ホオジロムクドリ <i>Sturnus c. contra</i> のオスの生殖付属腺の年周期変化

The male sex accessories were studied from gravimetry, histology and biochemical standpoint during the annual testicular cycle and nesting cycle in a sub-tropical passerine bird, the Pied Myna (Sturnus contra contra). The findings revealed that all the sex accessories showed cubodial to low columnar, non-ciliated and non-secretory cells, with low seminal glomus weight and sialic acid content during the non-breeding phase (August to January). The epithelial cells were moderately enlarged with a moderate increase in seminal glomus weight and sialic acid concentration during the pre-breeding phase (February and March); greatly enlarged with differentiation of cells and secretory activity followed by a further increase in weight and of sialic levels of the seminal glomus during the breeding phase (April and May); and regressed with reverse changes in the seminal glomus during the post-breeding phase (June and July).<br>During the nesting cycle (i. e. the breeding phase) particularly the early nest-building period, the values of all the above parameters in the sex accessories increased. They were highest in the late nest-building period and decreased gradually in the egg-laying, incubation and nestling periods.<br>It is suggested that in the Pied Myna, sex accessory activity varies simultaneously with the annual gonadal cycle, being low during the non-breeding phase, at a moderately increased in the pre-breeding phase, at a maximum during breeding and declining thereafter. But during the nesting cycle sex accessory activity increased in the early nest-building period, attained a peak in the late nest-building period and declined gradually in the egg-laying, incubation and nestling periods. Changes in the sex accessories are considered to be the result of changes in ovarian steroid activity during the gonadal cycle of this bird.