Seasonal reproductive activity of male formosan wood mice (Apodemus semotus): Relationships to androgen levels

The annual reproductive cycle of adult male Formosan wood mice (Apodemus se motus) collected monthly from the Alishan area, Taiwan, was investigated. M ean monthly body mass varied between 25.0 g +/- 0.8 SE and 27.1 +/- 1.3 g a nd did not show significant seasonal change. Mass of reproductive organs, s permatogenic activity, and levels of testicular and plasma androgen exhibit ed a distinct pattern of seasonal change. Testes, epididymides, and seminal vesicles were lightest and spermatogenesis was virtually arrested in Janua ry and December. For the remainder of year, all animals examined were sperm atogenically active. However, spermatogenic activity was most intense and r eproductive organs were heaviest in March-April and August-September. A dec line occurred in mass of reproductive organs and diameter of seminiferous t ubules in May-July, but spermatogenesis was unaffected qualitatively. Level s of testicular and plasma androgen were elevated in March-April and August -September, coinciding with periods of intense spermatogenic activity and t he heaviest reproductive organs and were significantly correlated with mass of testes, epididymides, and seminal vesicles, and diameter of seminiferou s tubules. Day length and temperature, but not precipitation, were correlat ed with mass of testes, epididymides, and seminal vesicles. This is the Ist study to investigate seasonal patterns of androgen levels in plasma and te stes in the genus Apodemus.