Nonapeptide receptor evolution in Tanganyika cichlids shows positive selection in VTR2A

Oxytocin (OT) and vasotocin (VT) are crucial nonapeptides regulating vertebrate physiology, including osmoregulation, reproduction, and social behavior. While their core functions are known, the precise evolutionary mechanisms driving their adaptation and receptor diversification, especially in rapidly evolving lineages like cichlids, are not fully understood. Gene duplications have expanded receptor families, but specific sites under selection remain elusive, hindering a complete picture of their adaptive roles.

Researchers analyzed the molecular evolution of nonapeptide receptors, including OTR and VTR families, in Tanganyika cichlids, a diverse group known for adaptive radiation. The study likely involved comparative genomic or transcriptomic analysis of receptor sequences to identify specific amino acid sites under selective pressure. The focus was on understanding how these receptors adapted during the cichlids' rapid diversification and the acquisition of new functions.

Analysis of nonapeptide receptors in Tanganyika cichlids revealed that most receptor sites are under strong purifying selection, indicating evolutionary conservation of core functions. However, specific sites, particularly within the extended intracellular loop 3 (IL3) of VTR2A receptors, exhibited clear signatures of positive selection. This suggests adaptive evolution at these key regulatory regions. Furthermore, the study identified that a specific amino acid within the VTR2Aa receptor subtype showed a direct correlation with pair-bonding behavior in these cichlids. These findings highlight the role of targeted molecular evolution in shaping complex social behaviors.