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Are non-reproductive male highveld mole-rats, Cryptomys hottentotus pretoriae physiologically suppressed while in the confines of the natal colony?

Authors

  • L. Janse van Rensburg,

    1. Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa
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  • N. C. Bennett,

    Corresponding author
    1. Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa
      *All correspondence to: N. C. Bennett, Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa
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  • M. van der Merwe,

    1. Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa
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  • A. S. Schoeman,

    1. Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa
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  • J. Brinders

    1. Department of Veterinary Physiology, Onderstepoort, Pretoria 0002, South Africa
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*All correspondence to: N. C. Bennett, Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa

Abstract

The highveld mole-rat, Cryptomys hottentous pretoriae is a social, subterranean, co-operative breeder with a high reproductive skew. The relationship between reproductive status and reproductive physiology in male highveld mole-rats was investigated. Testicular morphometrics, histological parameters, plasma testosterone concentrations and sperm motility parameters were studied in 31 males (14 reproductive and 17 non-reproductive males). Reproductive males were significantly larger than non-reproductive males, with testicular mass and volume corrected for body mass considerably larger for the reproductive males. Circulating plasma testosterone concentrations of reproductive males were not significantly higher than non-reproductive males (reproductive males 10.3±1.8 nmol l−1vs non-reproductive males 7.3±1.74 nmol l−1). Sperm motility parameters were measured, but no significant differences were found between reproductive and non-reproductive males. All 14 reproductive males had motile sperm, whereas 13 of the 17 (76%) of non-reproductive males possessed motile sperm. A typical ejaculate of a reproductive male contains 48.3% motile sperm characterized by a high percentage of flagellar defects, whereas the non-reproductive male has an ejaculate containing 45.6% motile sperm with a high percentage of head defects. It is apparent that non-reproductive males are not physiologically suppressed from reproducing. Moreover, the non-reproductive males are excluded from incestuous matings as a result of being the offspring of the reproductive female.

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