Duplication and Selection on Abalone Sperm Lysin in an Allopatric Population

While gene duplication is a major source of evolutionary novelty, the importance of this process in reproductive protein evolution has not been widely investigated. Here, we report the first known case of gene duplication of abalone sperm lysin in an allopatric subspecies found in the Eastern Atlantic, Haliotis tuberculata coccinea. Mass spectrometry identified both copies of the lysin protein in testis tissue, and 3-dimensional structural modeling suggests that both proteins remain functional. We also detected positive selection acting on both paralogs after duplication and found evidence of a recent selective sweep. Because H. t. coccinea occurs in geographic isolation from other abalone species, these findings suggest that the evolution of lysin is not driven to create reproductive barriers to unfit hybrid formation with an overlapping species. Instead, sexual selection or sexual conflict acting during abalone fertilization could be responsible for the recent positive selection on this protein. The presence of multiple, rapidly evolving lysin genes in H. tuberculata presents an opportunity to study the early stages of diversification of a protein whose function is well understood.