Exposure to non-kin females rapidly affects testicular morphology in non-reproductive male Damaraland mole-rats

Damaraland mole-rats Fukomys damarensis are eusocial subterranean rodents that exhibit an extreme reproductive skew with one female and one or two males breeding. The non-reproductive individuals in the colony are reproductively suppressed, and yet show a rapid initiation of copulatory behaviour (within 1 h) when taken out of the colony and exposed to non-kin. Little is known about how these individuals can quickly become sexually active if the causes of suppression are removed. This study investigated circulating gonadotrophin concentrations [follicle stimulating hormone (FSH)] and testicular morphology and function in reproductive and non-reproductive male Damaraland mole-rats taken directly from their natal colonies and non-reproductive males that had been introduced to non-kin females outside their colony for 10 or 60 min. The main findings were that 60-min exposure males had a significantly heavier body mass-corrected testicular mass than reproductive males. In addition, the external seminiferous tubule diameter was significantly larger in reproductive males than in non-reproductive males, and the tubule lumen area was significantly greater in reproductive, 10 and 60-min exposure males than in non-reproductive males. Plasma concentrations of FSH were not different between the groups; however, the reproductive status significantly affected the area of testicular tissue stained immunopositive for the FSH receptor (FSH-R). Reproductive males had almost six times more FSH-R compared with non-reproductive males, and 60-min exposure males had eight times more FSH-R compared with non-reproductive males. In conclusion, the increase in the seminiferous tubular lumen area and the testicular FSH receptor content when non-reproductive male mole-rats come into contact with non-kin females indicates a rapid activation of testicular spermatogenic pathways to accompany the onset of copulatory behaviour, and is likely to be adaptive in allowing pairs formed of dispersing individuals from different colonies to rapidly bond and become fertile