Background: The spiny mouse (Acomys cahirinus) is a desert-adapted rodent from the Middle East. We’ve recently described a menstrual cycle in this species. There is little knowledge of the structure and functional development of the male reproductive tract of Acomys cahirinus. The aim of our study was to characterise the structure and development of the male gonads and accessory organs at various stages of life and to relate these to testosterone concentration and capacity for sperm production.
Method: Male spiny mice were humanely euthanised at pre-pubertal (21d), post-pubertal (50d), adult (100d, 200d, 300d) and older adult (450d, 850d) ages and weighed. The reproductive tract was dissected into individual organs and accessory glands: testes, epididymides, seminal vesicles, prostate and penis. Each organ was weighed and processed to paraffin wax for histological analysis. Testes were homogenised and round spermatids were counted using a haemocytometer to calculate daily sperm production (DSP). Plasma testosterone concentrations were determined by radioimmunoassay.
Results: Acomys cahirinus has a baculum (penis bone). Circulating testosterone concentrations were highest in early adulthood (200d) correlating with the greatest penis weight 0.115±0.025g (mean±SEM). Post-pubertal sperm production was relatively consistent with age: DSP(d50)=1.3±0.20x107; DSP(d100)=2±0.20x107; DSP(d450)=2±0.17x107; DSP(d850)=1.7±0.5x107. Post-pubertal sperm motility remained high to at least 3 years of age. Seminiferous tubule diameter increased during puberty, but remained stable from adulthood (d100) to old age (d850). Organ and accessory gland weight correlated with age. Spiny mice have asymmetrical testes, with the left testis significantly heavier than the right throughout life (p<0.05).
Discussion: This is the first report of a baculum in the spiny mouse. Testosterone concentrations and relatively high rate of sperm production indicate high fecundity in this species to at least 3 years of age. The anatomy of the male reproductive tract in the spiny mouse is comparable to other rodents.