Ecological speciation in sympatric palms: 1. Gene expression, selection and pleiotropy

Ecological speciation requires divergent selection, reproductive isolation, and a genetic mechanism to link the two. We examined the role of gene expression and coding sequence evolution in this process using two species of Howea palms that have diverged sympatrically on Lord Howe Island, Australia. These palms are associated with distinct soil types and have displaced flowering times, representing an ideal candidate for ecological speciation. We generated large amounts of RNA-Seq data from multiple individuals and tissue types collected on the island from each of the two species. We found that differentially expressed loci as well as those with divergent coding sequences between Howea species were associated with known ecological and phenotypic differences, including response to salinity, drought, pH and flowering time. We identified loci with potential dual function in flowering time and soil adaptation, which effect on flowering time was validated by knocking orthologous genes in a model plant species. These results indicate that pleiotropy could have favoured the evolution of barrier traits in this system, despite ongoing gene flow