Untangling the hedge: Genetic diversity in clonally and sexually transmitted genomes of European wild roses, Rosa L.

Abstract

While European wild roses are abundant and widely distributed, their morphological taxonomy is complicated and ambiguous. In particular, the polyploid Rosa section Caninae (dogroses) is characterised by its unusual meiosis, causing simultaneous clonal and sexual transmission of sub-genomes. This hemisexual reproduction, which often co-occurs with vegetative reproduction, defies the standard definition of species boundaries. We analysed seven highly polymorphic microsatellite loci, scored for over 2 600 Rosa samples of differing ploidy, collected across Europe within three independent research projects. Based on their morphology, these samples had been identified as belonging to 21 dogrose and five other native rose species. We quantified the degree of clonality within species and at individual sampling sites. We then compared the genetic structure within our data to current rose morpho-systematics and searched for hemisexually co-inherited sets of alleles at individual loci. We found considerably fewer copies of identical multi-locus genotypes in dogroses than in roses with regular meiosis, with some variation recorded among species. While clonality showed no detectable geographic pattern, some genotypes appeared to be more widespread. Microsatellite data confirmed the current classification of subsections, but they did not support most of the generally accepted dogrose microspecies. Under canina meiosis, we found co-inherited sets of alleles as expected, but could not distinguish between sexually and clonally inherited sub-genomes, with only some of the detected allele combinations being lineage-specific.