Molecular Variation in the Agouti Gene in Pocket Mice from the Carrizozo Malpaís Lava Flow

Abstract

Color variation in pocket mice, Chaetodipus intermedius, presents a unique opportunity to study genes contributing to convergent adaptation. While pocket mice generally have light coats matching sand-colored rocks on which they live, dark mice are found on basalt lava flows in the desert southwest. Because the mice match their habitat, they are less likely to be recognized by visual hunters. In one lava flow population, the genetic basis of melanism was identified in the melanocortin-1 receptor (Mc1r). However, it is known that the underlying locus is different in a lava flow population in Carrizozo, NM. In a backcross, it was demonstrated that melanism in Carrizozo is recessive and associated with a marker in agouti, a locus encoding an MC1R antagonist. However, because of the low level of recombination in this cross, genes linked to this marker could underlie color variation. Here, I sequenced regions of agouti previously uncharacterized in pocket mice. I genotyped Carrizozo mice in these regions and identified a SNP significantly associated with coat color likely linked to a causative mutation within agouti. These data support the hypothesis that melanism has arisen at least twice in pocket mice due to changes in different pigmentation genes, Mc1r and agouti.