Teasing apart socially-induced infertility in non-reproductive female Damaraland mole-rats, Fukomys damarensis (Rodentia: Bathyergidae)

A comprehensive profile of reproductive hormones in eusocial Damaraland mole-rats (Fukomys damarensis)

In species where sociality and group cohesion are primarily determined by the maintenance of a reproductive division of labour and cooperative behaviours, the eusocial Damaraland mole-rat (Fukomys damarensis) presents a model which provides behavioural and endocrine distinctions between sex (males and females) and reproductive class (breeders and non-breeders). Although previous studies have demonstrated the endocrine aspects of reproductive suppression and behaviour in Damaraland mole-rats, they have focused on one hormone separately and on different conspecifics and samples across time. Unfortunately, this could introduce extrinsic biases when using these studies to compile complete hormonal profiles for comparisons. This study, therefore, set out to obtain a profile of the reproductive hormones from breeding and non-breeding male and female Damaraland mole-rats at a single point in time, from which circulating plasma prolactin and urinary progesterone, testosterone, and cortisol were measured. As expected, plasma prolactin and urinary cortisol did not differ between the breeders and non-breeders. However, breeders (both male and female) possessed increased urinary testosterone and progesterone concentrations compared to their non-breeding counterparts. These results, in conjunction with the variation in the expression of the respective hormonal receptors within the brains of breeders and non-breeders suggest that elevated testosterone and progesterone in breeders establish a neural dominance phenotype, which ultimately aids in controlling breeding activities. This study has emphasised the need for holistic, comprehensive profiling of reproductive endocrine systems.

Gene expression pattern of Kisspeptin and RFamide-related peptide (Rfrp) in the male Damaraland mole-rat hypothalamus

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 anovulatory. Similarly, male subordinates within the colony show no sexual behaviour although they have functional gonads and do not differ from reproductive males in circulating levels of pituitary hormones and testosterone. However, reproductive status affects the neuroendocrine phenotype of males with breeders possessing increased mRNA expression of androgen and progesterone receptors compared to non-breeders in several forebrain regions implicated in the regulation of reproductive behaviour. The RFamide peptides kisspeptin and RFRP-3, encoded by the Kiss1 and Rfrp gene, are considered potent regulators of gonadotropin release. In females, reproductive inhibition is associated with reduced Kiss1 expression within the arcuate nucleus (ARC) and increased Rfrp expression in the anterior hypothalamus. To assess whether differential gene expression of Kiss1 and Rfrp underlies the difference in reproductive behaviour of males, we studied the expression of both genes by means of in situ hybridisation in wild-caught male Damaraland mole-rats with different reproductive status. The distribution of Kiss1 and Rfrp within the hypothalamus was found to be similar to females. Quantification of the Kiss1 hybridisation signal revealed no significant differences in relation to reproductive status. However, there was a significant positive correlation between testis mass and the number of Kiss1-expressing cells in the ARC and the mRNA content per cell, respectively. Analysis of the Rfrp hybridisation signal along the rostro-caudal extent of the hypothalamus revealed that non-reproductive males possessed an increased number of Rfrp-expressing cells at the level of the dorsomedial hypothalamic nucleus (DMH) than reproductive males. These data suggest the Kiss1 expression within the ARC is not associated with reproductive quiescence in subordinate males but instead, inhibitory effects may be mediated by Rfrp-expressing cells in the DMH.

Ovulation mitigates fatty liver associated with reproductive suppression and oxidative stress in Damaraland mole-rats (Fukomys damarensis)

Oxidative damage is often linked to reproduction; however, reproducing female Damaraland mole-rats (Fukomys damarensis) exhibit a reduction in oxidative damage relative to their non-reproductive, anovulatory, cohorts. Specifically, liver concentrations of malondialdehyde, a biomarker for lipid peroxidation, are significantly lower in reproducing females. We examined liver histology in reproductive, anovulatory and recently ovulating non-reproductive females, demonstrating an accumulation of lipid droplets only in the livers of anovulatory females and no fibrosis, cell death or inflammatory infiltrates in any group. Our observations suggest that anovulatory females experience a form of non-alcoholic fatty liver disease, which is reversed once they commence ovulation. We propose hormonal interactions that may underlie our observations.

Female-female reproductive suppression: impacts on signals and behavior

Female-female reproductive suppression is evident in an array of mammals, including rodents, primates, and carnivores. By suppressing others, breeding females can benefit by reducing competition from other females and their offspring. There are neuroendocrinological changes during suppression which result in altered behavior, reproductive cycling, and communication. This review, which focuses on species in Rodentia, explores the current theoretical frameworks of female-female reproductive suppression, how female presence and rank impacts reproductive suppression, and some of the proposed mechanisms of suppression. Finally, the understudied role of olfactory communication in female-female reproductive suppression is discussed to identify current gaps in our understanding of this topic.

Molecular detection and characterization of novel haemotropic Mycoplasma in free-living mole rats from South Africa

The importance of haemotropic Mycoplasma (haemoplasma) infections to animal and human health is increasingly recognised. Although wild rodents are known to host these bacteria, haemoplasma prevalence and diversity in small mammals is under-documented, globally. This is due to the reliance on molecular approaches to detect these unculturable, obligate bacteria and to a paucity of assays targeting informative gene regions. We attempted to address these challenges by evaluating the performance of three 16S rRNA PCR assays for detecting Mycoplasma in four African mole-rat species of the family Bathyergidae. This was achieved by screening DNA samples prepared from lung and liver samples of 260 bathyergids, sampled from natural and urban landscapes in the Western Cape Province with one published and two novel conventional PCR assays. Sequence-confirmed Mycoplasma presence guided calculations of the relative sensitivity and specificity of the assays and revealed that 26.5% of the rodents were haemoplasma-positive. Bathyergus suillus sampled near an informal human settlement had a significantly higher infection rate (42%) than the three bathyergid species sampled from natural settings, for which PCR-positivity ranged from 0% to 36%. The 16S rRNA gene phylogeny identified the presence of six Mycoplasma strains in bathyergids that form a novel monophyletic lineage belonging to the haemofelis group, with 16S rRNA and Rnase P gene phylogenies indicating that the bathyergid-associated haemoplasmas were novel and closely related to Mycoplasma coccoides. Assay sensitivity ranged from 60.3% to 76.8% and specificity from 94.8% to 100% and both were highest for the novel assay targeting a ~ 300 bp region of the 16S rRNA gene. Results confirm the presence of novel haemoplasma strains in bathyergid species from South Africa and emphasise the need for expanded studies on haemoplama prevalence, diversity, and transmission routes in other small mammal species from this biodiverse region.

Stress in groups: Lessons from non-traditional rodent species and housing models

A major feature of life in groups is that individuals experience social stressors of varying intensity and type. Social stress can have profound effects on health, social behavior, and ongoing relationships. Relationships can also buffer the experience of exogenous stressors. Social stress has most commonly been investigated in dyadic contexts in mice and rats that produce intense stress. Here we review findings from studies of diverse rodents and non-traditional group housing paradigms, focusing on laboratory studies of mice and rats housed in visible burrow systems, prairie and meadow voles, and mole-rats. We argue that the use of methods informed by the natural ecology of rodent species provides novel insights into the relationship between social stress, behavior and physiology. In particular, we describe how this ethologically inspired approach reveals how individuals vary in their experience of and response to social stress, and how ecological and social contexts impact the effects of stress. Social stress induces adaptive changes, as well as long-term disruptive effects on behavior and physiology.

Subterranean Mammals: Reservoirs of Infection or Overlooked Sentinels of Anthropogenic Environmental Soiling?

Global reports of emergent pathogens in humans have intensified efforts to identify wildlife reservoirs. Subterranean mammals, such as bathyergid mole rats, are largely overlooked, despite their high-level exposure to soil-dwelling microbes. Initial assessment of bathyergid reservoir potential was determined using a broad-range 16S rRNA PCR approach, which revealed an 83% PCR-positivity for the 234 bathyergid lung samples evaluated. The presence of the Bacillus cereus complex, a ubiquitous bacterial assemblage, containing pathogenic and zoonotic species, was confirmed through nucleotide sequencing, prior to group- and species-specific PCR sequencing. The latter allowed for enhanced placement and prevalence estimations of Bacillus in four bathyergid species sampled across a range of transformed landscapes in the Western Cape Province, South Africa. Two novel Bacillus strains (1 and 2) identified on the basis of the concatenated 16S rRNA-groEL-yeaC data set (2066 nucleotides in length), clustered with B. mycoides (ATCC 6462) and B. weihenstephanensis (WSBC 10204), within a well-supported monophyletic lineage. The levels of co-infection, evaluated with a groEL strain-specific assay, developed specifically for this purpose, were high (71%). The overall Bacillus presence of 17.95% (ranging from 0% for Georychus capensis to 45.35% for Bathyergus suillus) differed significantly between host species (χ² = 69.643; df = 3; P < 0.05), being significantly higher in bathyergids sampled near an urban informal settlement (χ² = 70.245; df = 3; P < 0.05). The results highlight the sentinel potential of soil-dwelling mammals for monitoring anthropogenically introduced, opportunistic pathogens and the threats they pose to vulnerable communities, particularly in the developing world.