Sperm competition influences sperm quality and seminal plasma protein expression among territorial males of the courtship cichlid

Sperm competition drives the plasticity of sperm quality and seminal fluid. However, how environmental and behavioral factors influence sperm competition and its outcome on the plasticity of sperm quality are unknown. In this study, we show males can asses the sperm competition level, and their fertilization-promoting sperm traits changes according to intensity. The promiscuous Tanganyikan cichlids Ophthalmotilapia ventralis perform their fertilization in the female mouth cavity. Sperm competition occurs in the female mouth as sperm is collected from multiple males. Behavioral (i.e., courtship success rates [CSR]) and environmental (density of spawning sites [DS]) factors are related to sperm collection. Seminal plasma glycoprotein 120 (SPP120) aids in sperm immobilization and aggregation, and sperm quality (longevity and velocity) could increase the probability of siring offspring. Based on an assumption of the involvement of DS and CSR on sperm collection, DS and CSR could influence the expression of SPP120 and sperm quality. We examined how sperm quality and SPP120 affect sperm competition-associated CSR and DS. Sperm longevity and velocity were positively correlated with DS. SPP120 expression was also positively correlated with CSR and DS. The plasticity of sperm quality and amount of SPP120 result in high fertilization competency according to sperm competition level.