The morphological characteristics and modification of the oviducal glands adapted for long-term sperm storage and fertilization in Amphioctopus fangsiao

Abstract

Sperm storage is an important reproductive strategy in Amphioctopus fangsiao. Sperm can be stored in the oviducal glands up to eight months before fertilization. However, studies on the underlying storage mechanisms remain limited. In this study, the morphological structures of the oviductal glands and the changes adapted for sperm storage and fertilization were investigated by Hematoxylin eosin (HE) staining, transmission electron microscopy (TEM), and Alcian blue periodic acid Schiff (AB-PAS) staining. Results revealed that the nucleo-cytoplasmic ratio of the peripheral gland cells decreased and the eosinophilic secretory granules (glycoproteins) appeared in the cytoplasm and lumen during sperm storage. The cytoplasm of the central gland appeared vacuolated and AB pH 2.5 (+) secretions (acid mucins) were dispersed in the cells. These secretions may pass through the central cavity into the oviducts and be involved in zygote packaging. The spermathecae are composed of columnar epithelial ciliated cells with secretory functions. PAS (+) glycoproteins were found in the lumen, providing a microenvironment conducive to sperm survival. Cilia in the oviducts, central cavity, and spermathecae may help with sperm delivery, storage, and release, and egg transport. This study enhances our understanding of the biological reproduction process in A. fangsiao.