ABSTRACT
In humans, a single amino acid change (V370A) in the Ecdysoplasin A receptor (Edar) gene is associated with a unique hair phenotype in East Asian populations. Transgenic experiments in mouse show that this mutation enhances Edar signaling in vitro, which in turn alters multiple aspects of hair morphology. Here we tested whether this substitution contributes to the spiny hair observed in six families of rodents. We first measured hair traits, focusing on guard hairs and their physical properties, such as tension and deformation, and compared the morphology between spiny and non-spiny sister lineages. Two distinct hair morphologies were repeatedly observed in spiny rodent lineages: hairs with a grooved cross-section and a second near cylindrical form, which differ in their cross-section shape as well as their tensiometric properties. Next, we sequenced a portion of the Edar locus in these same species. Most species surveyed have the common amino acid valine at position 370, but the kangaroo rat and spiny pocket mouse have an isoleucine. We also found one additional amino acid variant: tree rats have a Leu422Val polymorphism. However, none of these variants are associated with changes in hair morphology. Together these data suggest that the specific Edar mutation associated with variation in human hair morphology does not play a role in modifying hairs in wild rodents, highlighting that different evolutionary pathways can produce similar spiny hair morphology.