Genome size varies considerably across the diversity of plant life. Although genome size is, by definition, affected by genetic presence/absence variants, which are ubiquitous in population sequencing studies, genome size is often treated as an intrinsic property of a species. Becher et al. studied intra- and interspecific genome size variation in taxonomically complex British eyebrights (Euphrasia, Orobanchaceae). Their aim was to document genome size diversity and investigate underlying evolutionary processes shaping variation between individuals, populations and species.
The team found considerable intraspecific genome size variation, and observed isolation-by-distance for genome size in outcrossing diploids. Tetraploid Euphrasia showed contrasting patterns, with genome size increasing with latitude in outcrossing Euphrasia arctica, but with little genome size variation in the highly selfing Euphrasia micrantha. Interspecific differences in genome size and the genomic proportions of repeat sequences were small.
Becher et al. show the utility of treating genome size as the outcome of polygenic variation. Like other types of genetic variation, such as single nucleotide polymorphisms, genome size variation may be affected by ongoing hybridization and the extent of population subdivision. In addition to selection on associated traits, genome size is predicted to be affected indirectly by selection due to pleiotropy of the underlying presence/absence variants.
Becher, H., Powell, R.F., Brown, M.R., Metherell, C., Pellicer, J., Leitch, I.J., Twyford, A.D., 2021. The nature of intraspecific and interspecific genome size variation in taxonomically complex eyebrights. Annals of Botany. https://doi.org/10.1093/aob/mcab102