Seasonal effects of photoperiod and temperature on spermatogenesis and male secondary sexual characters in the three-spined stickleback, Gasterosteus aculeatus L.

Abstract

Effects of photoperiod (16 h light (L): 8 h dark (D) and 8 h L: 16 h D) and temperature (18 and 8 °C) on spermatogenesis and androgen-dependent kidney hypertrophy in the three-spined stickleback were studied in alternate months of the year. In winter 16 h L: 8 h D in combination with 18 °C stimulated secondary sexual characters, whereas in spring other regimes were also stimulatory. Spermatogenesis was more active and the kidney more suppressed in 8 h L: 16 h D at 18 °C than in other groups in winter. In the natural annual cycle spermatogenesis is quiescent from the beginning of winter until the end of the breeding season in summer. Decline of secondary sexual characters in July is accelerated by high temperature. High kidney epithelium is never found together with vigorous spermatogenesis, indicating androgen-inhibition as a major factor in the control of spermatogenetic activity.