertile females. However, this pattern might be less obvious in species with a rather low male-male aggression rate, or in those that are not strictly seasonal breeders. A complex social structure, as well as additional social and environmental factors, might add more to the complexity. Here, we applied a non-invasive method to monitor fecal androgen metabolite (fAM) levels in free-ranging giraffe bulls over a period of months to examine longitudinal patterns of androgen metabolite concentrations in relation to observed male sexual behavior in different age classes. Giraffes are non-seasonal breeders, living in a fission-fusion social system and males show a roaming strategy to search for fertile females. Our results show that season has an impact on fAM levels in free-ranging giraffes, with respective steroid concentrations being higher in summer. In the presence of females, fAM levels of bulls are significantly higher compared to when found in all-male groups, with old adult bulls showing the highest fAM levels. In contrast, young adult bulls have overall slightly higher fAM levels compared to old adult bulls when residing in all male groups. Sexual behavior increases fAM levels only in old adult bulls.

The Distribution of Gastrointestinal Parasites in Two Populations of Common Mole-Rats ( Cryptomys hottentotus hottentotus)

The spread of parasites through a host population is based on the variation in behavior and immune function between individuals and is rarely uniform. We studied the gastrointestinal parasites of common mole-rats ( Cryptomys hottentotus hottentotus, Lesson 1826) from 2 sites and assessed the levels of infection based on host sex, breeding status, and season. Only nematode species were found: Neoheligmonella sp. and Mammalakis macrospiculum (Ortlepp, 1939) and a single specimen of Trichuris sp., all of which have direct life cycles. Parasite burden and species richness was greater in the mesic habitat. The abundance of Neoheligmonella sp. differed significantly between seasons, and the season of peak abundance differed between sites, perhaps due to differences in host densities between sites. In addition, parasite burden did not differ between the sexes, but breeding animals had higher infections of Neoheligmonella sp. and M. macrospiculum than non-breeding animals. This and previous studies thus suggest that the subterranean environment is beneficial in reducing parasite diversity, although the restrictions on movement may lead to certain individuals suffering higher parasite burdens.

Psychological stress affects the severity of radiation-induced acute skin reactions in breast cancer patients

Psychological stress exacerbates many pathological conditions including inflammatory skin conditions. The effect of psychological stress on acute radiation-induced skin reactions has not been documented before. Here, we aimed to explore if psychological stress could aggravate skin reaction severity in breast cancer patients. We conducted a secondary analysis of patient data obtained during a randomised, controlled clinical trial for acute radiation-induced skin reaction severity in 78 breast cancer patients. Patients were assessed three times a week during treatment. Skin reaction severity was measured using the modified Radiation-Induced Skin Reaction Assessment Scale (RISRAS) and Radiation Therapy Oncology Group grades. Stress levels were determined using a 5-point LIKERT scale to rate physical well-being, managing stress levels, house, family, work and other commitments. A total of 20 patients (26%) of the 78-patient cohort were considered stressed. Skin reaction severity in stressed patients was twice that of non-stressed patients (p < 0.001) and stressed patients were five times more likely to develop moist desquamation. Our results show that psychological stress aggravates skin reaction severity during radiation therapy. This research needs to be validated in a more rigorous manner by incorporating a validated scale such as the Distress Thermometer and Impact Thermometer in future skin trials.

Ectoparasite fauna of rodents collected from two wildlife research centres in Saudi Arabia with discussion on the implications for disease transmission

The majority of human pathogens are zoonotic and rodents play an important role as reservoirs of many of these infectious agents. In the case of vector-borne pathogens, rodent reservoirs not only act as a source of infection for vectors but also serve as hosts for the vectors themselves, supporting their populations. Current data on rodent-ectoparasite relationships is limited in Saudi Arabia, however, this is needed to assess disease risk and the relative importance of different hosts for the maintenance of vector-borne pathogen cycles. In order to provide baseline data for the region that could be used to assess zoonotic disease risk, we collected and identified 771 ectoparasite specimens (ticks, fleas and mites) from 161 rodents at two wildlife research centres in Saudi Arabia and discuss our results in the context of possible zoonotic disease risk based on the hosts and vectors present.

Microbats appear to have adult hippocampal neurogenesis, but post-capture stress causes a rapid decline in the number of neurons expressing doublecortin

A previous study investigating potential adult hippocampal neurogenesis in microchiropteran bats failed to reveal a strong presence of this neural trait. As microchiropterans have a high field metabolic rate and a small body mass, it is possible that capture/handling stress may lead to a decrease in the detectable presence of adult hippocampal neurogenesis. Here we looked for evidence of adult hippocampal neurogenesis using immunohistochemical techniques for the endogenous marker doublecortin (DCX) in 10 species of microchiropterans euthanized and perfusion fixed at specific time points following capture. Our results reveal that when euthanized and perfused within 15 min of capture, abundant putative adult hippocampal neurogenesis could be detected using DCX immunohistochemistry. Between 15 and 30 min post-capture, the detectable levels of DCX dropped dramatically and after 30 min post-capture, immunohistochemistry for DCX could not reveal any significant evidence of putative adult hippocampal neurogenesis. Thus, as with all other mammals studied to date apart from cetaceans, bats, including both microchiropterans and megachiropterans, appear to exhibit substantial levels of adult hippocampal neurogenesis. The present study underscores the concept that, as with laboratory experiments, studies conducted on wild-caught animals need to be cognizant of the fact that acute stress (capture/handling) may induce major changes in the appearance of specific neural traits.

Mammalian eusociality: a family affair

Comparative studies of two species of mole-rat are helping to clarify the ecological correlates of mammalian eusociality. Both species live in social groups composed of close kin, within which breeding is restricted to one female and one to three males. They inhabit xeric areas with dispersed, patchy food and unpredictable rainfall. During droughts, they can neither expand their tunnel systems nor disperse. In brief periods after rain the animals must cooperate and dig furiously to locate rich food patches. By living in groups, arid-zone mole-rats can take full advantage of windows of opportunity when conditions are right for burrowing. Thus, ecological factors and kin selection have apparently interacted in the evolution of eusociality in these species.

Bartonellae of the Namaqua rock mouse, Micaelamys namaquensis (Rodentia: Muridae) from South Africa

The aim of this study was to determine Bartonella prevalence and diversity in Namaqua rock mice, Micaelamys namaquensis, a species endemic to South Africa, which can attain pest status. A total of 100 heart samples collected monthly from March to December were screened for Bartonella genome presence using three primer sets targeting the citrate synthase (gltA) gene, the NADH dehydrogenase gamma subunit (nuoG) gene and the RNA polymerase β-subunit-encoding gene (rpoB). An overall prevalence of 44% was obtained, with no statistically significant differences or correlations between infection rates and rodent sex, month of capture or season of capture. Phylogenetic analysis of 34 unambiguous gltA sequences revealed the presence of three discrete Bartonella lineages in M. namaquensis, one of which corresponds to Bartonella elizabethae, a species with known zoonotic potential.

Determination of an optimal dose of medetomidine-ketamine-buprenorphine for anaesthesia in the Cape ground squirrel (Xerus inauris)

The optimal dose of medetomidine-ketamine-buprenorphine was determined in 25 Cape ground squirrels (Xerus inauris) undergoing surgical implantation of a temperature logger into the abdominal cavity. At the end of anaesthesia, the squirrels were given atipamezole intramuscularly to reverse the effects of medetomidine. The mean dose of medetomidine was 67.6 +/- 9.2microg/kg, ketamine 13.6 +/- 1.9 mg/kg and buprenorphine 0.5 +/- 0.06 microg/kg. Induction time was 3.1 +/- 1.4 min. This produced surgical anaesthesia for 21 +/- 4.2 min. Atipamezole 232 +/- 92 microg/kg produced a rapid recovery. Squirrels were sternally recumbent in 3.5 +/- 2.2 min.

Mepilex Lite dressings for the management of radiation-induced erythema: a systematic inpatient controlled clinical trial

Erythema occurs in 80-90% of women treated for breast cancer with radiation therapy. There is currently no standard treatment for radiation-induced skin reactions. This study investigates the clinical efficacy of Mepilex Lite dressings in reducing radiation-induced erythema in women with breast cancer. A total of 28 patients were recruited; of these, 24 participants presented with 34 erythematous areas of skin for analysis. When erythema was visible, each affected skin area was randomly divided into two similar halves: one half was treated using Mepilex Lite dressings, the other half with standard aqueous cream. Skin reactions were assessed by the Radiation-Induced Skin Reaction Assessment Scale. We also evaluated any potential dose build-up by the dressings using a white water phantom, the dose distribution over the breast via thermoluminescent dosimeters (TLDs) and the surface skin temperature with an infrared thermographic scanner. Mepilex Lite dressings significantly reduced the severity of radiation-induced erythema compared with standard aqueous cream (p <0.001), did not affect surface skin temperature and caused only a small (0.5 mm) dose build-up. TLD measurements showed that the inframammary fold was exposed to significantly higher doses of radiation than any other breast region (p <0.0001). Mepilex dressings reduce radiation-induced erythema.

Placentation in the Hottentot golden mole, Amblysomus hottentotus (Afrosoricida: Chrysochloridae)

The placentation of the Hottentot golden mole (Amblysomus hottentotus) has been examined using light and electron microscopy and lectin histochemistry of nine specimens at both mid and late gestation. The placentae were lobulated towards the allantoic surface and the lobules contained roughly parallel arrays of labyrinthine structures converging on a central spongy zone. At mid gestation, the arrays were composed of an inner cellular and outer syncytial trophoblast layer, the inner layer enclosing scant connective tissue and fetal capillaries. Maternal blood spaces coursed through the outer trophoblast and were lined by trophoblastic microvilli; the blood spaces were narrow in mid gestation but enlarged near term, while the inner trophoblast layer became thinner and seemed to be syncytial. These features were confirmed by transmission electron microscopy. The microvillous surfaces and dispersed cytoplasmic particles were heavily glycosylated, as shown by lectin histochemistry, and exhibited changes with maturation, particularly a loss in N-acetyl glucosamine oligomers bound by Phytolacca americana lectin on the microvilli lining the maternal blood spaces and outer trophoblast particles. A substantial yolk sac was present both in mid and late gestation stages. It was clearly unattached to the uterus in the later stages. These morphological features are discussed in relation to the phylogenetic position of Amblysomus with respect to other members of Afrosoricida and Afrotheria.

Reproductive suppression and the seasonality of reproduction in the social Natal mole-rat (Cryptomys hottentotus natalensis)

Natal mole-rats are social subterranean rodents which exhibit a reproductive division of labour. Reproduction is confined to a single breeding female and one or more males; the remainder of the colony members is reproductively suppressed by the presence of the breeding animals. Apart from the discovery that female Natal mole-rats are induced ovulators, little is known about the reproductive biology of this species. Natal mole-rats are closely related to common and highveld mole-rats, both of which are induced ovulators and seasonal breeders. We therefore postulated that reproduction in Natal mole-rats is seasonally regulated. However, the results indicate that dominant Natal mole-rats are able to reproduce in the winter as well as in the summer. Furthermore, the increment in plasma LH in response to GnRH does not show marked seasonal differences in reproductive or non-reproductive mole-rats of either sex. Nevertheless, in all reproductive categories the level of plasma LH is significantly higher in the winter than in the summer. Seasonality in plasma LH levels dissociated from seasonality in breeding seems paradoxical. Further investigations will be required to elucidate this finding. We also investigated the processes underlying socially regulated reproduction in this species by determining basal and GnRH-evoked plasma LH in reproductive and non-reproductive animals of each sex in both seasons. The results failed to identify neuroendocrine differences consistent with an inhibited reproductive state in subordinates of either sex. Thus, the present findings suggest that behavioural interactions and/or inbreeding avoidance are the principal factors underlying suppression of reproduction in subordinate Natal mole-rats.

Chromosomal phylogeny and evolution of the African mole-rats (Bathyergidae)

The subterranean African mole-rats (Family Bathyergidae) show considerable variation in their diploid numbers, but there is limited understanding of the events that shaped the extant karyotypes. Here we investigate chromosomal evolution in specimens representative of six genera and an outgroup species, the cane rat Thryonomys swinderianus, using flow-sorted painting probes isolated from the naked mole-rat, Heterocephalus glaber (2n = 60). A chromosomal phylogeny based on the cladistic analysis of adjacent syntenies detected by cross-species chromosome painting was not consistent with that obtained using DNA sequences due, in large part, to the conserved nature of the Bathyergus, Georychus and Cryptomys karyotypes. In marked contrast, the Fukomys and Heliophobius species showed extensive chromosome reshuffling, permitting their analysis by a computational approach that has conventionally been employed in comparative genomic studies for retrieving phylogenetic information based on DNA sequence or gene order data. Using the multiple genome rearrangements (MGR) algorithm and chromosomal rearrangement data detected among F. damarensis, F. darlingi, F. mechowi and the sister taxa B. janetta and Heliophobius argenteocinereus, cytogenetic support for the monophyly of Fukomys and a sister association for F. darlingi + F. damarensis was retrieved, mirroring the published sequence-based topology. We show that F. damarensis, a lineage adapted to arid and climatically unpredictable environments in Southern Africa, is characterized by a large number of fissions the fixation of which has probably been favoured by environmental factors and/or its particular eusocial structure.

Alternative reproductive tactics in male Cape ground squirrels Xerus inauris

In some animal societies, males vary in the strategies and tactics that they use for reproduction. Explanations for the evolution of alternative tactics have usually focussed on extrinsic factors such as social status, the environment or population density and have rarely examined proximate differences between individuals. Anecdotal evidence suggests that two alternative reproductive tactics occur in cooperatively breeding male Cape ground squirrels. Here we show that there is strong empirical support for physiological and behavioural differences to uphold this claim. 'Dispersed' males have higher resting metabolic rates and a heightened pituitary activity, compared with philopatric 'natal' males that have higher circulating cortisol levels. Dispersed males also spend more time moving and less time feeding than natal males. Additionally, lone males spend a greater proportion of their time vigilant and less of their time foraging than those that were in groups. The choice of whether to stay natal or become a disperser may depend on a number of factors such as age, natal group kin structure and reproductive suppression, and the likelihood of successful reproduction whilst remaining natal. Measuring proximate factors, such as behavioural and endocrine function, may provide valuable insights into mechanisms that underlie the evolution of alternative reproductive tactics.

Energetic costs of parasitism in the Cape ground squirrel Xerus inauris

Parasites have been suggested to influence many aspects of host behaviour. Some of these effects may be mediated via their impact on host energy budgets. This impact may include effects on both energy intake and absorption as well as components of expenditure, including resting metabolic rate (RMR) and activity (e.g. grooming). Despite their potential importance, the energy costs of parasitism have seldom been directly quantified in a field setting. Here we pharmacologically treated female Cape ground squirrels (Xerus inauris) with anti-parasite drugs and measured the change in body composition, the daily energy expenditure (DEE) using doubly labelled water, the RMR by respirometry and the proportions of time spent looking for food, feeding, moving and grooming. Post-treatment animals gained an average 19g of fat or approximately 25kJd-1. DEE averaged 382kJd-1 prior to and 375kJd-1 post treatment (p>0.05). RMR averaged 174kJd-1 prior to and 217kJd-1 post treatment (p<0.009). Post-treatment animals spent less time looking for food and grooming, but more time on feeding. A primary impact of infection by parasites could be suppression of feeding behaviour and, hence, total available energy resources. The significant elevation of RMR after treatment was unexpected. One explanation might be that parasites produce metabolic by-products that suppress RMR. Overall, these findings suggest that impacts of parasites on host energy budgets are complex and are not easily explained by simple effects such as stimulation of a costly immune response. There is currently no broadly generalizable framework available for predicting the energetic consequences of parasitic infection.

Intrasexual competition and sexual selection in cooperative mammals

In most animals, the sex that invests least in its offspring competes more intensely for access to the opposite sex and shows greater development of secondary sexual characters than the sex that invests most. However, in some mammals where females are the primary care-givers, females compete more frequently or intensely with each other than males. A possible explanation is that, in these species, the resources necessary for successful female reproduction are heavily concentrated and intrasexual competition for breeding opportunities is more intense among females than among males. Intrasexual competition between females is likely to be particularly intense in cooperative breeders where a single female monopolizes reproduction in each group. Here, we use data from a twelve-year study of wild meerkats (Suricata suricatta), where females show high levels of reproductive skew, to show that females gain greater benefits from acquiring dominant status than males and traits that increase competitive ability exert a stronger influence on their breeding success. Females that acquire dominant status also develop a suite of morphological, physiological and behavioural characteristics that help them to control other group members. Our results show that sex differences in parental investment are not the only mechanism capable of generating sex differences in reproductive competition and emphasize the extent to which competition for breeding opportunities between females can affect the evolution of sex differences and the operation of sexual selection.

Complex evolution of X and Y autosomal translocations in the giant mole-rat, Cryptomys mechowi (Bathyergidae)

Cross-species chromosome painting was used to determine homologous chromosomal regions between two species of mole-rat, the naked mole-rat, Heterocephalus glaber (2n = 60), and the giant mole-rat, Cryptomys mechowi (2n = 40), using flow-sorted painting probes representative of all but two of the H. glaber chromosomal complement. In total 43 homologous regions were identified in the C. mechowi genome. Eight H. glaber chromosomes are retained in toto in C. mechowi, and 13 produce two or more signals in this species. The most striking difference in the karyotypes of the two taxa concerns their sex chromosomes. The H. glaber painting probes identified a complex series of translocations that involved the fractionation of four autosomes and the subsequent translocation of segments to the sex chromosomes and to autosomal partners in the C. mechowi genome. An intercalary heterochromatic block (IHB) was detected in sex chromosomes of C. mechowi at the boundary with the translocated autosomal segment. We discuss the likely sequence of evolutionary events that has led to the contemporary composition of the C. mechowi sex chromosomes, and consider these in the light of prevailing views on the genesis of sex chromosomes in mammals.

Light-induced Fos expression in the suprachiasmatic nucleus of the four-striped field mouse, Rhabdomys pumilio: A southern African diurnal rodent

Previous studies have suggested that nocturnal and diurnal species of rodents differ in their circadian responses to light including phase shifts and early gene expression. Rhabdomys pumilio, the four-striped field mouse, is diurnal both in nature and in the laboratory. We studied in this species the response of the suprachiasmatic nucleus (SCN) to light stimuli at different time periods using light-induced expression of Fos as marker of neuronal activity. Fos induction in the SCN was investigated using immunohistochemistry and quantitative image analysis. The animals were exposed to a 15 min light pulse with monochromatic green light at different circadian times throughout a 24-h cycle. Animals maintained in constant darkness served as controls. R. pumilio exhibited an endogenous Fos rhythm in the SCN during constant darkness with highest expression during the subjective day at circadian time (CT) 2 and CT10. Photic stimulation resulted in significant Fos induction in the SCN at CT6, CT14, CT18 and CT22, compared to controls kept in constant darkness, with a peak of expression at CT22, i.e. during late subjective night, mainly due to expression in the ventral SCN. In tract tracing experiments based on the use of cholera toxin subunit B, we found that retinal fibres innervate mainly the contralateral ventral SCN. The intergeniculate leaflet received bilateral retinal innervation with overlap between ipsilateral and contralateral fibres. Altogether the data show that the rodent R. pumilio is a unique diurnal model for chronobiological studies.

Energetics reveals physiologically distinct castes in a eusocial mammal

Eusociality, which occurs among mammals only in two species of African mole-rat, is characterized by division of labour between morphologically distinct 'castes'. In Damaraland mole-rats (Cryptomys damarensis), colony labour is divided between 'infrequent worker' and 'frequent worker' castes. Frequent workers are active year-round and together perform more than 95% of the total work of the colony, whereas infrequent workers typically perform less than 5% of the total work. Anecdotal evidence suggests that infrequent workers may act as dispersers, with dispersal being limited to comparatively rare periods when the soil is softened by moisture. Here we show that infrequent workers and queens increase their daily energy expenditure after rainfall whereas frequent workers do not. Infrequent workers are also fatter than frequent workers. We suggest that infrequent workers constitute a physiologically distinct dispersing caste, the members of which, instead of contributing to the work of the colony and helping the queen to reproduce, build up their own body reserves in preparation for dispersal and reproduction when environmental conditions are suitable.

The energy costs of sexual dimorphism in mole-rats are morphological not behavioural

Different reproductive strategies of males and females may lead to the evolution of differences in their energetic costs of reproduction, overall energetic requirements and physiological performances. Sexual dimorphism is often associated with costly behaviours (e.g. large males might have a competitive advantage in fighting, which is energetically expensive). However, few studies of mammals have directly compared the energy costs of reproductive activities between sexes. We compared the daily energy expenditure (DEE) and resting metabolic rate (RMR) of males and females of two species of mole-rat, Bathyergus janetta and Georychus capensis (the former is sexually dimorphic in body size and the latter is not) during a period of intense digging when males seek females. We hypothesized that large body size might be indicative of greater digging or fighting capabilities, and hence greater mass-independent DEE values in males of the sexually dimorphic species. In contrast to this prediction, although absolute values of DEE were greater in B. janetta males, mass-independent values were not. No differences were apparent between sexes in G. capensis. By comparison, although RMR values were greater in B. janetta than G. capensis, no differences were apparent between the sexes for either species. The energy cost of dimorphism is most likely to be the cost of maintenance of a large body size, and not the cost of behaviours performed when an individual is large.

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.

Fos expression in the suprachiasmatic nucleus in response to light stimulation in a solitary and social species of African mole-rat (family Bathyergidae)

Mole-rats are strictly subterranean rodents that are rarely exposed to environmental light. They are well adapted to their environment and have reduced eyes and a severely regressed visual system. It has been shown, however, that mole-rats do exhibit endogenous circadian rhythms that can be entrained, suggesting an intact and functional circadian system. To determine whether light is the entraining agent in these animals, Fos expression in response to light pulses at different circadian times was investigated to obtain phase response curves. Light is integrated effectively in the suprachiasmatic nucleus of the Cape mole-rat (Georychus capensis), and Fos expression is gated according to the phase of the circadian clock. The Fos response in the Cape mole-rat was comparable to that of aboveground rodents. In contrast, the highveld mole-rat (Cryptomys hottentotus pretoriae) was less sensitive to light and did not show a selective Fos response according to the phase of the circadian cycle. Social species appear to be less sensitive to light than their solitary counterparts, which compares well with results from locomotor activity studies.

Characterization of gonadotrophin-releasing hormone precursor cDNA in the Old World mole-rat Cryptomys hottentotus pretoriae: high degree of identity with the New World guinea pig sequence

Regulation of pituitary gonadotrophins by the decapeptide gonadotrophin-releasing hormone 1 (GnRH1) is crucial for the development and maintenance of reproductive functions. A common amino acid sequence for this decapeptide, designated as 'mammalian' GnRH, has been identified in all mammals thus far investigated with the exception of the guinea pig, in which there are two amino acid substitutions. Among hystricognath rodents, the members of the family Bathyergidae regulate reproduction in response to diverse cues. Thus, highveld mole-rats (Cryptomys hottentotus pretoriae) are social bathyergids in which breeding is restricted to a particular season in the dominant female, but continuously suppressed in subordinate colony members. Elucidation of reproductive control in these animals will be facilitated by characterization of their GnRH1 gene. A partial sequence of GnRH1 precursor cDNA was isolated and characterized. Comparative analysis revealed the highest degree of identity (86%) to guinea pig GnRH1 precursor mRNA. Nevertheless, the deduced amino acid sequence of the mole-rat decapeptide is identical to the 'mammalian' sequence rather than that of guinea pigs. Successful detection of GnRH1-synthesizing neurones using either a guinea pig GnRH1 riboprobe or an antibody against the 'mammalian' decapeptide is consistent with the guinea pig-like sequence for the precursor and the classic 'mammalian' form for the decapeptide. The high degree of identity in the GnRH1 precursor sequence between this Old World mole-rat and the New World guinea pig is consistent with the theory that caviomorphs and phiomorphs originated from a common ancestral line in the Palaeocene to mid Eocene, some 63-45 million years ago.

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 endogenous rhythm of plasma melatonin and its regulation by light in the highveld mole-rat (Cryptomys hottentotus pretoriae): a microphthalmic, seasonally breeding rodent

The day- and night-time levels of plasma melatonin were measured in adult male and female highveld mole-rats, Cryptomys hottentotus pretoriae. This study aimed to assess whether melatonin secretion in this nocturnal, strictly subterranean but seasonally breeding rodent has a day-night rhythm and whether that rhythm is circadian and can be modified by photoperiod. In experiment 1, a day-night rhythm of plasma melatonin was found in all animals housed on a 12L:12D schedule, with significantly higher concentrations in the dark (D) compared with the light (L) phase. The increment of plasma melatonin concentration at night was the same on days 1 and 2 for animals in the control group and animals transferred to constant dark. The animals transferred to constant light substantially reduced the amplitude of the melatonin rhythm on day 2. This suggests that the endogenous melatonin rhythm in C. h. pretoriae has a circadian pattern, which can be synchronized by photoperiod and inhibited by exposure to light at night. In experiment 2, the concentration of plasma melatonin in animals kept under 14L:10D (long day, LD) conditions differed significantly from animals on 10L:14D (short day, SD). This finding supports the notion that C. h. pretoriae is sensitive to changes in day length.

The chronobiology of the Natal mole-rat, Cryptomys hottentotus natalensis

The Natal mole-rat, Cryptomys hottentotus natalensis, rarely, if ever, is exposed to external light cues because it occurs in completely sealed tunnel systems. As a result, their classical visual system is regressed, and therefore, their circadian system is expected proportionally to be expanded. Locomotor activity was investigated under a number of different photic regimes. Nine of the 12 mole-rats exhibited endogenous circadian rhythms of locomotor activity under constant darkness, with a mean free run period of 24.13 h (range 23.93-24.13 h), with these animals entrained to a light-dark cycle (12 L:12 D). Because C. hottentotus natalensis are able to entrain their locomotor activity to an external light source, light must reach the suprachiasmatic nucleus (SCN), suggesting a functional circadian clock. A clear day-night rhythm of melatonin secretion in animals housed under a neutral photoperiod (12 L:12 D) was observed, with higher melatonin concentrations in the dark compared with the light phase. The rhythm was maintained after the animals were transferred to either continuous light (LL) or dark (DD), suggesting that the endogenous rhythm was maintained under acute exposure to light and dark. However, under DD, the rhythm appeared to shift slightly, potentially as a result of the rhythm free running. These results show that C. hottentotus natalensis has endogenous rhythms of both locomotor activity and melatonin secretion, which are modulated by light.

A neuroanatomical and neuroendocrinological study into the relationship between social status and the GnRH system in cooperatively breeding female Damaraland mole-rats, Cryptomys damarensis

The gonadotrophin-releasing hormone (GnRH) system in female Damaraland mole-rats, Cryptomys damarensis, has been investigated to map the distribution of GnRH-immunoreactive (GnRH-IR) structures in the brain of this species and to assess whether changes in this system may mediate the inhibitory effect of social cues on fertility. The distribution of GnRH-IR cell bodies and fibres was similar to that of other mammals, forming a loose continuum along a septo-preoptico-infundibular pathway. GnRH-IR cell bodies were more abundant in the vicinity of the organum vasculosum of the lamina terminalis than in the medial basal hypothalamus. GnRH-IR cells and fibres were also found in the subfornical organ. The cell bodies were typically unipolar or bipolar. No differences were found in the morphology or size of the cell bodies or in the number of cells between non-reproductive females and reproductive females living together in a colony. However, GnRH concentrations, measured in the brain by radioimmunoassay, were significantly higher in non-reproductive females than in reproductive females; this finding was complemented by the reduced immunoreactivity for GnRH in the median eminence and proximal pituitary stalk of reproductive females. In contrast, the concentrations of GnRH measured by radioimmunoassay in non-reproductive and reproductive males did not differ. These results are consistent with the hypothesis that GnRH release is inhibited in the non-reproductive females but not in the non-reproductive males of this species.

Molecular insight into patterns of colony composition and paternity in the common mole-rat Cryptomys hottentotus hottentotus

We report the discovery of intraspecific variation in both colony composition and patterns of paternity in two populations of the social common mole-rat Cryptomys hottentotus hottentotus. These two populations represent the mesic and arid habitat extremes of the species' broad ecological range in South Africa. Until recently colonies of the common mole-rat were thought to consist of familial groups whereby all colony members were the offspring of a monogamous reproductive pair. The remaining colony members were thought to forego reproduction until both social and ecological conditions favoured dispersal and opportunities for independent outbreeding. Results from genetic assignment tests using microsatellite markers indicate that while colony composition is dominated by familial groups, colonies within both populations included both adult and subadult foreign conspecifics. Analysis of parentage reveals that the social organization of C. h. hottentotus is not that of strict monogamy; paternity of offspring was not assigned consistently to the largest, most dominant male within the colony. Moreover, a number of significantly smaller males were found to sire offspring, suggesting a sneak-mating strategy by subordinate within-colony males. Extra-colony extra-pair paternity (ECP) was also found to characterize C. h. hottentotus colonies, occurring with similar frequencies in both habitats. Both dominant established breeding males and subordinate males were identified as siring young in nonsource colonies. Furthermore, established breeding males were found to sire extra-colony young in the same season as siring young within their source colonies. We discuss the significance of these results within the context of the divergent ecological regimes characterizing the two sites and observe that our results revisit the accuracy of using behavioural and morphological characters, which have structured the basis of our understanding of the behavioural ecology of this species, as indicators of breeding status in mark-recapture studies.

Phylogeographical patterns of genetic divergence and speciation in African mole-rats (Family: Bathyergidae)

African mole-rats are subterranean Hystricomorph rodents, distributed widely throughout sub-Saharan Africa, and displaying a range of social and reproductive strategies from solitary dwelling to the 'insect-like' sociality of the naked mole-rat, Heterocephalus glaber. Both molecular systematic studies of Rodentia and the fossil record of bathyergids indicate an ancient origin for the family. This study uses an extensive molecular phylogeny and mitochondrial cytochrome b and 12s rRNA molecular clocks to examine in detail the divergence times, and patterns of speciation of the five extant genera in the context of rift valley formation in Africa. Based on a value of 40-48 million years ago (Myr) for the basal divergence of the family (Heterocephalus), we estimate divergence times of 32-40 Myr for Heliophobius, 20-26 Myr for Georychus/Bathyergus and 12-17 Myr for Cryptomys, the most speciose genus. While early divergences may have been independent of rifting, patterns of distribution of later lineages may have been influenced directly by physical barriers imposed by the formation of the Kenya and Western Rift, and indirectly by accompanying climatic and vegetative changes. Rates of chromosomal evolution and speciation appear to vary markedly within the family. In particular, the genus Cryptomys appears to have undergone an extensive radiation and shows the widest geographical distribution. Of the two distinct clades within this genus, one exhibits considerable karyotypic variation while the other does not, despite comparatively high levels of sequence divergence between some taxa. These different patterns of speciation observed both within the family and within the genus Cryptomys may have been a result of environmental changes associated with rifting.

Seasonal reproduction in the highveld mole-rat, Cryptomys hottentotus pretoriae (Rodentia: Bathyergidae)

The highveld mole-rat, Cryptomys hottentotus pretoriae, is a cooperatively breeding rodent that exhibits seasonal breeding and a reproductive division of labour. Body mass, reproductive-tract morphometrics, ovarian histology, and plasma oestrogen and progesterone concentrations were studied for both reproductive and non-reproductive females from 55 colonies, the main objective being to determine the inclination of this species towards seasonal breeding. Offspring are born from July through to November. However, qualitative analysis of ovarian histology revealed that reproductive females retain the potential for ovulation and subsequent production of corpora lutea during the late-summer nonbreeding period (December–March). Seasonal differences were found in ovarian morphometrics and hormone concentrations that are associated with enhanced follicular activation in April and May and subsequent conceptions from July through to November during the breeding period. The nonbreeding period coincides with maximal dispersal opportunities in the summer-rainfall areas inhabited by the highveld mole-rat. Body mass, reproductive-tract morphometrics, testicular histology, and plasma testosterone concentrations were determined for reproductive and non-reproductive males from 37 colonies. Available evidence suggests that there is a gradual increase in testicular mass for reproductive males as the breeding season approaches, but after September the testicular parameters fall. Seminiferous-tubule diameter was significantly greater in reproductive males but exhibited no seasonal variation. Testosterone concentrations were higher in reproductive males. Current data support a lack of gonadal regression in males during the nonbreeding season.

Simple roost nests confer large energetic savings for sparrow-weavers

White-browed sparrow-weavers (Plocepasser mahali, body mass 40 g) are group-living passerines adapted to the semi-arid environment of north-eastern and south-western Africa. During winter, the nocturnal ambient temperature of these regions often falls below 0 degrees C. imposing conditions demanding an increase in thermoregulatory heat production. Individuals roost throughout the year in inverted U-shaped roost nests. We investigated the energetic advantages of roosting by measuring nest and ambient temperatures in the field, as well as the resting metabolic rate (RMR) of the birds. The sparrow-weavers exhibited a wide thermoneutral zone (13 degrees C - 32 degrees C). Although RMR at thermoneutrality (40.2 J g.h(-1)) conforms with those of other passerines. the value at 0 degrees C (74.8 J g.h(-1)) is significantly lower than expected. The slope of the line below the lower critical temperature is unexpectedly steep, however, and appears to cause the physiological requirement for nest roosting due to a high cost of thermoregulation at low temperatures, perhaps due to shivering or non-shivering thermogenesis. The nest temperature at 0 degrees C ambient is 5 degrees C. resulting in a saving of some 7% in the energy spent during winter nights when food resources are in short supply compared with the rest of the year.

Reproductive suppression in female Damaraland mole-rats Cryptomys damarensis: dominant control or self-restraint?

Colonies of Damaraland mole-rats Cryptomys damarensis exhibit a high reproductive skew. Typically one female breeds and the others are anovulatory. Two models, the dominant control model (DCM) and the self-restraint model (SRM), have been proposed to account for this reproductive suppression. The DCM proposes that suppression is under the control of the dominant breeder and is imposed by mechanisms such as aggression, pheromones and interference with copulation, whereas the SRM does not involve aggression directed towards non-breeders and may function in order to minimize inbreeding. We investigated potential proximate mechanisms involved in the suppression of females in a series of experiments. Socially induced stress through aggression did not appear to be responsible for anovulation. Nor did breeders actively interfere with subordinate copulation. Females were physiologically suppressed when housed in intact colonies. However, as predicted by the DCM, they did not become reproductively active when removed from the presence of breeders. We found no evidence that pheromonal cues block ovulation. We suggest that the SRM is the basic model found in the Damaraland mole-rat and that self-restraint functions in order to minimize inbreeding by restricting reproduction until an unrelated male is present. This would explain the rapid onset of reproductive activation in females when paired with an unrelated male, as demonstrated in this study.

Anovulation in non-reproductive female Damaraland mole-rats (Cryptomys damarensis)

Within colonies of Damaraland mole-rats (Cryptomys damarensis), anovulation in non-reproductive females is thought to play an important role in maintaining reproductive skew. Pituitary sensitivity and ovarian structure were examined in three groups of females that differed with respect to their social environment and breeding status to determine whether anovulation is due to inhibitory social cues or is merely the result of a lack of copulatory stimulation. The contribution of gonadal steroid negative feedback to neuroendocrine differences in the reproductive systems of the respective groups was also investigated. LH secretion after a 0.5 micrograms GnRH challenge in females that had been removed from the presence of the breeding individuals for at least 6 months (removed non-reproductive females) was significantly higher than in non-reproductive females in the colony, but significantly lower than in reproductive females. In both removed non-reproductive females and reproductive females, corpora lutea were observed in ovaries of seven of eight females, indicating that ovulation occurs spontaneously in subordinate females on removal from the breeding pair. Circulating progesterone concentrations in removed non-reproductive females were significantly higher than in non-reproductive females, indicating that circulating progesterone is not responsible for infertility in non-reproductive females. Indeed, after hystero-ovariectomy, reproductive females continued to show significantly greater GnRH-stimulated LH secretion than non-reproductive females. Thus, differential inhibition of gonadotrophin secretion in breeding and non-breeding females occurs independently of gonadal steroids. It is concluded that female Damaraland mole-rats are spontaneous ovulators and that anovulation results from inhibitory social cues within the colony, not a lack of copulatory stimulation. Since non-reproductive females are infertile, inhibition of the hypothalamo-pituitary-gonadal axis has the potential to play a causal role in maintaining reproductive skew in colonies of C. damarensis.

Anovulation in non-reproductive female Damaraland mole-rats (Cryptomys damarensis)

Within colonies of Damaraland mole-rats (Cryptomys damarensis), anovulation in non-reproductive females is thought to play an important role in maintaining reproductive skew. Pituitary sensitivity and ovarian structure were examined in three groups of females that differed with respect to their social environment and breeding status to determine whether anovulation is due to inhibitory social cues or is merely the result of a lack of copulatory stimulation. The contribution of gonadal steroid negative feedback to neuroendocrine differences in the reproductive systems of the respective groups was also investigated. LH secretion after a 0.5 micrograms GnRH challenge in females that had been removed from the presence of the breeding individuals for at least 6 months (removed non-reproductive females) was significantly higher than in non-reproductive females in the colony, but significantly lower than in reproductive females. In both removed non-reproductive females and reproductive females, corpora lutea were observed in ovaries of seven of eight females, indicating that ovulation occurs spontaneously in subordinate females on removal from the breeding pair. Circulating progesterone concentrations in removed non-reproductive females were significantly higher than in non-reproductive females, indicating that circulating progesterone is not responsible for infertility in non-reproductive females. Indeed, after hystero-ovariectomy, reproductive females continued to show significantly greater GnRH-stimulated LH secretion than non-reproductive females. Thus, differential inhibition of gonadotrophin secretion in breeding and non-breeding females occurs independently of gonadal steroids. It is concluded that female Damaraland mole-rats are spontaneous ovulators and that anovulation results from inhibitory social cues within the colony, not a lack of copulatory stimulation. Since non-reproductive females are infertile, inhibition of the hypothalamo-pituitary-gonadal axis has the potential to play a causal role in maintaining reproductive skew in colonies of C. damarensis.

Circulating LH levels and the response to exogenous GnRH in the common mole-rat: implications for reproductive regulation in this social, seasonal breeding species

The effects of breeding season and reproductive status on male and female reproduction were investigated in the common mole-rat, Cryptomys hottentotus hottentotus, a cooperatively breeding rodent which exhibits a unique combination of seasonal breeding and a reproductive division of labor. Pituitary function was examined by measuring the luteinizing hormone (LH) responses to single doses of 2 microg exogenous gonadotrophin-releasing hormone (GnRH) and physiological saline in 69 males and 58 females from 35 wild caught colonies. Neither males nor females exhibited any apparent manifestation of season on basal LH concentrations or on pituitary sensitivity to stimulation by exogenous GnRH. The continuance of reproductive function during the nonbreeding period is essential in common mole-rat males and females, as this period coincides with the period of maximal dispersal opportunity in the winter rainfall area they inhabit. Normal circulating levels of reproductive hormones in dispersing animals may aid intersexual recognition, assist pairbond formation, and thus prime animals for independent reproduction. Circulating basal concentrations of LH as well as LH levels measured in response to a single exogenous GnRH challenge were not significantly different between the reproductive and non-reproductive groups of either sex, suggest the absence of a physiologically well-defined suppression of reproduction in subordinate common mole-rats.

Inbreeding avoidance and reproductive skew in a cooperative mammal

In animal social groups, socially subordinate individuals frequently show low reproductive success or completely fail to breed. This suppression of subordinate reproduction is currently typically attributed to control by dominant individuals. However, subordinates in cooperative groups often lack access to unrelated mates, and an alternative possibility is that their reproduction is limited by inbreeding avoidance. Using the eusocial Damaraland mole-rat Cryptomys damarensis, this paper provides the first experimental evidence, to our knowledge, for this explanation. Subordinate, non-breeding female mole-rats were given access to unrelated mates while remaining in the presence of dominant females, and many became reproductively active soon after unrelated males were introduced. Inbreeding avoidance and the availability of unrelated mates provides a plausible and untested explanation for variation in reproductive skew across animal societies.