Question

Describe two ways by which eggs and sperm ensure they are interacting with gametes of their same species. (this is for sea urchins specifically)

Answer 1

Chemotaxis-In many species of Mollusca, Echinodermata, and cnidaria it was observed that the male sperms are attracted to the female egg belonging to the same species via chemotaxis (secretion and formation of the chemical gradient by egg cell). Resact is a chemotactic molecule isolated from the egg of sea urchin it is around 14 amino acid long. Resact is highly diffusible in water. It is species specific and it does not attract the sperm of another species. Resact plays an important role in sperm activation and increases sperm motility as well as mitochondrial respiration.

The acrosomal reaction-The acrosomal reaction is activated When sperm of sea urchin comes in contact with the egg. The acrosomal vesicle of sperm is exocytosed due to contact with an egg . This leads to the release of proteolytic enzymes. The exocytosis is caused via Ca-mediated fusion of the acrosomal membrane of sperm with the plasma membrane of adjacent sperm. This reaction is very species-specific.