Abstracts (first author)
Selection on flower colour genes in a snapdragron hybrid zone
A major goal of evolutionary biology is to understand how diverging populations become distinct species. Although much progress has been made in identifying genes that contribute towards population divergence and speciation, direct measurements of their effect on fitness in nature are often difficult to obtain. We are studying the evolutionary dynamics of speciation between two subspecies of Antirrhinum (snapdragons) with different flower colours (yellow and magenta). In this system, two major loci control flower colour and give rise to six colour phenotypes across a narrow hybrid zone. Surprisingly, these species are visited by the same array of pollinators (large bees). This raises the question of how these genes initially arose and spread and how populations are currently maintained in the face of gene flow. To better understand the role of flower colour genes in speciation we are using an integrated approach to examine the role of selection, epistasis, drift and gene flow over multiple time scales. To examine short and long-term evolutionary processes we are using SSR and SNP markers for individuals sampled across the hybrid zone as well as sequence variation with Restriction-Associated DNA sequencing (RAD) data from allopatric populations. The existence of a steep cline (~280m wide) for flower colour and diagnostic markers linked to the underlying genes, suggests selection is acting against some of the hybrid colour phenotypes. Significant heterozygote deficit at small spatial scales (<30m) and an excess of parental phenotypes also suggests assortative mating may play a role in maintaining the hybrid zone. Initial results from RAD tags indicate that the highest regions of divergence (Fst) between allopatric populations are located near the genes that control flower colour. Taken together, these results suggest that selection is acting on the flower colour genes, likely through pollinators discriminating among the flower colour phenotypes within the hybrid zone.