Histological and morphometric analyses of seasonal testicular variations in the Jungle Crow (Corvus macrorhynchos)

A histological and morphometric study was conducted to examine the seasonal testicular variations in the Jungle Crow (Corvus macrorhynchos) of the Kanto area, Japan, from January to July. The paired testes mass, diameter and number of germ cells of the seminiferous tubules, and proportion of seminiferous tubule area and interstitium were examined. Hematoxylin and eosin-stained testis sections and ImageJ Software were used. Paired testes weight was found to increase by 55-fold from January to late March–early May, thereafter declining by 18-fold by June–July. Seminiferous tubule diameter increased fivefold from January to late March–early May, followed a fourfold decrease in June–July. The increase in testes weight correlated well with the increase in the diameter of the seminiferous tubule. In January, the seminiferous tubules constituted 56% of the testicular tissue and the interstitium 44%. During late March–early May, there was very little testicular interstitium (7.9%), and the seminiferous tubules were significantly enlarged (P < 0.05) (92%); this was followed by a gradual increase in the interstitial regression of testes. In January, the seminiferous epithelium contained a single layer of spermatogonia and Sertoli cells. The number of spermatogonia, primary and secondary spermatocytes, spermatids, and maturing spermatozoa were significantly increased (P < 0.05) in late March–early May, followed by regression from mid May. Our results indicate that the Jungle Crow has a non-breeding season in January, a pre-breeding season during February–mid March, a main breeding season during late March–early May, a transition period during mid May–late May, and a post-breeding season beginning in June.