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Stabilizing Selection on Behavior and Morphology Masks Positive Selection on the Signal in a Salamander Pheromone Signaling Complex

Summary: Stabilizing Selection on Behavior and Morphology Masks Positive Selection
on the Signal in a Salamander Pheromone Signaling Complex
Richard A. Watts,* Catherine A. Palmer,* Richard C. Feldhoff, Pamela W. Feldhoff,
Lynne D. Houck,* Adam G. Jones, Michael E. Pfrender,§
Stephanie M. Rollmann,k and Stevan J. Arnold*
*Department of Zoology, Oregon State University, Corvallis; Department of Biochemistry, School of Medicine,
University of Louisville, Louisville, Kentucky; School of Biology, Georgia Institute of Technology, Atlanta;
§Department of Biology, Utah State University, Logan; and kDepartment of Zoology, North Carolina State University, Raleigh
Natural selection maintains the integration and coordination of sets of phenotypic characters that collectively perform
a task. In functional complexes in which characters span molecular to behavioral levels of organization, we might then
expect similar modes of selection to produce similar patterns in evolutionary divergence at each level. To test this
expectation, we diagnosed selection at behavioral, morphological, and molecular levels for courtship pheromone
signaling by plethodontid salamanders. At the levels of morphology and behavior tens of millions of years of stasis
(stabilizing selection) occur on each side of a transition from vaccination to olfactory delivery modes. As a proxy for the
molecular level, we used plethodontid receptivity factor (PRF), a protein that is an active component of the pheromone.
We cloned PRF from 12 Plethodon spp. spanning the delivery transition and obtained multiple alleles from each
individual surveyed. Analyses of 61 alleles for PRF identified elevated nonsynonymous over synonymous substitution
rates along lineages in a molecular phylogeny, and at 8% of sites in the protein, indicating that positive (directional)
selection has acted on this vertebrate pheromone gene. Structural models showed PRF is in a family of cytokines
characterized by a four­a-helix bundle. Positive selection in PRF was associated with receptor binding sites that are


Source: Arnold, Stevan J. - Department of Zoology, Oregon State University
Houck, Lynne D. - Department of Zoology, Oregon State University
Jones, Adam - Department of Biology, Texas A&M University
Pfrender, Michael - Department of Biological Sciences, University of Notre Dame


Collections: Biology and Medicine; Environmental Sciences and Ecology