Egg coats of the rock shrimp Rhynchocinetes typus: ultrastructural characterization and their function during fertilization

Scanning Electron Microscopy of Vitellogenic Oocytes and Spawned Eggs of the Portunid Crab Charybdis hellerii (Crustacea-Brachyura) (Milne Edwards, 1867)

Background:

The portunid crab Charybdis hellerii is an economically critical aquatic species in the Mediterranean region. Several investigators have reported scanning electron microscopy (SEM) observations on some crustacean's eggs' morphology. Going through the previous studies, knowledge regarding the morphology of C. hellerii. vitellogenic oocytes and spawned egg membranes are not available.

Aims and Objectives:

In the present study, an attempt has been made to describe the morphology and the structure of the membranes of vitellogenic oocytes and the newly spawned eggs to provide necessary information for further studies on the reproductive and evolutionary biology of the crab C. hellerii.

Materials and Methods:

Samples of ripe pinkish orange ovaries of non-ovigarous females and the spawned incubated eggs of ovigerous females with orange and grey spawns were processed for scanning electron microscopy. The prepared samples were examined in a Zeiss DSM 940 scanning electron microscope.

Results:

The present SEM study revealed that, vitellogenic oocytes are highly packed with yolk inclusions, which appear to be embedded in a definite acellular matrix and surrounded by a distinct chorion, which is pierced by several pores. The follicle cells appear polygonal in shape and interconnected through thin lateral projections and strongly associated with vitellogenic oocytes. The brooded fertilized eggs are attached through a marked stalk (funiculus) and surrounded by three distinct envelopes, which showed specific ornamentations and variations in their surface topography. The outer envelope coarsely wrinkled, while the middle envelope showed finely wrinkled ornamentation, and the inner envelope appeared with its characteristic spongy, porous appearance.

Conclusions:

This study denotes a significant difference between mature vitellogenic oocytes inside the ripe ovary and the spawned ova. The differences have been shown in the structure and external ornamentation of their surrounding membranes. Unlike the vitellogenic oocytes, the spawned ova were surrounded by three distinct layers, which are differ in their surface architecture. Such membrane architecture is species specific characteristic and has been thought to be an adaptive feature for brooded fertilized eggs to survive from stressful environmental conditions.

Role of vitelline envelope during fertilization in the black tiger shrimp, Penaeus monodon

Animal eggs possess investments through which sperm must penetrate. The aim of the present study was to investigate the role of the egg coating, the vitelline envelope, during sperm-egg interactions in the black tiger shrimp, Penaeus monodon. The site(s) of primary binding between sperm and egg and the possible binding molecule(s) for sperm were identified. In vitro adsorption of the vitelline envelope protein onto the sperm surface showed that primary binding occurred between the sperm anterior spike of acrosome intact sperm and the vitelline envelope. Results from streptavidin blotting revealed that the component of the vitelline envelope that interacts with the sperm integral membrane protein is a 370kDa protein. In addition, it was shown that the vitelline envelope protein had no ability to induce acrosome reaction. These results suggest that the function of the vitelline envelope is as a primary binding site for sperm in shrimp, but not a sole trigger for the acrosome reaction.