Masticatory musculature of the African mole-rats (Rodentia: Bathyergidae)

The Bathyergidae, commonly known as blesmols or African mole-rats, is a family of rodents well-known for their subterranean lifestyle and tunnelling behaviour. Four of the five extant bathyergid genera (Cryptomys, Fukomys, Georychus and Heliophobius) are chisel-tooth diggers, that is they dig through soil with their enlarged incisors, whereas the remaining genus (Bathyergus) is a scratch-digger, only using its forelimbs for burrowing. Heterocephalus glaber, the naked mole-rat, is also a chisel-tooth digger and was until recently included within the Bathyergidae (as the most basally branching genus), but has now been placed by some researchers into its own family, the Heterocephalidae. Given the importance of the masticatory apparatus in habitat construction in this group, knowledge and understanding of the morphology and arrangement of the jaw-closing muscles in Bathyergidae is vital for future functional analyses. Here, we use diffusible iodine-based contrast-enhanced microCT to reveal and describe the muscles of mastication in representative specimens of each genus of bathyergid mole-rat and to compare them to the previously described musculature of the naked mole-rat. In all bathyergids, as in all rodents, the masseter muscle is the most dominant component of the masticatory musculature. However, the temporalis is also a relatively large muscle, a condition normally associated with sciuromorphous rodents. Unlike their hystricomorphous relatives, the bathyergids do not show an extension of the masseter through the infraorbital foramen on to the rostrum (other than a very slight protrusion in Cryptomys and Fukomys). Thus, morphologically, bathyergids are protrogomorphous, although this is thought to be secondarily derived rather than retained from ancestral rodents. Overall, the relative proportions of the jaw-closing muscles were found to be fairly consistent between genera except in Bathyergus, which was found to have an enlarged superficial masseter and relatively smaller pterygoid muscles. It is concluded that these differences may be a reflection of the behaviour of Bathyergus which, uniquely in the family, does not use its incisors for digging

Energetic Benefits of Sociality Offset the Costs of Parasitism in a Cooperative Mammal

We thank the owners for access to their property for animal capture and KwaZulu-Natal Nature Conservation Service for issuing the capture permit. This research was funded by the NRF-SAR Chair for Mammalian Behavioural Ecology and Physiology to NCB and University of Pretoria PDRF's to MS and HL. Many assistants were involved with fieldwork but we would especially like to thank Marietjie Oosthuizen and Craig Jackson for their help. This research was funded by the Department of Science and Technology/National Research Foundation-South African Research Chairs Initiative Chair for Mammalian Behavioural Ecology and Physiology to N.C.B. and University of Pretoria Postdoctoral Research Fellowships to M.S. and H.L. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Possible modulatory effects of male cues and social system on luteinizing hormone and pituitary sensitivity in two African mole-rats

The current study set out to investigate the potential effects of olfactory stimuli on the basal circulating levels of luteinizing hormone (LH) and the response of the pituitary to an exogenous gonadotropin-releasing hormone (GnRH) challenge in two mole-rat species with induced ovulation but contrasting mating and social systems. Females were either kept in isolation, allowed only olfactory and auditory contact or in physical contact with a male. Basal LH as well as pituitary challenged LH blood samples were collected after six hours. Post-challenge LH levels were significantly elevated compared to baseline levels in both species. However, neither basal nor post-challenge LH levels differed significantly between treatments for females of either species. At the same time, while baseline LH was comparable between the two species, post-challenge levels were significantly greater for the solitary species. Our findings negate a modulatory role of male cues on LH levels but suggest increases in pituitary sensitivity in the solitary species. This could enhance reproductive success in species with only sporadic encounters between the sexes and merits further studies in other species.The National Research Foundation. N.C.B. acknowledges funding for a DST-NRF SARChI Chair of Mammalian Behavioural Ecology and Physiology. H.L. acknowledges a postdoctoral research fellowship from the University of Pretoria.http://www.bioone.org/loi/afzoab201

Determinants of helminth infection in a subterranean rodent, the Cape dune mole-rat (Bathyergus suillus)

The helminth fauna of the largest bathyergid, the Cape molerat (Bathyergus suillus) was studied throughout an entire calendar year. The species richness encountered was low, with only 3 species of nematodes (Longistriata bathyergi, Mammalakis macrospiculum, and Trichostrongylus sp.) and 2 species of cestodes (Taenia sp. and Rodentolepis sp.). At less than 10%, the prevalence for all helminths species was similarly low and may be a result of the solitary lifestyle and the subterranean habitat exploited by this rodent. Clear seasonal patterns were apparent for the most common nematode (L. bathyergi), and prevalence and abundance were highest among non-pregnant females compared to males and pregnant females. Dispersal patterns associated with the mating system of the host could explain this pattern. In contrast, the prevalence of the most common cestode (Taenia sp.) was neither determined by season nor host sex, suggesting that foraging habits may constantly expose B. suillus to this parasite.http://asp.unl.edu/index.php?option=com_content&view=article&id=39&Itemid=48ab201

Gnrh mRNA expression in the brain of cooperatively breeding female Damaraland mole-rats

The Damaraland mole-rat (Fukomys damarensis) is a eusocial, subterranean rodent, in which breeding is limited to a single reproductive pair within each colony. Non-reproductive females, while in the confines of the colony, exhibit socially-induced infertility. Anovulation is thought to be caused by a disruption in the normal gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus. In order to assess whether social suppression is associated with altered GnRH mRNA expression in the brain we investigated the distribution and gene expression levels by means of in situ hybridization in female breeders and nonbreeders from field captured colonies of the Damaraland mole-rat. We found expression of GnRH mRNA as a loose network in several forebrain areas of female Damaraland mole-rats with the majority of labelling in the preoptic and anterior hypothalamus. The distribution matched previous findings using immunocytochemistry in this and other social mole-rat species. Quantification of the hybridisation signal revealed no difference between breeding and non-breeding females in the average optical density of the hybridization signal and the size of the total area covered by GnRH mRNA. However, analysis along the rostro-caudal axis revealed significantly elevated GnRH mRNA expression in the rostral preoptic region of breeders compared to non-breeders, while the latter had increased GnRH mRNA expression at the caudal level of the anterior hypothalamus. This study indicates that social suppression affects the expression of GnRH mRNA in female Damaraland mole-rats. Furthermore, differential regulation occurs within different neuron subpopulations.This work was supported by a fellowship from the University of Pretoria to CV. We are grateful to the DST-NRF for funding to NB.http://www.reproduction-online.org2018-04-30hb2017Zoology and Entomolog

The importance of the aggregation of ticks on small mammal hosts for the establishment and persistence of tick-borne pathogens : an investigation using the R0 model

Aggregation of parasites amongst hosts is important for the epidemiology of vector-borne diseases because hosts that support the majority of the vector population are responsible for the majority of pathogen transmission. Ixodes ricinus ticks transmit numerous pathogens of medical importance including Borrelia burgdorferi s.l. and tick-borne encephalitis virus. One transmission route involved is ‘co-feeding transmission’, where larvae become infected via feeding alongside infected nymphs. The aggregation of ticks on hosts leads to an increase in the number of larvae feeding alongside nymphs, increasing the transmission potential via this route. The basic reproduction number, R0, can be used to identify whether a pathogen will become established if introduced. In the current study we use previously published tick, and pathogen, specific data to parameterize an R0 model to investigate how the degree of aggregation of ticks on hosts affects pathogen persistence. The coincident aggregated distribution permitted the establishment of tick-borne encephalitis virus but did not influence whether B. burgdorferi s.l. became established. The relationship between the k-exponent of the negative binomial distribution and R0 was also defined. Therefore, the degree of aggregation of ticks on small mammal hosts has important implications for the risk to human health in a given area.A University of Pretoria Postdoctoral Fellowship awarded to A. Harrison and the DSTNRF South African Research Chair of Behavioural Ecology and Physiology awarded to N.C. Bennett.http://journals.cambridge.org/action/displayJournal?jid=parab201

Reproductive status-dependent dynorphin and neurokinin B gene expression in female Damaraland mole-rats

Damaraland mole rats (Fukomys damarensis) are cooperatively breeding, subterranean mammals, which exhibit high reproductive skew. Reproduction is monopolized by the dominant female of the group, while subordinates are physiologically suppressed. The blockade of reproduction results from an inhibition of ovulation, which is caused by inadequate secretion of luteinizing hormone (LH) from the pituitary, which in turn might be brought about by a disruption of the normal GnRH secretion from the hypothalamus. The neuropeptides dynorphin and neurokinin B are expressed together with kisspeptin in a subpopulation of neurons in the arcuate nucleus (ARC). This neuron population is termed KNDy neurons and is considered to constitute the GnRH pulse generator. To assess whether dynorphin (encoded by the Pdyn gene) and neurokinin B (NKB, encoded by the Tac3 gene) are involved in the mechanism of reproductive suppression we investigated the distribution and gene expression of Pdyn and Tac3 by means of in situ hybridisation in wild-caught female Damaraland mole-rats with different reproductive status. In both reproductive phenotypes, substantial Pdyn expression was found in several brain regions of the telencephalon including the cerebral cortex, the striatum, the hippocampus, the amygdala and the olfactory tubercle. Within the hypothalamus Pdyn expression occurred in the paraventricular nucleus, the dorsomedial nucleus, the supraoptic nucleus, the ventromedial nucleus and the ARC. Prominent Tac3 expression was found in the habenula, the bed nucleus of the stria terminalis, the cerebral cortex, the striatum, the hippocampus, the amygdala, the dorsomedial nucleus, the ARC and the lateral mammillary nucleus. Quantification of the gene expression levels in the ARC revealed decreased Pdyn and increased Tac3 expression in breeding compared to nonbreeding females. This suggests that both neuropeptides play a role in the regulation of reproduction in Damaraland mole-rats. Their exact role in mediating the inhibition of GnRH release in nonbreeding females remains to be determined.The University of Pretoria to CV and funding from the DST-NRF to NB.http://www.elsevier.com/locate/jchemneu2020-12-01hj2020Zoology and Entomolog

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.A fellowship from the University of Pretoria to CV and the DST-NRF for funding to NB.http://wileyonlinelibrary.com/journal/jne2019-03-18hj2018Zoology and Entomolog

Mole rats act as ecosystem engineers within a biodiversity hotspot, the Cape Fynbos

Through their burrowing and foraging activities, subterranean rodents disturb large amounts of soil. As a result, they may modify physical and chemical soil properties and thus change the productivity, structure and dynamics of plant communities. To date, research on the ecological importance of fossorial mammals has focussed predominantly on subterranean rodents in North and South America, Europe and Asia. Surprisingly, despite the potential of them filling a similar ecological niche, very few studies have focussed on the impacts of mole-rats (Bathyergidae) in Africa. To determine how mole-rats modulate their environment, we examined the soil and vegetation properties of mole-rat-modified habitats in the Cape Floristic Region, South Africa. We predicted that excavation would result in mound soils having higher nutrient levels, more uniform soil particle profiles and lower compactness compared to undisturbed soils. Furthermore, we expected their digging and foraging activities would change plant species composition and increase plant productivity and diversity. As predicted, we found that soils disturbed by mole-rats had higher nutrient levels and lower compactness compared to undisturbed soils, and an altered plant species composition. However, in contrast to our predictions, mounds had a finer particle size profile, and mole-rat burrowing and foraging lowered the overall aboveground plant biomass. Most importantly, the presence of mole-rats enhanced plant species richness. However, as disturbance increased plant species richness declined. Our findings suggest that in Africa, mole-rats fulfil the same ecological niche as their ecological cognates in other ecosystems and thus ultimately act as ecosystem engineers.The study was funded through a University of Pretoria post-doctoral fellowship (to NH) and a DST-NRF SARChI Chair of mammal behavioural ecology and physiology (to NCB).http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-7998hb2013ab201

Partitioning of Evaporative Water Loss into Respiratory and Cutaneous Pathways in Wahlberg's Epauletted Fruit Bats ( Epomophorus wahlbergi

Please read abstract in the article.National Research Foundation.http://www.journals.uchicago.edutoc/pbz/currenthb201