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Lineage-Specific Differences in Evolutionary Mode in a Salamander Courtship Pheromone

Summary: Lineage-Specific Differences in Evolutionary Mode in
a Salamander Courtship Pheromone
Catherine A. Palmer,*Richard A. Watts,* Ron G. Gregg, Maureen A. McCall,ā Lynne D. Houck,*
Richard Highton,§ and Stevan J. Arnold*
*Department of Zoology, Oregon State University; Department of Biochemistry and Molecular Biology, School of Medicine,
University of Louisville; āDepartment of Psychological and Brain Sciences, University of Louisville; and
§Department of Biology, University of Maryland
Functionally equivalent genes may evolve heterogeneously across closely related taxa as a consequence of lineage-specific
selective pressures. Such disparate evolutionary modes are especially prevalent in genes that encode postcopulatory re-
productive proteins, presumably as a result of sexual selection. We might therefore expect genes that mediate reproduction
prior to insemination to evolve in a similar manner. Plethodontid receptivity factor (PRF), a proteinaceous salamander
pheromone produced by the male, increases female receptivity during courtship interactions. To test for lineage-specific
differences in PRF's evolution, we intensively sampled PRF genes across the eastern Plethodon phylogeny (27 spp.; 34
populations) to compare gene diversification, rates of evolution, modes of selection, and types of amino acid substitution.
Our analyses indicate that PRF evolutionary dynamics vary considerably from lineage to lineage. Underlying this het-
erogeneity, however, are two well-defined transitions in evolutionary mode. The first mode is representative of a typical
protein profile, wherein neutral divergence and purifying selection are the dominant features. The second mode is char-
acterized by incessant, cyclical evolution driven by positive selection. In this mode, the positively selected sites are bound
by a limited assortment of acceptable amino acids that appear to evolve independently of other sites, resulting in a tre-
mendous number of unique PRF alleles. Several of these selected sites are implicated in receptor binding. These sites are


Source: Arnold, Stevan J. - Department of Zoology, Oregon State University


Collections: Biology and Medicine; Environmental Sciences and Ecology