Hybrid Zones

Many species are subdivided into a mosaic of genetically distinct populations, which are separated by narrow hybrid zones. By measuring the frequency of genotypes across such hybrid zones, we can estimate the rate of gene flow, the strength of selection etc. – quantities that would be very hard to measure directly.

We are studying the ecological and evolutionary dynamics of hybrid zones between two sub-species of Antirrhinum (snapdragons) with different flower colours (yellow and magenta – pictured). In this system, two major loci control flower colour, giving rise to six colour phenotypes across a narrow hybrid zone. This raises the question as to how the alleles that control the distinct phenotypes arise and spread despite strong barriers to invasion into parental populations. In collaboration with researchers in the UK (Enrico Coen’s group in Norwich) and Toulouse (Christophe Andalo and Monique Burrus) and Australia (David Field), we are using a range of ecological field work, population genetic and genomic approaches to gain a better understanding of how species diverge during the speciation process. Some of the projects we are working on in the group include: (1) reconstruction of a large-scale multi-generational pedigree to examine the fitness landscape for interacting alleles that control the colour space, (2) the topology of divergence and cline behaviour across the genome to determine how alleles arise and spread and what barriers exist to their dispersal, (3) the role of pollinator behaviour and frequency dependence in hybrid zone maintenance, (4) Self incompatibility and introgression of the genome, (5) Inbreeding depression and its role in maintaining self-incompatibility.

The dynamics of hybrid zones also apply to biocontrol programmes where the introduced agent only increases above a threshold.  Nick Barton is working with Michael Turelli to optimise a program to eliminate dengue fever and other diseases by releasing Wolbachia infected mosquitoes (EliminateDENGUE).

Recent Papers

TavaresH., WhibleyA., FieldD.L., BradleyD., Couchman, M., Copsey L.,BurrusM, Ellouet J, Andalo C, LiM, LiQ., XueY., RebochoA.B., BartonN.H., CoenE. 2018 Selection and gene flow shape genomic islands that control floral guides. PNAS 115:11006-11011.

Bod’ova, K., Priklopil, T., Field, D.L., Barton, N.H., Pickup, M. 2018. Evolutionary pathways for the generation of new self-incompatibility haplotypes in a non-self recognition system. Genetics 209: 861-883

Westram AM, Rafajlović, Chaube P, Faria R, Larsson T, Panova M, Ravinet M, Blomberg A, Mehlig B, Johannesson K, Butlin R (2018) Clines on the seashore: The genomic architecture underlying rapid divergence in the face of gene flow. Evolution Letters 2: 297–309.

Arathoon, L., Surendranadh, P., Barton, N.H., Field, D.L., Pickup, M., Baskett, C.A. 2020. Estimating inbreeding depression in a long-term study of snapdragons.  bioRxiv

A. majus spp. striatum (left), A. majus spp. pseudomajus (right) and their hybrids (middle)
Antirrhinum hybrid zone