Evolutionary genetics and genomics of flower colour loci in an Antirrhinum hybrid zone

Unravelling the genetic nature of reproductive isolation is crucial to understanding the maintenance of diversity between populations. In hybrid zones, loci that establish a barrier to gene flow between populations remain divergent, whereas neutral unlinked loci become mixed. In those instances, fit allelic combinations across several loci can be maintained through selection, but this is antagonized by gene flow and recombination. Here, I show that particular allelic combinations in a linked cluster of loci responsible for a flower colour polymorphism between two A. majus subspecies are maintained despite recombination in a hybrid zone. I reveal that a known locus that controls the magenta flower colour of the subspecies, ROSEA (ROS), is highly divergent between them, compared with most of the genome. The divergence region extends downstream of ROS, likely due to selection on another linked, but unidentified, locus that also controls flower colour, ELUTA (EL). Fine-mapping experiments identified an interval containing EL and regions within ROS that control different components of the magenta phenotype. Transcriptome analysis from flower buds suggests that MYB-like transcription factors within the mapped intervals control this trait. ROS and EL interact epistatically, meaning that the phenotype of an individual depends on the particular allelic combination it has for these loci. In the hybrid zone, markers in ROS and EL are in high linkage disequilibrium, but ~5% of recombinant haplotypes were found in the population. Recombinant haplotypes modify the phenotype of the flowers in relation to the parental subspecies, and therefore may be selected against. The data suggest that allelic combinations in ROS-EL are maintained by selection, despite gene flow and recombination between the two subspecies. This work reveals the consequences of selection, gene flow and recombination in shaping the patterns of genomic divergence in linked clusters of loci that establish an isolating barrier between populations.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2014

Author dc:creator

• Tavares, Hugo

Language dc:language

en