How do populations diverge to create distinct species? Several interwoven processes are thought to underlie this speciation process: phenotypic divergence, ecological specialization and the formation of reproductive barriers. The formation of barriers is particularly problematic (causing Darwin to lose sleep) because it requires the spread of alleles that can reduce fitness. With the advent of population genomics and transcriptomics, combined with genetics and ecology, it is now possible to cast fresh light on these issues. We have used this approach to analyse diversification among Antirrhinum (snapdragon) species, which occupy non-overlapping regions of Southern Europe, but can form fertile hybrids when intercrossed and raised in the laboratory. Nevertheless, reproductive barriers between these species exist in the wild, evidenced by regions of the genome which show high divergence (genomic islands), and which form steep clines at hybrid zones where species come into contact. The question is how these genomic islands or barrier alleles arose. We hypothesise that their origin lies in changes in growth habit as ancestral populations spread into new environments (e.g from cliffs to slopes).
The aim of this project is to test this and other hypotheses using a combination of bioinformatics, population genomics, functional analysis and field work. The student will analyse genome sequences from a range of wild Antirrhinum species and determine signatures and evolutionary histories for barrier loci, using flower colour genes as exemplars. F2s of interspecific crosses will be analysed to determine the role of colour and growth habit genes in controlling phenotypic differences. The student will also perform field work to determine whether flower colour pattern and growth habit interact to influence pollinator choice or flower entry. Taken together, the above approaches should provide fresh insights into the origin of reproductive barriers and interplay between pattern and growth habit in the evolution of diversity.
Bradley, D., Xu, P., Mohorianu, I., Whibley, A., Field, D., Tavares, H., Couchman, M., Copsey, L., Carpenter, R., Li, M., Li, Q., Xue, Y., Dalmay, T.*, Coen, E.* (2017) Evolution of flower color pattern through selection on regulatory small RNAs Science 358, 925–928. * co-corresponding authors.
Tavares, H., Whibley, A., Field, D.L., Bradley, D., Couchman, M., Copsey, L., Elleoueta, J., Burrus, M., Andalo, C., Lie, M., Lie, Q., Xue, Y., Rebocho, A.B., Barton, N.H.*, Coen, E* (2018) Selection and gene flow shape genomic islands that control floral guides PNAS 115, 11006-11011. *co-corresponding authors.
Whitewoods, C. D., B. Goncalves, J. Cheng, M. Cui, R. Kennaway, K. Lee, C. Bushell, M. Yu, C. Piao, E. Coen (2020). Evolution of carnivorous traps from planar leaves through simple shifts in gene expression. Science 367 91-96. Awarded front cover.