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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'.

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., (© 2018 British Society for Neuroendocrinology.)

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.

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.

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.

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.

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.

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.

The effects of breeding season and reproductive status on male reproduction were investigated in the common mole-rat (Cryptomys hottentotus hottentotus), a co-operatively breeding rodent that exhibits seasonal reproduction and a reproductive division of labour. Testicular anatomical and histological morphometrics, and selected sperm parameters were studied in 50 males from 17 wild caught colonies. Males exhibited no apparent manifestation of season on testicular activity: spermatogenesis and sperm quality (motility and percentage normal morphology) were similar in the reproductively active and inactive periods. This maintenance of reproductive activity during the non-reproductive period is essential in C. h. hottentotus males, as this period coincides with the period of maximal dispersal opportunities. Such reproductive activation in dispersing males may aid intersexual recognition, and assist pair-bond formation or successful assimilation into foreign colonies, thereby facilitating later outbreeding. Consequently, outbreeding opportunities may be important determinants of reproductive activity in male common mole-rats, moderating seasonal effects. Reproductive and non-reproductive males revealed no differences in any of the testicular or sperm parameters studied. The absence of a physiologically well-defined suppression of reproduction in male common mole-rats is more typical of social suppression in male mammals.

Pituitary function in reproductive and nonreproductive colony members of Damaraland mole-rats, Cryptomys damarensis, was investigated by measuring the LH responses to single doses of 2 micrograms exogenous GnRH and physiological saline in 29 females and 37 males (31 of these animals from two entire colonies). In females, basal LH concentrations were significantly greater in reproductive (n = 9) than in nonreproductive animals (n = 11): 7.6 +/- 1.0 versus 4.3 +/- 0.6 miu ml-1, respectively (P < 0.001). Reproductive females had a significantly greater LH response to 2.0 micrograms GnRH (7.6 +/- 1.0 to 37.7 +/- 6.2 miu ml-1; n = 9) than did nonreproductive females (4.3 +/- 0.6 to 11.8 +/- 1.0 miu ml-1; n = 11, P < 0.001). In contrast, there was no significant difference in basal LH concentrations between reproductive (n = 8) and nonreproductive males (n = 20): 5.3 +/- 4.3 versus 3.2 +/- 1.2 miu ml-1, respectively. There was also no difference in LH response to the administration of 2.0 micrograms GnRH between reproductive and nonreproductive males (5.3 +/- 4.3 to 21.8 +/- 8.6 miu ml-1; n = 8; versus 3.2 +/- 1.2 to 21.1 +/- 8.5 miu ml-1; n = 21; P = 0.5). When the results from the two entire colonies were analysed separately, LH responses to GnRH in the 11 nonreproductive females were less than in the two reproductive females. In contrast, the response of two reproductive males in the colonies did not differ from that of 16 nonreproductive males, although these latter comparisons could not be validated statistically.(ABSTRACT TRUNCATED AT 250 WORDS)

This study aimed to assess the seasonal reproductive strategy occurring in the male Lesser Egyptian jerboa (Jaculus jaculus) and determine which environmental cues are responsible for initiating reproductive recrudescence. Body mass, morphometry of the reproductive tract, the histology of the testes and the circulating testosterone concentrations in wild male J. jaculus, from central Saudi Arabia, were studied over 12 consecutive months. Furthermore, sixteen additional males were collected and subsequently placed on either a short‐day (SD) or a long‐day (LD) light schedule under controlled laboratory conditions. Using these male reproductive parameters, we investigated the potential proximate environmental cues that may trigger the onset of reproduction. Unexpectedly, males were reproductively active during three out of the four seasons, namely autumn, winter and spring possibly due to the rainfall that fell at an unprecedented frequency and quantity during this time. However, we revealed the importance of other environmental triggers, namely photoperiod and ambient temperature, on the control of male reproduction in J. jaculus. Decreasing photoperiod (SD) and ambient temperature were observed to activate the reproductive system by increasing plasma testosterone concentration. The male Lesser Egyptian jerboa was found to exhibit a marked seasonal reproduction controlled by the environmental cues of ambient temperature and photoperiod. [ABSTRACT FROM AUTHOR]

Periods of reproduction are linked to changes in male behaviour, physiology and physical parameters. Although high androgen concentrations hold numerous advantages, especially during reproductive periods, chronically elevated androgen concentrations over long periods may be costly and thus need to be regulated. As such seasonal breeders will display temporary elevated androgen concentrations, increased testis levels and mating behaviour only during important reproductive periods. We studied a captive as well as a free-ranging population of the polygamous strepsirrhine primate, the African lesser bushbaby Galago moholi, to clarify the link between androgen concentration, reproductive behaviour and testis size and the importance of the two mating periods observed in the species. To monitor androgen patterns, we used faecal sampling and quantification of faecal androgen metabolites ( fAM). We additionally collected testicular measurements and behavioural data. G. moholi displayed a strong degree of reproductive seasonality, with maximum fAM concentration, testicular volume ( TV) and behavioural activity focused on the mating periods. In contrast to other studies, TV increased prior to fAM, with reproductive activity being initiated only when fAM concentrations reached high levels. Changes in TV and fAM concentrations were not significantly different between both mating periods. Based on the absence of a significant difference between mating seasons, it is likely that male G. moholi attempt to maximize their reproductive success by utilizing both mating periods equally. This study is the first to describe the reproductive endocrine pattern linked to physical changes and mating behaviour in any galago species, increasing our understanding of the reproductive biology of nocturnal, polygamous primates. [ABSTRACT FROM AUTHOR]

The East African root rat Tachyoryctes splendens (Rüppell, 1835) is a solitary subterranean rodent mole. The present study investigated breeding patterns in both sexes of T. splendens from data collected at monthly intervals over an entire calendar year. The study focused on the analyses from post-mortem examination of male and female East African root rats to assess the presence of foetuses, gonadal histology, reproductive tract morphometrics, measurement of gonadal steroids (plasma progesterone and oestradiol-17 β in females and testosterone in males) and field observations (i.e. the presence of infants, juveniles, subadults and lactating females). The objective of this study was to assess if the reproductive biology of root rats reflected the bimodal pattern of rainfall that is characteristic of East Africa. Rainfall has been suggested to trigger breeding in many subterranean rodents and as a consequence, this study aimed to assess the relationship between rainfall and reproductive characteristics of T. splendens. Peaks in mean gonadal mass, increases in concentration of reproductive hormones and the presence of graafian follicles and corpora lutea in the ovaries of females, and testes mass, seminiferous tubule diameter and testosterone titre mirrored the annual peaks of precipitation at the study area. Together with field observations of the temporal occurrence of pregnancies, infants, juveniles and subadults, the data show that T. spendens cues its breeding with the patterns of rainfall, such that offspring are born in the latter half of each rainy season, from April to July and November to December. [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]

Ansell's mole-rat, Fukomys anselli, is a cooperatively breeding bathyergid endemic to the Lusaka Province of Zambia. During a 12-month field study involving the capture of 33 colonies of mole-rats, the number of occupants, breeding females and sex ratio within colonies were recorded. While thirty of these social groups contained a single breeding queen, three were found to exhibit plural breeding among females, having two queens present simultaneously. Mean ± S.E.M. colony size was 8.7 ± 2.2 (range 6-16, n = 33 ). The occurrence of plural breeding and small group size is consistent with the predictions of the aridity food distribution hypothesis for social species inhabiting mesic habitats. The sex ratio of the population was skewed towards females at 1.2:1. The mean mass of adult males was 63.0 ± 18.3 g (range 36.7-110.3, n = 87) while that for adult females was 52.9 ± 11.8 g (range 35.1-77.8, n = 86). Pregnant and lactating females were found throughout the study period from February 2009 to February 2010, indicating an aseasonal pattern of breeding in this species. Autopsy of individuals (n = 288) from the 33 colonies revealed a total of 19 pregnant females. Nine of these were in the latter stages of pregnancy and mean litter size was determined as 2.7 pups (range 1-4). Collectively, these new data reveal that Fukomys anselli share many similarities in life history and reproductive traits with the phylogentically closely related giant Zambian mole-rat, Fukomys mechowii. [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]

While females are traditionally thought to invest more time and energy into parental care than males, males often invest more resources into searching and displaying for mates, obtaining mates and in male–male conflict. Solitary subterranean mammals perform these activities in a particularly challenging niche, necessitating energetically expensive burrowing to both search for mates and forage for food. This restriction presumably affects males more than females as the former are thought to dig longer tunnels that cover greater distances to search for females. We excavated burrow systems of male and female Cape dune mole rats Bathyergus suillus the, largest truly subterranean mammal, to investigate whether male burrows differ from those of females in ways that reflect mate searching by males. We consider burrow architecture (length, internal dimensions, fractal dimension of tunnel systems, number of nesting chambers and mole mounds on the surface) in relation to mating strategy. Males excavated significantly longer burrow systems with higher fractal dimensions and larger burrow areas than females. Male burrow systems were also significantly farther from one another than females were from other females' burrow systems. However, no sex differences were evident in tunnel cross-sectional area, mass of soil excavated per mound, number of mounds produced per unit burrow length or mass of soil excavated per burrow system. Hence, while males may use their habitat differently from females, they do not appear to differ in the dimensions of the tunnels they create. Thus, exploration and use of the habitat differs between the sexes, which may be a consequence of sex differences in mating behaviour and greater demands for food. [ABSTRACT FROM AUTHOR]

The Cape ground squirrel Xerus inauris is unusual among social mammals as it exhibits a low reproductive skew, being a facultative plural breeder with not all females breeding within a group. We investigated pituitary function to assess whether there was reproductive inhibition at the level of the pituitary and potentially the hypothalamus in breeding and non-breeding female Cape ground squirrels. We did so during the summer and winter periods by measuring luteinizing hormone (LH) responses to single doses of 2 g exogenous gonadotropin-releasing hormone (GnRH) and physiological saline administered to 42 females from 11 colonies. Basal LH concentrations of females increased in response to the GnRH challenge. Basal plasma LH concentrations were greater during winter, when most oestrus events are observed. However, we found no differences in plasma LH concentrations between breeding and non-breeding females. We showed that the anterior pituitary of non-breeding female ground squirrels is no less sensitive to exogenously administered GnRH than that of breeding females. We therefore concluded that the pituitary is no more active in breeding than non-breeding females. The lack of differentiation in response to GnRH suggests that either non-breeding females have ovaries that are less sensitive to LH or that they refrain from sexual activity with males through an alternative mechanism of self-restraint. [ABSTRACT FROM AUTHOR]

The Cape mole rat Georychus capensis is a solitary mole rat that inhabits the winter rainfall region of the Western Cape Province of South Africa. Circulating basal concentrations of luteinizing hormone (LH) were found to be significantly higher in the breeding season in both sexes. During both the breeding and non-breeding season, administration of exogenous gonadotropin-releasing hormone (GnRH) increased circulatory LH levels. The magnitude of the LH response to an overdose of exogenous GnRH both in and out of the breeding season in males and females was not significantly different. Typically, seasonally breeding species exhibit a down-regulation of the pituitary and reproductive functions out of the breeding season. It appears that there is no down-regulation of GnRH receptors at the level of the pituitary out of the breeding season, because the pituitary responds to an exogenous GnRH challenge equally both in and out of the breeding period. The Cape mole rat exhibits the potential for opportunistic breeding out of the breeding period, provided that environmental factors are favourable. This finding questions whether this mole rat is actually a seasonal breeder or whether reproduction is hindered by the ecological constraint of the lack of opportunities to burrow and find mates at certain 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]

Very little is known about the reproductive biology of the recently recognized Tete veld rat Aethomys ineptus. In the present study, we investigated the seasonality of reproduction in this newly recognized rodent using a number of histological and endocrinological parameters. Body mass, reproductive tract morphometrics, gonadal histology, and plasma testosterone concentrations in males and plasma oestradiol-17 β and progesterone concentrations in females were assessed from a population in the north-central part of South Africa over a 12-month period in order to ascertain the pattern of reproduction in the species. Seminiferous tubule diameters in 59 males were significantly larger between September and February relative to between March and August. Although spermatogenesis was prevalent in the southern hemisphere winter (June–August), the number of spermatozoa in the epididymides decreased in the southern hemisphere spring (September–November), summer (December–February) and autumn (March–May). Testicular mass relative to body mass and testicular volume regressed between May and September but exhibited recrudescence between September and April, whereas plasma testosterone concentrations increased significantly between September and February relative to between March and August. Ovarian histology of 67 females showed corpora lutea to be present throughout the year, but decreased in number during winter, whereas mean plasma progesterone concentration increased significantly between August and November and again between February and April. This bimodal pattern of progesterone concentration suggests that up to two litters per breeding season may be raised by the Tete veld rat. Gravid females were found between October and April, whereas gravid or lactating females were conspicuously absent between May and September. Collation of all these data suggests that the Tete veld rat is a seasonal breeder with reproduction confined predominantly to summer and autumn months of the southern hemisphere. However, the presence of follicular development in females and the presence of corpora lutea outside the breeding season imply that the Tete veld rat may undergo spontaneous ovulation. [ABSTRACT FROM AUTHOR]

Male Tete veld rats Aethomys ineptus and Namaqua rock mice A. namaquensis were independently subjected to a long photoperiod of 16L:8D and a short photoperiod of 8L:16D for 3 months in order to assess the effect of photoperiod on testicular function. Testicular parameters examined included testicular mass relative to body mass, testicular volume, seminiferous tubule diameters and changes in circulating plasma testosterone concentration. On a long day (LD) length, both species exhibited significantly higher testicular mass relative to body mass and testicular volume, and larger seminiferous tubule diameters. Circulating plasma testosterone concentrations in A. ineptus were not significantly different between the two photoperiodic treatments, but A. namaquensis showed significantly higher testosterone concentration in males on a LD length than on a short day (SD) length. This suggests that both A. ineptus and A. namaquensis are photoperiodically responsive to LDs. [ABSTRACT FROM AUTHOR]