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Co-operatively breeding mammals often exhibit a female reproductive skew and suppression of the subordinate non-breeding group members. According to evolutionary theory and the immunity–fertility axis, an inverse relationship between reproductive investment and survival (through immunocompetence) is expected. As such, this study investigated if a trade-off between immunocompetence and reproduction arises in two co-operatively breeding African mole-rat species, namely the Damaraland mole-rat (Fukomys damarensis) and common mole-rat (Cryptomys hottentotus hottentotus), which possess female reproductive division of labour. This study also attempted to investigate the relationship between the immune and endocrine systems in Damaraland mole-rats. There was no trade-off between reproduction and immunocompetence in co-operatively breeding African mole-rat species, and in the case of the Damaraland mole-rats, breeding females (BFs) possessed increased immunocompetence compared with non-breeding females (NBFs). Furthermore, the increased levels of progesterone possessed by Damaraland mole-rat BFs compared with NBFs appear to be correlated to increased immunocompetence. In comparison, BF and NBF common mole-rats possess similar immunocompetence. The species-specific differences in the immunity–fertility axis may be due to variations in the strengths of reproductive suppression in each species. This article is part of the theme issue 'Evolutionary ecology of inequality'. [ABSTRACT FROM AUTHOR]

African mole‐rats (family Bathyergidae) show a wide variety of social organization, from strictly solitary to highly social. Within the family, both modes of ovulation, spontaneous and induced, have been found and are thought to relate to seasonality of reproduction and opportunities for dispersal. Damaraland mole‐rats (Fukomys damarensis) are cooperative breeders, which breed year‐round and exhibit high reproductive skew. Reproduction is monopolized by a single female (queen) in each group, and non‐reproductive females in the presence of the queen are anovulatory. The species was previously described as being a spontaneous ovulator; however, subsequent attempts to determine the length of the oestrous cycle have failed. Therefore, we revisited this subject by studying the urinary progesterone and oestradiol profiles over a period of 7 weeks and the ovarian histology of females kept under different social conditions. The first experiment shows that average urinary progesterone concentrations of breeder females paired with a vasectomized male (full physical contact) are significantly higher than those of breeder females kept singly, non‐breeder females kept singly and non‐breeder females kept within their natal group. In the second experiment, we subjected females consecutively to different experimental conditions: full physical contact (stage 1), isolation (stage 2), non‐physical contact (stage 3) and measured their steroid hormone profiles. The females showed elevated concentrations of urinary progesterone during the phase of full physical contact and basal concentrations during the subsequent single housing phase. Correspondingly, no corpora lutea of ovulation were found in the ovaries of these females in the latter phase. During stage 3, in which females were separated from a male by wire mesh (non‐physical contact), one of three females showed elevated progesterone and oestradiol concentrations throughout the sampling period and analysis of ovarian histology revealed a corpus luteum. Together, these results support the view that Damaraland mole‐rats are induced ovulators, in which non‐coital male cues are able to induce ovulation. [ABSTRACT FROM AUTHOR]

Ansell's mole-rat, Fukomys anselli, is a social subterranean mammal and exhibits an extreme reproductive division of labour. Reproduction in the colony is restricted usually to a single female. Complete colonies captured throughout an entire calendar year were euthanased and the histology of the gonads and plasma hormone concentrations were measured in reproductive and non-reproductive members of both sexes. In males, the circulating levels of testosterone were significantly higher in the reproductive male than the non-reproductive males. The mean testes mass for the reproductive males corrected for body mass was not significantly greater than that of the non-reproductive male. Similarly, the mean testes volume of reproductive males was not greater than that for the non-reproductive males but the seminiferous tubule diameter was significantly greater in the reproductive males than the non-reproductive males. Reproductive females characteristically possessed corpora lutea of ovulation and pregnancy in their ovaries and this was met with much higher progesterone concentrations in the reproductive females 34 nmol/L compared with 4 nmols/L in the non-reproductive females. In contrast, non-reproductive females showed a complete range of follicular genesis, but they did not possess corpora lutea of ovulation or pregnancy, in turn they show depressed progesterone concentrations. The current evidence suggests that in Ansell's mole-rats, the non-reproductive males and females refrain from sexual activity by being subordinate and moreover, related to the breeding pair. [ABSTRACT FROM AUTHOR]

Many mammal species reproduce seasonally because of annual fluctuations in temperature, rainfall and photoperiod in often nutritionally challenging habitats. The reproductive biology of many small southern African mammals is largely unknown and in critical need of study. We investigated the breeding pattern of the female spiny mouse ( Acomys spinosissimus) from South Africa. We examined the ovarian development, follicular growth, circulating plasma progesterone concentrations and the reproductive status of wild-caught adult female spiny mice sampled over a 12-month period while also correcting for body mass and age. From these data, we conclude that female A. spinosissimus breed seasonally. The main breeding season of the spiny mouse is between September and January, with plasma progesterone concentrations being elevated, ovarian volume and primary, secondary, tertiary and Graafian follicle numbers as well as the corpora body number being the highest and pregnancies occurring during this period. Females were reproductively inactive from February through to August. The breeding season coincides with the onset of the rainy season in the habitat, which starts around September and ends in April. Rainfall, in association with an increase in primary productivity and hence higher food availability, might be the most important factor shaping reproduction in the female spiny mouse. [ABSTRACT FROM AUTHOR]

The giant mole-rat Fukomys mechowii is a cooperatively breeding, subterranean rodent inhabiting the Miombo woodland and savanna of south-central Africa, with reproduction occurring throughout the year. Across species within the family Bathyergidae, ovulation can be either induced by mating or spontaneous and the particular mechanism may correlate with patterns of seasonality, dispersal and opportunities for mating. We investigate the control of ovulation in F. mechowii, a species closely related to a spontaneously ovulating species but found in a habitat more typical of mole-rats with induced ovulation. Six wild-caught, non-reproductive females were removed from their natal colonies and non-invasively monitored for ovarian cyclicity by measuring urinary progesterone every 2 days, over 217 days. All six females had elevated progesterone profiles indicative of the luteal phase of the ovarian cycle, whether singly housed, separated from a male by a mesh screen (i.e. non-physical contact), or paired with a vasectomised male (full physical contact), although progesterone concentrations were significantly enhanced in the latter condition. Together with observations that male penile morphology is similar to other spontaneously ovulating bathyergids, these results strongly suggest that while ovarian cyclicity may occur spontaneously in F. mechowii, the presence of a male may have an additional stimulatory effect on ovulation. Comparative phylogenetic analysis revealed a positive correlation between seasonality in breeding and induced ovulation. Furthermore, a likelihood-based reconstruction suggests that induced ovulation is the ancestral state for the Bathyergidae and that this trait has been convergently lost in at least two lineages, giving rise to a spontaneous mode of ovulation. [ABSTRACT FROM AUTHOR]

The distribution of ovulation patterns and penile ornamentation in mammals is thought to be shaped by sexual selection. Alternatively, ovulation patterns have been linked to factors such as phylogeny, social system and ecological constraints but no conclusive pattern has emerged. African mole-rats exhibit a unique range of social organizations and experience diverse ecological conditions (i.e. rainfall patterns), with various species exhibiting either induced or spontaneous ovulation in addition to a corresponding variation of penile ornamentation. Investigations of members of this family conducted so far do not allow conclusions to be drawn about the importance of phylogenetic versus ecological constraints for the evolution of ovulation patterns because all species of the genus Cryptomys studied occur in mesic habitats and exhibit induced ovulation. In contrast, the one representative of the genus Fukomys is a spontaneous ovulator that occurs in arid habitats. The current study aimed to elucidate the factors creating the observed ovulation pattern by using a species within a genus for which so far only spontaneous ovulation has been recorded, but unlike the other species with known ovulation mechanisms of this genus, it occurs in a mesic environment. Previously, non-reproductive Ansell's mole-rat Fukomys anselli females were housed individually for a period of 6 weeks before being housed either alone, in chemical or physical contact with a male. Progesterone profiles generated from urine samples collected throughout the study did not differ significantly either before or after the pairing or between the experimental groups, suggesting that they ovulate spontaneously. This was supported by the lack of penile ornamentation found in males of this species. The results suggest that phylogenetic rather than ecological constraints determine the ovulation patterns observed in social bathyergids. [ABSTRACT FROM AUTHOR]

The reproductive cycle of mammals can be inhibited by 2 factors, seasonal breeding and dominance control, both potentially important in mole-rats. The gonads and gonadal steroids of dominant (reproductive) and subordinate (nonreproductive) Natal mole-rats (Cryptomys hottentotus natalensis) were investigated to determine the effects of season and social status on reproduction within natal colonies. We found no seasonal differences in concentrations of gonadal steroids of male or female mole-rats. Similarly, the gonadal histology and volume showed no seasonal differences. These results, together with the presence of fetuses, confirm the potential for breeding throughout the year. Reproductive and nonreproductive mole-rats display comparable testosterone and estrogen concentrations in males and females, respectively. Follicular development and the presence and number of sperm in nonreproductive animals suggest that the reproductive quiescence in nonreproductive animals is likely to result from behavioral interference of dominant animals or incest avoidance (or both). Urinary progesterone concentrations of reproductive females were significantly higher than those of nonreproductive females. Although follicular development in nonreproductive females proceeds to the level of Graafian follicles, the number of these follicles present in nonreproductive females was significantly less than that in reproductive females. The reproductive physiology of the Natal mole-rat compares with other loosely social mole-rat species inhabiting mesic areas. [ABSTRACT FROM AUTHOR]

Urinary testosterone concentrations in males and urinary progesterone and oestradiol concentrations in females were measured in the Cape mole-rat (Georychus capensis) and compared for the summer and winter periods. The Cape mole-rat breeds seasonally, with sexual activity and subsequent pregnancy recorded during the winter months in the southern hemisphere. Despite the fact that it has a distinct breeding season, seasonal differences in urinary hormone concentrations of both male and female Cape mole-rats were not statistically significant. This finding supports the notion the Cape mote-rat may have the opportunity to operate as an opportunistic breeder if fortuitous environmental conditions arise, such as unseasonal rainfall, occurring at these normally non-favourable times of the year. [ABSTRACT FROM AUTHOR]

The Cape dune mole-rat (Bathyergus suillus) is a solitary, seasonally breeding, rodent mole. Body mass, reproductive tract morphometrics, ovarian histology, and plasma estrogen and progesterone concentrations were measured in females during 1 calendar year to elucidate if this species had an inclination toward seasonal breeding. Qualitative analyses of ovarian histology revealed that females retain the potential for ovulation and subsequent production of corpora lutea from early austral winter to spring (June-October). Seasonal differences were found in ovarian morphometrics and hormone concentrations that are associated with follicular activation from April and subsequent conceptions from June to November. Body mass, reproductive tract morphometrics, testicular histology, and plasma testosterone concentrations were obtained for males over the period of 1 calendar year. There was a gradual increase in seminiferous tubule diameter from May to October, which was mirrored by fluctuations in testosterone concentration. The current data support a strong seasonality to reproduction in the Cape dune mole-rat from April to October with a peak that is linked to the period of maximal rainfall within the distributional range of this species. [ABSTRACT FROM AUTHOR]