PARENT SESSION
MINISYMPOSIUM XIII. Pheromone Signaling and Reproductive Behavior.
11:00 AM-12:30 PM
Harborside D
Chair: Baum, Michael¹, ¹

(M39) RELAXATION OF SELECTIVE PRESSURE ON COMPONENTS OF A PHEROMONE SIGNALING PATHWAY DURING PRIMATE EVOLUTION.

Liman, Emily^1,2, Innan, Hideki¹, ¹ Department of Biological Sciences, Los Angeles, CA² Program in Neurosciences, Los Angeles, CA

ABSTRACT- The vomeronasal organ (VNO), which detects pheromones and other signaling molecules in many vertebrate species, has been thought to be vestigial in humans. In accordance with this idea, a key signaling component of VNO sensory transduction, the ion channel TRP2, is a pseudogene in humans. TRP2 is expressed exclusively in the VNO and is essential for VNO function in mice. Thus the accumulation of deleterious mutations within the coding sequence of TRP2 most likely reflects a relaxation of selective pressure on a functional VNO. To understand where in primate evolution a functioning VNO was lost, we determined the time at which mutations in the TRP2 gene occurred within primate phylogeny. Of six deleterious mutations in the TRP2 gene (2 frameshifts and 4 premature stop codons), the first arose after the split between Old World (OW) and New World (NW) monkeys, and before the radiation of OW monkeys from apes. By analyzing the rate of nucleotide substitutions that preserve the amino acid sequence (synonomous substitutions) versus the rate of nucleotide substitutions that change the amino acid sequence (nonsynonomous substitutions), we have been able to map through primate phylogeny the selective pressure on the TRP2 gene. Our data shows that there has been high purifying selective pressure on the TRP2 gene in rats, mice and a prosimian primate, the lemur, consistent with the known functional importance of the VNO in these species. Selective pressure was also high in the common ancestor of OW and NW monkeys, but then was relaxed independently in both lineages. We find no evidence for selective pressure on the gene in any extant species of OW monkey or ape, including humans. These data support the contention that the VNO is vestigial in humans, and point to a time in human evolution after the divergence of NW monkeys from OW monkeys and apes where selective pressure on components of VNO sensory transduction was relaxed. This corresponds to the time in human evolution where primates developed trichromatic color vision, suggesting that visual cues may have replaced chemical cues in signaling reproductive and social status.

KEY WORDS: vomeronasal, pheromone, evolution