Positive selection in the egg receptor for abalone sperm lysin

Area of Science:

• Evolutionary Biology
• Reproductive Biology
• Genetics

Background:

• Speciation is a central problem in evolutionary biology.
• Prezygotic reproductive isolation in free-spawning animals may arise from rapid divergence of sperm and egg binding proteins.
• Abalone sperm lysin evolves rapidly, but the egg receptor was thought to evolve neutrally.

Purpose of the Study:

• To investigate the evolutionary dynamics of the egg vitelline envelope receptor for lysin in abalone.
• To test theoretical models predicting rapid positive selection on both male and female reproductive proteins.
• To provide molecular evidence for the coevolutionary chase hypothesis in gamete recognition systems.

Main Methods:

• Comparative sequence analysis of the abalone egg vitelline envelope receptor for lysin.
• Phylogenetic analysis to detect positive Darwinian selection.
• Examination of sequence diversity at the amino-terminal end of the receptor.

Main Results:

• The amino-terminal end of the egg vitelline envelope receptor for lysin shows evidence of positive Darwinian selection.
• These findings contrast with previous neutral evolution findings for other parts of the receptor.
• Supports theoretical models of rapid coevolution between gamete recognition proteins.

Conclusions:

• The egg receptor for sperm lysin evolves under positive selection, consistent with a coevolutionary "chase" between sexes.
• This rapid coevolution of gamete recognition systems can drive speciation.
• Sexual selection, conflict, or pathogen avoidance may drive this evolutionary arms race.