Abstract
The release and sensation of sex pheromone play a role in the reproductive success of vertebrates including fish. Previous studies have shown that the weather loach Misgurnus anguillicaudatus perceives sex pheromones by olfaction to stimulate courtship behavior. It was speculated that weather loaches use smell to recognize intraspecific mates. However, the identification of loach pheromone receptor has not been reported. By comparative transcriptomic approach, we found that the olfactory receptor gene or114-1 was male-biasedly expressed in the olfactory epithelium of M. anguillicaudatus, M. bipartitus and the closely related species Paramisgurnus dabryanus. This sex-biased expression pattern implicated that or114-1 presumably encoded a sex pheromone receptor in loaches. M. bipartitus and P. dabryanus, like zebrafish, possess one or114-1 only. However, in M. anguillicaudatus, or114-1 has two members: Ma_or114-1a and Ma_or114-1b. Ma_or114-1a, not Ma_or114-1b, showed sex-differential expression in olfactory epithelium. Ma_or114-1b has base insertions that delayed the stop codon, causing the protein sequence length to be extended by 8 amino acids. Ma_or114-1a was subject to positive selection resulting in adaptive amino acid substitutions, which indicated that its ligand binding specificity has probably changed. This adaptive evolution might be driven by the combined effects of sexual selection and reinforcement of premating isolation between the sympatric loach species.
Highlights
The sensory system and its signal source play an important role in the pre-mating reproductive isolation between species [1,2]
In the sex-differentially expressed gene sets preliminarily identified by the bioinformatic analysis on the transcriptomic data of olfactory epithelium, one olfactory receptor gene was found showing male-biased expression in all the three loach species
After checking the gene annotations, we found that this gene was orthologous to zebrafish or114-1 which has been functionally verified as a sex pheromone receptor [18]
Summary
The sensory system and its signal source play an important role in the pre-mating reproductive isolation between species [1,2]. Similar to the visual system and its signals, the chemical sensory system (including smell and taste) and chemical signals participate in the evolution of genetic communication barriers [1,3]. Pheromone is a chemical signal, a molecule or a fixed combination of molecules, released by the organism to stimulate the instinctive response of other individuals within the same species, and it is widely present in various groups in the animal kingdom [4]. In the past 10 years, sex pheromones have been identified in many species, including fish, with their extremely diverse chemical properties
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