Effects of season and social status on gonadal function in social Natal mole-rats

Oosthuizen, Maria K.; Viljoen, Hermien; Bennett, Nigel C.

doi:10.1644/08-mamm-a-368.1

Cited by 3 publications

(3 citation statements)

References 54 publications

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“…The similar germ cell proliferation among social states provides evidence against the hypothesis that social suppression limits the speed of the spermatogenic process, despite lower androgen levels in subordinates [39,52]. This is consistent with studies in social mole rats (Cryptomys hottentotus natalensis), which found that spermatogenesis occurs in non-reproductive males, despite low testosterone and sperm motility [53], and studies in mice show that the maintenance of spermatogenesis requires lower androgen levels than does the initiation of spermatogenesis [54]. Nonetheless, an increase in B-type spermatogonial stage frequency in A males, and an overall correlation between GSI and B type spermatogonia stage frequency, may reflect an increased investment in the initiation of spermatogenesis in A males, even as relative proliferation remains constant across social status.…”

Section: Discussionsupporting

confidence: 86%

Subordinate male cichlids retain reproductive competence during social suppression

2011

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Subordinate males, which are excluded from reproduction often save energy by reducing their investment in sperm production. However, if their position in a dominance hierarchy changes suddenly they should also rapidly attain fertilization capability. Here, we asked how social suppression and ascension to dominance influences sperm quality, spermatogenesis and reproductive competence in the cichlid Astatotilapia burtoni, where reproduction is tightly coupled to social status. Dominant territorial (T) males are reproductively active while subordinate non-territorial (NT) males are suppressed, but given the opportunity, NT males will perform dominance behaviours within minutes and attain T male testes size within days. Using the thymidine analogue 5-bromo-2-deoxyuridine (BrdU) to label germ cell proliferation, we found that the spermatogenic cycle takes approximately 11 -12 days, and social status had no effect on proliferation, suggesting that spermatogenesis continues during reproductive suppression. Although sperm velocity did not differ among social states, NT males had reduced sperm motility. Remarkably, males ascending in status showed sperm motility equivalent to T males within 24 h. Males also successfully reproduced within hours of social opportunity, despite four to five weeks of suppression and reduced testis size. Our data suggest that NT males maintain reproductive potential during suppression possibly as a strategy to rapidly improve reproductive fitness upon social opportunity.

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Section: Discussionsupporting

confidence: 86%

Subordinate male cichlids retain reproductive competence during social suppression

2011

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“…Significantly larger absolute and/or relative testicular volume and/or testicular mass in breeders compared to non-breeders have been reported for several social bathyergids with reproductive skew: Cryptomys hottentotus natalensis during summer [ 51 ], Fukomys damarensis [ 15 , 32 ], and Heterocephalus glaber [ 13 , 15 ]. No significant difference in the testicular size between the two male groups has been found in Cryptomys hottentotus hottentotus [ 52 ] and Cryptomys hottentotus natalensis during the winter [ 51 ]. In contrast to Maswanganye et al [ 32 ], Nice and colleagues [ 53 ] did not find a significant difference in the testicular mass between breeders and non-breeders of Fukomys damarensis .…”

Section: Discussionmentioning

confidence: 99%

Non-Breeding Eusocial Mole-Rats Produce Viable Sperm—Spermiogram and Functional Testicular Morphology of Fukomys anselli

et al. 2016

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Ansell’s mole-rats (Fukomys anselli) are subterranean rodents living in families composed of about 20 members with a single breeding pair and their non-breeding offspring. Most of them remain with their parents for their lifetime and help to maintain and defend the natal burrow system, forage, and care for younger siblings. Since incest avoidance is based on individual recognition (and not on social suppression) we expect that non-breeders produce viable sperm spontaneously. We compared the sperm of breeding and non-breeding males, obtained by electroejaculation and found no significant differences in sperm parameters between both groups. Here, we used electroejaculation to obtain semen for the first time in a subterranean mammal. Spermiogram analysis revealed no significant differences in sperm parameters between breeders and non-breeders. We found significantly larger testes (measured on autopsies and on living animals per ultrasonography) of breeders compared to non-breeders (with body mass having a significant effect). There were no marked histological differences between breeding and non-breeding males, and the relative area occupied by Leydig cells and seminiferous tubules on histological sections, respectively, was not significantly different between both groups. The seminiferous epithelium and to a lesser degree the interstitial testicular tissue are characterized by lesions (vacuolar degenerations), however, this feature does not hinder fertilization even in advanced stages of life. The continuous production of viable sperm also in sexually abstinent non-breeders might be best understood in light of the mating and social system of Fukomys anselli, and the potential to found a new family following an unpredictable and rare encounter with an unfamiliar female (“provoked or induced dispersal”). Apparently, the non-breeders do not reproduce because they do not copulate but not because they would be physiologically infertile. The significantly increased testes volume of breeding males (compared to non-breeders) is in agreement with previously found higher testosterone levels of breeders.

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“…Nevertheless, the majority of the social species breed aseasonally, with pregnant females captured at all times of the year (Bennett and Jarvis, 1988b;Burda, 1989;Brett, 1991;Bennett et al, 1994a;Bennett and Aguillar, 1995;Oosthuizen et al, 2008b;Sichilima et al, 2008Sichilima et al, , 2011Hart et al, 2021a). In both seasonally and aseasonally breeding species, there are no seasonal differences in gonadal histology, gonadal hormones, LH responses to GnRH challenges, or the GnRH system in the brain (Spinks et al, 1997(Spinks et al, , 1999(Spinks et al, , 2000Van der Walt et al, 2001;Du Toit et al, 2006;Oosthuizen et al, 2008bOosthuizen et al, , 2010b.…”

Section: Seasonal Breedingmentioning

confidence: 99%

Clocks Ticking in the Dark: A Review of Biological Rhythms in Subterranean African Mole-Rats

Oosthuizen

Bennett

2022

Front. Ecol. Evol.

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Biological rhythms are rhythmic fluctuations of biological functions that occur in almost all organisms and on several time scales. These rhythms are generated endogenously and entail the coordination of physiological and behavioural processes to predictable, external environmental rhythms. The light-dark cycle is usually the most prominent environmental cue to which animals synchronise their rhythms. Biological rhythms are believed to provide an adaptive advantage to organisms. In the present review, we will examine the occurrence of circadian and seasonal rhythms in African mole-rats (family Bathyergidae). African mole-rats are strictly subterranean, they very rarely emerge aboveground and therefore, do not have regular access to environmental light. A key adaptation to their specialised habitat is a reduction in the visual system. Mole-rats exhibit both daily and seasonal rhythmicity in a range of behaviours and physiological variables, albeit to different degrees and with large variability. We review previous research on the entire circadian system of African mole-rats and discuss output rhythms in detail. Laboratory experiments imply that light remains the strongest zeitgeber for entrainment but in the absence of light, animals can entrain to ambient temperature rhythms. Field studies report that rhythmic daily and seasonal behaviour is displayed in their natural habitat. We suggest that ambient temperature and rainfall play an important role in the timing of rhythmic behaviour in mole-rats, and that they likely respond directly to these zeitgebers in the field rather than exhibit robust endogenous rhythms. In the light of climate change, these subterranean animals are buffered from the direct and immediate effects of changes in temperature and rainfall, partly because they do not have robust circadian rhythms, however, on a longer term they are vulnerable to changes in their food sources and dispersal abilities.

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Effects of season and social status on gonadal function in social Natal mole-rats

Cited by 3 publications

References 54 publications

Subordinate male cichlids retain reproductive competence during social suppression

Subordinate male cichlids retain reproductive competence during social suppression

Non-Breeding Eusocial Mole-Rats Produce Viable Sperm—Spermiogram and Functional Testicular Morphology of Fukomys anselli

Clocks Ticking in the Dark: A Review of Biological Rhythms in Subterranean African Mole-Rats

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