The nature of intraspecific and interspecific genome size variation in taxonomically complex eyebrights

Hannes Becher, Robyn F Powell, Max R Brown, Chris Metherell, Jaume Pellicer, Ilia J Leitch, Alex D Twyford

Research output: Contribution to journalArticlepeer-review


Background and aims
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. Here, we studied intra- and interspecific genome size variation in taxonomically complex British eyebrights (Euphrasia, Orobanchaceae). Our aim is to document genome size diversity and investigate underlying evolutionary processes shaping variation between individuals, populations and species.

We generated genome size data for 192 individuals of diploid and tetraploid Euphrasia and analysed genome size variation in relation to ploidy, taxonomy, population affiliation, and geography. We further compared the genomic repeat content of 30 samples.

Key results
We 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.

We 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 hybridisation 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.
Original languageEnglish
Article numbermcab102
Pages (from-to)639-651
Number of pages13
JournalAnnals of Botany
Issue number5
Early online date28 Jul 2021
Publication statusPublished - 8 Oct 2021


  • genome size
  • polygenic trait
  • euphrasia
  • ploidy
  • intraspecific variation
  • selection
  • pleiotropy
  • genomic repeats


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