Influence of breeding season and reproductive status on male reproductive characteristics in the common mole-rat, Cryptomys hottentotus hottentotus A. C. Spinks, G. Van der Horst and N. C. Bennett Department of Zoology, University of Cape Town, Rondebosch, 7700, Cape Town, South Africa, 1Department of Physiological Sciences, University of Western Cape, Bellville, 7535, South Africa, Department of Zoology and Entomology, University of Pretoria, Pretoria, 0002, South Africa The effects of breeding season and reproductive status on male reproduction were investi- gated 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 mainten- ance 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 reproduc- tion in male common mole-rats is more typical of social suppression in male mammals. Introduction The common mole-rat, Cryptomys hottentotus hottentotus, is a social subterranean rodent, and lives in colonies of two to 14 individuals (Bennett, 1989). It is a widely distributed species occurring in both mesic and xeric areas of the southern African subregion (Skinner and Smithers, 1990). The common mole-rat is apparently unique among the social bathyergids in exhibiting seasonal reproduction (Bennett et al, 1991; Jarvis and Bennett, 1991; N. C. Bennett and J. U. M. Jarvis, personal communi¬ cation). Long-term mark-recapture studies revealed that birth of offspring in this species is restricted to the Southern Hemisphere summer period (late November to January), during which time a maximum of two litters may be reared (Skinner and Smithers 1990; Jarvis and Bennett, 1991; A. C. Spinks, N. C. Bennett and C. M. Rosenthal, unpublished). Gestation in common mole-rats lasts approximately 55—66 days (Bennett 1989), suggesting that most mating probably occurs between September and early November. The reproductive periodicity evident in the common mole- rat is typical of both surface-dwelling and subterranean mam¬ mals inhabiting seasonal environments (see for example, Wehrenberg and Dyrenfurth, 1983; Gorman and Stone, 1990; Parreira and Cardoso, 1993; Kaplan and Mead, 1994; Page et al, 1994). Annual alterations in environmental factors, modified by social factors, provide the proximate cues for such reproductive periodicity (Clarke, 1981; Ims, 1990; Bronson and Heideman, 1994; Turek and Van Cauter, 1994). In male mammals the non-reproductive period is typically characterized by testicular regression and the cessation of spermatogenesis (Clarke, 1981). In contrast, during the reproductive period, seasonal exteroceptive factors activate the testes through the anterior pituitary, resulting in sexual recrudescence (Clarke, 1981). Interpretations of seasonal manifestations on common mole- rat male reproduction may be confounded by the reproductive division of labour prevalent in C. h. hottentotus colonies. Reproduction is typically restricted to the largest male and female in a colony, while the remaining colony members (both male and female) are reproductively quiescent (Bennett, 1989, 1992; Rosenthal et al, 1992). Consequently, any manifestations of reproductive status on male reproductive characteristics are likely to obscure the effects of reproductive periodicity. The common mole-rat provides a unique model to investi¬ gate the effects of both breeding season and reproductive status on the reproductive physiology of a co-operatively breeding rodent. The aims of this study were to investigate these effects on male reproduction, using data on testicular anatomical and histological morphometrics, and selected sperm parameters. Received 25 March 1996. Downloaded from Bioscientifica.com at 06/15/2020 07:40:26PM via free access