Multiple genetic routes to pelvic spine loss in brook stickleback

Mykaela Tucker , Jon Mee, Sam Yeaman, Colton Arthurs

Pelvic spine loss has evolved repeatedly in stickleback species and represents an intriguing opportunity to study genetically parallel adaptation. While previous work has identified key loci associated with this trait, the extent to which different populations rely on the same genetic mechanisms remains unclear. The genetic basis of pelvic spine loss in Culaea inconstans (Kirtland 1840) has only been investigated in three populations. In two of these populations, the trait is associated with a mutation in lmbr1. In the third population, the trait is associated with a mutation in tbx4. In this study, we investigated the genetic basis of pelvic spine loss across seven additional populations. We used Sanger sequencing to identify if either previously described mutation in lmbr1 or tbx4 was present and associated with the trait in these populations. A mutation in lmbr1 was found to be associated in two populations, while a mutation in tbx4 was found to be associated in one population. Four populations showed no evidence that either lmbr1 or tbx4 was associated with pelvic spine loss, potentially implicating alternative mutations. These findings highlight the complexity of the evolutionary processes underlying repeated adaptation, including the extent of non-parallelism in the genetic basis of adaptive traits.