Oligospermia and azoospermia in non-reproductive male Damaraland mole-ratsCryptomys damarensis (Rodentia : Bathyergidae)

The relationship between reproductive status and reproductive physiology wa s investigated in male Damaraland mole-rats Cryptomys damarensis, an eusoci al rodent that exhibits a marked reproductive division of labour. Testicula r anatomical and histological morphometrics, selected sperm motion paramete rs and measurements of circulating plasma testosterone were studied in 44 m ales (17 reproductive and 27 non-reproductive). Reproductive males were sig nificantly larger than non-reproductive males. Testicular mass of reproduct ive males, corrected for body mass, was significantly larger than in non-re productives. However, corrected testicular volume did not vary significantl y between the two groups. Circulating plasma testosterone concentrations of reproductives and non-reproductives were not significantly different (repr oductive males 201.5 +/- 56.5 pg/l vs 187.5 +/- 91 pg/l for non-reproductiv e males). The quality of sperm was measured by the percentage of spermatozo a produced and the amount of immature sperm, and differed between the two g roups. Reproductive males produced a greater proportion of motile sperm (77 .8%) than non-reproductives (56.3%). Non-reproductive males were characteri zed by a greater proportion of immature sperm in the epididymis (79%) than the reproductives (25%). Interestingly, the spermatozoa of reproductive mal es were characterized by a greater percentage of head and tail defects. Oli gospermia may be the result of a reduction in circulating follicle stimulat ing hormone, which acts upon the Sertoli cells of the seminiferous tubules, that in turn may be due to a lack of an opportunity to mate while in the c onfines of the colony in this obligate outbreeder.