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). / Graduation date: 2005
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29914 |
| Date | 28 May 2004 |
| Creators | Palmer, Catherine Anne |
| Contributors | Houck, Lynne D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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