Genetic Inference From Directional Asymmetry During Convergent Hindlimb Reduction in Squamates

Many threespine stickleback populations have independently evolved pelvic reduction, often due to independent mutations causing reduced Pitx1 expression. Notably, hindlimb reduction based on reduced Pitx1 expression produces left-larger directional asymmetry in the vestiges. Using this phenotypic signature, we tested for hindlimb directional asymmetry in six genera of squamate reptiles that have independently evolved some level of hindlimb reduction. Significant left-larger asymmetry occurred in one taxon, suggesting modification of Pitx1 expression. However, there was either no directional asymmetry or right-larger asymmetry in the remaining taxa, suggesting multiple developmental genetic pathways to hindlimb reduction in squamates and the vertebrates more generally