Graduate Thesis Or Dissertation

 

Chemical signaling and pheromone evolution in plethodontid salamanders Public Deposited

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  • My dissertation focuses on the evolutionary forces that have shaped the chemical signaling system of plethodontid salamanders. Pheromones mediate two phases of plethodontid reproduction: mate attraction prior to courtship and female persuasion during courtship. Substrate-borne chemical signals are believed to play an important role in mate attraction for these animals. A behavioral assay of sex- and species-specific odor preferences in closely related species of Plethodon indicates that: (1) there is asymmetry on the receiver side of the system, wherein male salamanders invest more energy searching for mating partners than do females; (2) substrate-borne chemical signals are sexually dimorphic and male preference strongly favors the female odor versus the male odor; (3) females of allopatric salamander species have evolved distinctive chemical cues; and (4) female chemical signals of sympatric species are divergent and may play a role in sexual isolation. Sexual persuasion is another phase of plethodontid reproduction that is mediated by chemical signals. Plethodontid Receptivity Factor (PRF) is a proteinaceous pheromone that is produced by the male and delivered to the female during courtship. Female receptivity increases following application of this pheromone. PRF is a recent innovation of the male courtship signal, originating in eastern Plethodon (~27 MYA). Codon-substitution models indicate that several amino acid sites along the PRF protein have experienced positive selection. Structural modeling suggests that many of these selected residues are important for receptor binding. Adaptive change in this pheromone is likely driven via a coevolutionary association with female receptors. The male plethodontid courtship signal, however, is comprised of multiple chemical components. I investigate micro- and macro-evolutionary divergence in plethodontid chemical communication by surveying two additional pheromone component genes, PMF and SPL. Like PRF, regions of the PMF and SPL genes have experienced adaptive change. At least one of these components (SPL) has been retained in the signaling system for ~100 MY. However, significant differences in the composition of the courtship pheromone are evident in some plethodontid lineages. It appears as if at least two lineages (Desmognathus and eastern Plethodon) use different major pheromone components and yet achieve the same behavioral response in the female (increased receptivity).
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