DNA Ploidy Variation and Population Structure of the Morphologically Variable Helichrysum odoratissimum (L.) Sweet (Asteraceae) in South Africa
Abstract
Premise of research. Plant diversification can be a result of many different factors, such as environment or genome size variation.
Further, the presence of phenotypic or genomic variation could highlight the presence of a cryptic lineage. Here, we tested whether phenotypic and genomic differences support the presence of a cryptic lineage in the South African populations of Helichrysum odoratissimum (L.) Sweet.
Methodology. We used estimates of genetic structure from microsatellite data and cytogenetic data from 17 sampled populations, paired with morphological measurements from representative populations, to test for the presence of cryptic lineages.
Pivotal results. Ploidy level estimates for the populations that span the species' South African distribution indicated that 15 of the 17 populations contain either putative DNA-diploid or DNA-hexaploid individuals and that two populations contain both putative DNA-diploids and DNA-hexaploids.
Population genetic analyses of seven microsatellite loci showed reduced admixture (gene flow) between populations of different ploidies, as well as across three geographic regions (Mpumalanga, the Drakensberg, and the Western Cape). We found leaf size differences between plants of different ploidy; plants with larger genome sizes exhibit longer and wider leaves than plants with smaller genome sizes.
Conclusions. While the role of polyploidy in global floral diversification is well accepted, the extent to which polyploidy contributes to specific diverse regions, such as South Africa, is less well known.
Our results suggest that morphologically variable populations of H. odoratissimum are distributed across distinct geographic regions in South Africa that coincide with different genome sizes. The Knsyna area of the Western Cape harbors a center of genomic diversity, as well as a cryptic hexaploid subspecies, possibly due to the variability in rainfall patterns, as summer rainfall changes over to winter rainfall in this region.
This study contributes to the emerging work surrounding the microhabitat differences of ploidies within the context of establishment and subsequent divergence.