Sperm Chemotaxis: The First Authentication Events Between Conspecific Gametes Before Fertilization

Abstract

Sperm chemotaxis toward eggs before fertilization has been observed in many living organisms. Sperm chemotaxis is the first communication or signaling event between male and female gametes in the process of fertilization, and species-specific events occur in many cases. Thus, sperm chemotaxis may act as a safety process for authenticating that fertilization occurs between conspecific egg and sperm and helps to prevent crossbreeding. Here, we introduce mechanisms of sperm chemotaxis, focusing on cross-talk between gametes and species specificity. Furthermore, we discuss the interactions between sperm-activating and sperm-attracting factors (SAAFs) in the ascidian species and that SAAF receptors on sperm cells are not all-or-none responses. The SAAF receptors may accept SAAFs of related species (closely related molecules), with different affinities.