Intraspecific variation and functional study of VERL polymorphism in Pacific abalone (Haliotis discus hannai Ino) and giant abalone (H. gigantea Gmelin).

Sperm and eggs have interacting proteins on their surfaces that affect their compatibility during fertilization. These gamete recognition proteins (GRPs) are typically polymorphic within species, resulting in variations in gamete affinity. This study presents the full-length sequence of VERL, an egg vitelline envelope receptor for sperm lysin, in Pacific abalone (Haliotis discus hannai Ino) and giant abalone (Haliotis gigantea Gmelin). The full-length VERL cDNA sequence in Pacific abalone (11,373 bp) encodes 3790 amino acids, most of which are organized into 21 tandem repeats. In giant abalone, the VERL spans 9405 bp and encodes 3134 amino acids, including 17 tandem repeats. By resolving the nucleotide polymorphisms from resequencing data into haplotypes, high allelic diversity was found in VERL domain repeats 1-2 in both species. Further analysis of intraspecific variation in this region revealed that the alleles of VERL repeats 1-2 in Pacific abalone clustered into two clades, yet no significant divergence was observed among the three Pacific abalone geographic populations. In contrast, alleles in giant abalone were subdivided into two distinct branches, separated by a maximum of 12 amino acid substitutions. Notably, this study provides the first evidence of assortative mating between male and female gametes based on VERL genotypes in giant abalone. Overall, this study revealed the amino acid polymorphism of VERL in two abalone species and its functional effects on fertilization potential. These findings provide a foundation for future research on gamete recognition mechanisms and support selective breeding strategies to enhance abalone reproductive efficiency.