Abstract
Fertilization (gamete fusion followed by zygote formation) is a multistage process. Each stage is mediated by ligand-receptor recognition of gamete interaction molecules. This recognition includes the movement of sperm in the gradient of egg chemoattractants, destruction of the egg envelope by acrosomal proteins, etc. Gametic incompatibility is one of the mechanisms of reproductive isolation. It is based on species-specific molecular interactions that prevent heterospecific fertilization. Although gametic incompatibility may occur in any sexually reproducing organism, it has been studied only in a few model species. Gamete interactions in different taxa involve generally similar processes, but they often employ non-homologous molecules. Gamete recognition proteins evolve rapidly, like immunity proteins, and include many taxon-specific families. In fact, recently appeared proteins particularly contribute to reproductive isolation via gametic incompatibility. Thus, we can assume a multiple, independent origin of this type of reproductive isolation throughout animal evolution. Gametic incompatibility can be achieved at any fertilization stage and entails different consequences at different taxonomic levels and ranges, from complete incompatibility between closely related species to partial incompatibility between distantly related taxa.
Highlights
The modern interpretation of species identity is based on the idea of unity of the species gene pool [1,2,3]
In different sea urchin species, the size of mature bindin ranges from 193 to 418 amino acids. It consists of a 55-amino-acid-conserved core, which is involved in gamete fusion, and two flanking regions responsible for species-specific adhesion to the egg envelope [13]
We have found only one published experimental confirmation that Gametic incompatibility (GI) and reinforcement are linked
Summary
The modern interpretation of species identity is based on the idea of unity of the species gene pool [1,2,3]. RI is realized via prezygotic and postzygotic mechanisms that are triggered at the stages that precede and follow zygote formation, respectively [3] Their biological roles differ: the prezygotic and reproductive barriers form and function at early stages of speciation; postzygotic – at the late stages [4,5,6,7]. It took at least 22 million years of divergence for the postzygotic RI between closely related bird species to form [3]. It is considered that as few as 10 amino acid changes in the sea urchins acrosomal protein bindin can lead to RI between two species
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