Stress in an underground empire

The naked mole-rat (Heterocephalus glaber) and the Damaraland mole-rat (Fukomys damarensis) live in large colonies in underground tunnel systems in sub-Saharan Africa. Most members of the colonies are suppressed from reproduction and they are unlikely to reproduce during their lifetime. Only one female and a small number of males reproduce. This extreme cooperative social system has fascinated researchers since the naked mole-rat was first described as eusocial. Despite much research into the mechanisms of social suppression, the exact mechanisms are still unclear. Much evidence points towards high glucocorticoid concentrations caused by agonistic behaviour by the breeding female suppressing reproduction of non-breeders, but laboratory studies have not found any differences in glucocorticoids between breeders and non-breeders. There is, however, considerable evidence from field studies and other social mole-rats that social stress may indeed be an important factor of social suppression in social mole-rats and that those mechanisms are affected by the stability of the colony and environmental conditions. This review aims to provide a summary of the current knowledge of the relationship between environmental conditions, colony stability, glucocorticoids and reproductive suppression in social mole-rat species and suggests some avenues for future research.https://royalsocietypublishing.org/journal/rsblam2023Mammal Research InstituteZoology and Entomolog

Endoparasites of the eastern rock sengi (Elephantulus myurus) from South Africa

The endoparasite fauna of the eastern rock sengi (Elephantulus myurus Thomas and Schwann) was studied for the first time for any sengi species from September 2007 until August 2008 in the Limpopo Province of South Africa. From the 121 sengis examined, we recovered 11 endoparasite taxa including 9 nematodes, 1 cestode family (Hymenolepididae) and 1 pentastomid species [Armillifer armillatus (Wyman, 1834)]. The overall endoparasites prevalence was high at 100% and largely attributable to the nematode Maupasina weissi Seurat, 1913, with only a single individual being parasite free. Despite the high diversity, species richness was low (1.58 ± 0.06) and only M. weissi and spiruroid larvae occurred at a prevalence exceeding 8%. The abundance of M. weissi varied significantly between seasons and was lowest in summer and autumn. In contrast, the abundance of spiruroid larvae remained relatively constant across seasons in males but was significantly higher in spring and summer compared to winter in females. These patterns may be generated by an accumulation of M. weissi with age as well as sex-specific seasonal shifts in diet. An updated list on the hosts and geographic range of parasites of sengis is provided.NRF and the University of Pretoria.http://digitalcommons.unl.edu/jrnlparasitologyhb201

Endoparasites of the spiny mouse (Acomys spinosissimus) from South Africa

The endoparasite fauna of the spiny mouse (Acomys spinosissimus) was studied for the first time from April 2007 until April 2009 in a population from the Limpopo Province of South Africa. In a total of 129 mice examined, only 6 endoparasite taxa were found, 2 nematode species (Syphacia minuta, Monanema joopi), 1 genus of cestodes (Rodentolepis spp.), and unidentified hymenolepidid fragments. In addition, 1 pentastomid species (Armillifer grandis) as well as unidentified porocephalid specimens were recovered. The overall prevalence was low, at 15.5%, and only 1 individual harbored more than 1 parasite species. With 12.4% prevalence, S. minuta was the most prevalent parasite. Its prevalence and abundance were significantly higher during the dry and cooler season than during the wet and warm season, while a female-biased burden was observed during the wet season only. For the remaining parasite species, low prevalence prevented meaningful statistical analyses. The observed parasite species richness, prevalence, and abundance for A. spinosissimus were low compared to values reported for other Acomys spp. This may be linked to the lack of anthropogenic influences in the study population as well as the small size of A. spinosissimus.http://www.journalofparasitology.org/loi/parahb201

Abiotic and biotic determinants of tick burdens in the eastern rock sengi (Elephantulus myurus)

Ticks are important vectors of pathogens of medical and veterinary importance worldwide. Despite their economic importance our current knowledge about the factors affecting tick prevalence and abundance in tropical and subtropical regions is rather limited. Both abiotic (e.g. temperature) as well as biotic variables (e.g. host sex) have been identified as key determinants of distributions. Eastern rock sengis or elephant shrews (Elephantulus myurus, Thomas & Schwann) are widely distributed throughout Africa and can harbour a large number of tick species and substantial tick burdens. In the current study we evaluated the contribution of climate and host factors on tick burdens of sengis. Throughout the year sengis carried high abundances of immature stages of a single tick species, Rhipicephalus sp. near warburtoni. There was no evidence that host parameters affected tick burdens. However, larval abundance decreased with increasing ambient temperatures and both larvae and nymphs were negatively affected by rainfall two months prior to the sampling month. In addition, nymphal burdens decreased with increasing minimum temperatures. Our results suggest that climate factors are the largest constraint for the immature stages of R. sp. near warburtoni and that eastern rock sengis could play a crucial role in the dynamics of tick-borne diseases due to the large tick burdens they can sustain.KM was supported by a doctoral grant from the NRF and HL by a Research Fellowship from the University of Pretoria. IGH acknowledges funding from the University of Pretoria and the NRF.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2915ab201

Effects of life-history traits on parasitism in a monogamous mammal, the eastern rock sengi (Elephantulus myurus)

The distribution of parasites is often characterised by substantial aggregation with a small proportion of hosts harbouring the majority of parasites. This pattern can be generated by abiotic and biotic factors that affect hosts and determine host exposure and susceptibility to parasites. Climate factors can change a host’s investment in life-history traits (e.g. growth, reproduction) generating temporal patterns of parasite aggregation. Similarly, host age may affect such investment. Furthermore, sex-biased parasitism is common among vertebrates and has been linked to sexual dimorphism in morphology, behaviour and physiology. Studies exploring sex-biased parasitism have been almost exclusively conducted on polygynous species where dimorphic traits are often correlated. We investigated the effects of season and life-history traits on tick loads of the monogamous eastern rock sengi (Elephantulus myurus). We found larger tick burdens during the non-breeding season possibly as a result of energetic constraints and/or climate effects on the tick. Reproductive investment resulted in increased larval abundance for females but not males and may be linked to sex-specific life-history strategies. The costs of reproduction could also explain the observed age effect with yearling individuals harbouring lower larval burdens than adults. Although adult males had the greatest larval tick loads, host sex appears to play a minor role in generating the observed parasite heterogeneities. Our study suggests that reproductive investment plays a major role for parasite patterns in the study species.National Research Foundation (NRF), HL a Research Fellowship from the University of Pretoria and IGH funding from the University of Pretoria.http://www.springerlink.com/content/0028-1042/nf201

The mode of ovulation in the Namaqua rock mouse, Micaelamys namaquensis

The pattern of ovulation in mammals is generally considered to be either spontaneous or induced by copulation, with environmental and social factors playing a key role in determining the specific mode of ovulation that would maximize the reproductive potential of the species. This study aims to determine whether the Namaqua rock mouse (Micaelamys namaquensis (A. Smith, 1834)) is a spontaneous or induced ovulator. Females were divided into three treatments differing in the degree of contact with a male. Namely, seven control females had no contact with a male; a further seven separated females had only chemical, auditory, and visual contact with a male; whereas six females had intermittent periods of full contact with a vasectomized male. Ovarian size, follicular development, and plasma progesterone concentrations were compared between the three treatments. Penile morphology was also investigated. Corpora lutea were found in all three treatments and the penis was smooth without any ridges or spikes, indicating that M. namaquensis is a spontaneous ovulator. Interestingly, however, the presence of a male (physical as well as just visual and olfactory) positively affected ovarian size, ovulation, and plasma progesterone concentrations. This signifies that although M. namaquensis ovulates spontaneously, male contact significantly influences ovulation rate and ultimately reproductive success.L’ovulation chez les mammifères est généralement considérée comme étant soit spontanée ou induite par la copulation, des facteurs ambiants et sociaux jouant un rôle clé dans la détermination du mode d’ovulation précis qui maximise le potentiel de reproduction d’espèces données. L’objectif de l’étude était de déterminer si l’ovulation chez la souris Micaelamys namaquensis (A. Smith, 1834) est spontanée ou induite. Des femelles ont été assujetties a` trois traitements qui différaient selon le degré de contact avec un mâle : sept femelles de référence n’ont pas été mises en contact avec un mâle, sept autres femelles n’ont eu que des contacts chimiques, auditifs et visuels avec un mâle, alors que six femelles ont été en contact direct, de manière intermittente, avec un mâle vasectomisé. La taille des ovaires, le développement folliculaire et les taux de progestérone plasmatique des trois groupes ont été comparés. La morphologie du pénis a également été examinée. La présence de corps jaunes a été notée chez les femelles des trois groupes et le pénis était lisse, sans crête ni pointe, ce qui indique une ovulation spontanée chez M. namaquensis. Il est toutefois intéressant de noter que la présence d’un mâle (physique ou seulement visuelle ou olfactive) a un effet positif sur la taille des ovaires, l’ovulation et les taux de progestérone plasmatique. Cela signifie que, bien que l’ovulation soit spontanée chez M. namaquensis, le contact avec un mâle a une influence significative sur le taux d’ovulation et, en bout de ligne, sur le succès de reproduction.The study was funded by a South African Research Chair for mammalian behavioural ecology and physiology awarded to N.C.Bennett by the National Research Foundation (NRF). K. Medger acknowledges funding from the University of Pretoria for postdoctoral research.http://www.nrcresearchpress.com/loi/cjzhb201

Seasonal reproduction in the eastern rock elephant-shrew : influenced by rainfall and ambient temperature?

Because environmental conditions vary seasonally in most regions, many small mammals reproduce at a specific time of the year to maximize their reproductive success. In the tropics and subtropics, the breeding season is usually determined by the extent of the dry and rainy seasons. We investigated the seasonality of reproduction in the eastern rock elephant-shrew (Elephantulus myurus), over a 12-month period and attempted to elucidate the factors that may influence seasonal reproduction in this endemic African mammal. E. myurus breeds seasonally during the warm and wet spring and summer months and cessation of breeding occurs during the cold and dry winter months of the southern hemisphere. Pregnant females were only collected from August through to January. Ovarian size and plasma progesterone started to increase a few months prior to the first rains, were highest in October and decreased thereafter. Follicular growth and corpora body numbers corresponded to this seasonal reproductive pattern. Testes and seminiferous tubule size and plasma testosterone concentration has already started to increase during the coldest months, 2 months prior to reproductive onset in females. We propose that seasonal reproduction evolved in E. myurus because of seasonally changing food availability brought about by severe seasonal changes in rainfall and ambient temperature. The direct effects of rainfall and ambient temperature on reproduction of E. myurus are ambiguous, and we discuss other environmental factors that may trigger reproductive onset in this species.A South African Research Chair of Mammalian Behavioural Ecology and Physiology awarded to N.C. Bennett by the National Research Foundation (NRF). K. Medger acknowledges a doctoral grant from the NRF.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-799

Monanema joopi n. sp. (Nematoda, Onchocercidae), parasite d’Acomys (Acomys) spinosissimus Peters, 1852 (Muridae) en Afrique du Sud, et commentaires sur ce genre de filaire

Monanema joopi n. sp. is described from blood drawn from the heart of the murid Acomys (Acomys) spinosissimus in South Africa. It is characterised by a non-bulbous cephalic extremity, shared with only one of its five congeners, and a cylindrical tail with caudal alae and a spicular ratio of 2.7 in the male. As is typical for the genus, microfilariae are skin-dwelling. They are 185 to 215 micrometres long and have no refractory granules beneath their sheath. A key to the species of Monanema is presented and an amended generic description, based on the six currently known species, is proposed. Species of Monanema are primarily lymphatic and the low intensity of infection with M. joopi n. sp. in blood from the heart, might suggest that not all adults settle in the heart cavities. One might also consider that other, more susceptible rodents serve as hosts for this parasite as well. To date, the geographic range of Monanema includes North America, Africa and Australia, each with representatives of a different lineage. Given the present hypotheses on the evolutionary origin and subsequent migrations of rodents, we expect the origin of Monanema to be in the Palearctic-Oriental region.Description de Monanema joopi n. sp., récolté dans le sang cardiaque d’Acomys (Acomys) spinosissimus en Afrique du Sud. L’espèce est caractérisée par une extrémité céphalique non bulbeuse, partagée avec un seul des cinq congénères, et chez le mâle, une queue cylindrique avec des ailes caudales et un rapport spiculaire de 2,7. Les microfilaires sont dermiques, ce qui est caractéristique du genre. Elles sont longues de 185-215 μm et n’ont pas de granules réfringents sous la gaine. Une clé des espèces de Monanema est présentée, ainsi qu’un amendement de la définition générique, basée sur les six espèces. Les espèces de Monanema sont fondamentalement lymphatiques et la faible infection par M. joopi n. sp. dans le sang cardiaque permet de suspecter d’autres localisations des adultes. Il se peut aussi que d‘autres rongeurs plus réceptifs soient parasités. Actuellement, la distribution géographique de Monanema comprend l’Amérique du Nord, l’Afrique et l’Australie, et chaque région a des représentants de différentes lignées. D’après les hypothèses actuelles sur l’origine et les migrations ultérieures des rongeurs, nous pensons que Monanema est originaire de la région palearctico-orientale.Junker was sponsored during a two-month’s visit as invited professor by the Muséum National d’Histoire Naturelle, Paris, France. K. Medger was supported by a doctoral grant from the NRF and H. Lutermann by a Research Fellowship from the University of Pretoria.http://www.parasite-journal.org/am2013ab201

Reproductive photoresponsiveness in male spiny mice from South Africa

Many seasonally breeding mammals use changes in photoperiod as a reliable cue to time reproduction. Photoperiodic timing assists an animal in predicting annual environmental changes in its habitat and therefore, enables it to accurately time reproductive events to the most favourable conditions. Changes in day length are more pronounced in the temperate regions and photoperiod is used as a cue for reproduction by most mammals above 30° latitude; however, a number of subtropical species also use this proximate factor to regulate their reproductive cycle. We investigated the reproductive photoresponsiveness of 14 male spiny mice (Acomys spinosissimus) from southern Africa to short-day (SD; 8 h light : 16 h dark) and long-day (LD; 16 h light : 8 h dark) photoperiods. Testicular mass and volume, seminiferous tubule diameter and plasma testosterone concentrations significantly increased in animals subjected to LD and they were regressed when the males were kept under SD. Body mass of the males was not significantly affected by the photoperiodic conditions. Although male A. spinosissimus appear to use photoperiod as a proximate factor to regulate reproduction seasonally, other environmental factors, such as rainfall, food quantity and quality as well as temperature, may regulate reproduction in A. spinosissimus in concert with photoperiod. In conclusion, the present study demonstrates the significance of photoperiodic time-measuring systems in the regulation of seasonal reproduction in a subtropical rodent.This research was funded by a South African Research Chair of Mammalian Behavioural Ecology and Physiology awarded to N.C. Bennett by the South African Department of Science and Technology (DST) and the South African National Research Foundation (NRF). K. Medger acknowledges a doctoral grant from the NRF.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-7998ab201

Is reproduction of male eastern rock sengis (Elephantulus myurus) from southern Africa affected by photoperiod?

Many mammals use the change in day-length to time physiological and behavioural activities on a seasonal basis. Particularly mammals from temperate regions use photoperiod to regulate reproductive functions; however, information on the role of photoperiod in small mammals from the tropics and sub-tropics is scarce. We studied the response of the reproductive system of male eastern rock sengis (Elephantulus myurus) from southern Africa to photoperiods of differing length. Elephantulus myurus breeds seasonally during the spring and summer months of the southern hemisphere despite its subtropical distribution. It is one of only three sengi species known to breed seasonally. Fourteen male E. myurus were subjected to either long-day (LD; 16L:8D) or short-day (SD; 8L:16D) photoperiods and the photoperiodic effects on the testes, testosterone concentration and body mass were examined. Testicular volume and mass, seminiferous tubule diameter as well as body mass were not significantly different between LD and SD conditions. However, plasma testosterone concentration was significantly lower in males on LD compared to SD photoperiods. Male E. myurus may not use photoperiod as a cue to control seasonal reproductive changes. Other environmental factors such as temperature, rainfall, food abundance or social factors are possibly influencing seasonal reproduction in this species.A South African Research Chair of Mammalian Behavioural Ecology and Physiology awarded to Nigel C. Bennett by the Department of Science and Technology and the South African National Research Foundation (NRF) and K. Medger acknowledges a doctoral grant from the NRF.http://www.nrcresearchpress.com/journal/cjzZoology and Entomolog