Abstract
Ostariophysans are the most diverse group of freshwater fishes and feature a pheromone-elicited fright reaction. However, the genetic basis of fright reaction is unclear. Here, we compared vomeronasal type 2 receptor-like (OlfC) genes from fishes having and lacking fright reaction, to provide insight into evolution of pheromonal olfaction in fishes. We found OlfC genes expanded remarkably in ostariophysans having fright reaction compared with fishes lacking fright reaction. Phylogenetic analysis indicates OlfC subfamily 9 expanded specifically in ostariophysans having fright reaction. Principle component and phylogenetic logistic regression analysis partitioned fishes by ecotype (having or lacking fright reaction) and identified OlfC subfamily 9 as being an important factor for fright reaction. Expression levels of expanded OlfC subfamily genes after fright reaction in zebrafish changed more than did genes that had not expanded. Furthermore, evidence of positive selection was found in the expanded OlfC proteins in ostariophysan fishes having fright reaction. These results provide new insight into the genetic basis of fright reaction in ostariophysan fish and will enable future research into the mechanism of action of OlfC proteins.
Highlights
Ostariophysans are the most diverse group of freshwater fishes and feature a pheromoneelicited fright reaction
Previous studies have suggested that the common ancestor of the ostariophysan fishes entered freshwater about 251 million years ago, which coincides with the global decrease in oxygen levels in marine waters caused by the large mass extinction event that occurred at the end of the Permian era[4]
The main olfactory epithelium mainly detects volatile odorants while the vomeronasal organ detects pheromones[15,16], there is some functional overlap between the main olfactory epithelium and the vomeronasal organ[17,18,19,20,21]
Summary
Ostariophysans are the most diverse group of freshwater fishes and feature a pheromoneelicited fright reaction. We compared vomeronasal type 2 receptor-like (OlfC) genes from fishes having and lacking fright reaction, to provide insight into evolution of pheromonal olfaction in fishes. We found OlfC genes expanded remarkably in ostariophysans having fright reaction compared with fishes lacking fright reaction. Phylogenetic analysis indicates OlfC subfamily 9 expanded in ostariophysans having fright reaction. Evidence of positive selection was found in the expanded OlfC proteins in ostariophysan fishes having fright reaction. These results provide new insight into the genetic basis of fright reaction in ostariophysan fish and will enable future research into the mechanism of action of OlfC proteins. The main olfactory epithelium mainly detects volatile odorants while the vomeronasal organ detects pheromones[15,16], there is some functional overlap between the main olfactory epithelium and the vomeronasal organ[17,18,19,20,21]
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