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An ancient pheromonal signal is found in aquatic courting salamandrids and terrestrial courting plethodontids, two highly divergent salamander families. In the aquatic courting salamandrids Cynops pyrrhogaster and C. ensicauda, the decapeptide sodefrin is cleaved from a larger 189 amino acid Sodefrin Precursor Factor (SPF) protein and released from a gland in the male’s cloaca during courtship. This decapeptide is capable of attracting females in a species-specific manner. In contrast, males of some terrestrial courting plethodontids apply uncleaved SPF directly to females to increase receptivity during courtship. In this study, we examine the presence, diversification, and evolution of this pheromone in two aquatic courting North American salamandrids, Notophthalmus viridescens and Taricha granulosa. We used degenerate primers, RT-PCR procedures, and cDNA obtained from sexually active males, in addition to genomic PCR methods. SPF was found to be expressed in abdominal gland region cDNA by males of both species and was additionally expressed in hedonic (genial) gland tissue of N. viridescens males. With respect to the presence of a cleaved pheromone product in these species, multiple alignments with C. pyrrhogaster sequences demonstrated a high degree of variability in the putative
decapeptide region. Cleavage sites were not identifiable. Site-specific tests reveal that positive selection has driven rapid evolutionary change at sites within N. viridescens and C. pyrrhogaster precursor proteins but not within T. granulosa. |
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