Seasonal variations in the morphology of the seminal vesicles of the African straw-coloured fruit bat (Eidolon helvum)

The study investigated seasonal changes in the morphology of the seminal vesicles of Eidolon helvum in a typical African tropical environment. Seminal vesicles of forty-eight bats were examined during the early rainy, late rainy and peak dry seasons, using gross anatomical, histological and ultrastructural techniques. The interlobular connective tissue septa from the external capsule demarcated the glandular parenchyma into numerous lobules of tubulo-alveolar glands. A simple cuboidal epithelium of mono- or bi-nucleated cuboidal cells lined the glandular mucosa during the rainy season. This was replaced by a bistratified cuboidal epithelium, whose upper layer of cells showed evidence of degeneration, during the dry season. The PAS-positive secretory products appeared to be numerous during the rainy season, but few and clumped together during the dry season. The mean gross weight, interlobular septal thickness, acini diameter and epithelial height of the glands varied significantly with season. Ultrastructural features of the secretory cells during the rainy season showed well-developed cytoplasmic organelles, numerous electron lucid secretory vesicles and electron-dense granules. Secretory epithelial cells of the seminal vesicles are very active during the rainy season, while regeneration of degenerated epithelium in preparation for the next reproductive cycle occurs during the dry season.