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

Abstract

Damaraland mole-rats Fukomys damarensis are eusocial subterranean rodentsthat exhibit an extreme reproductive skew with one female and one or two malesbreeding. The non-reproductive individuals in the colony are reproductivelysuppressed, 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 howthese individuals can quickly become sexually active if the causes of suppressionare removed. This study investigated circulating gonadotrophin concentrations[follicle stimulating hormone (FSH)] and testicular morphology and function inreproductive and non-reproductive male Damaraland mole-rats taken directlyfrom their natal colonies and non-reproductive males that had been introduced tonon-kin females outside their colony for 10 or 60 min. The main findings were that60-min exposure males had a significantly heavier body mass-corrected testicularmass than reproductive males. In addition, the external seminiferous tubulediameter was significantly larger in reproductive males than in non-reproductivemales, and the tubule lumen area was significantly greater in reproductive, 10 and60-min exposure males than in non-reproductive males. Plasma concentrations ofFSH were not different between the groups; however, the reproductive statussignificantly affected the area of testicular tissue stained immunopositive for theFSH receptor (FSH-R). Reproductive males had almost six times more FSH-Rcompared with non-reproductive males, and 60-min exposure males had eighttimes more FSH-R compared with non-reproductive males. In conclusion, theincrease in the seminiferous tubular lumen area and the testicular FSH receptorcontent when non-reproductive male mole-rats come into contact with non-kinfemales indicates a rapid activation of testicular spermatogenic pathways toaccompany the onset of copulatory behaviour, and is likely to be adaptive inallowing pairs formed of dispersing individuals from different colonies to rapidlybond and become fertile.