Genetic diversity and conservation status of Helianthus verticillatus, an endangered sunflower of the southern United States

Authors: EDWARDS, TYLER - University Of Tennessee; TRIGIANO, ROBERT - University Of Tennessee; OWNLEY, BONNIE - University Of Tennessee; WINDHAM, ALAN - University Of Tennessee; WYMAN, CHRISTOPHER - University Of Tennessee; Wadl, Phillip; HADZIABDIC, DENITA - University Of Tennessee

Submitted to: Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2020
Publication Date: 5/15/2020
Citation: Edwards, T.P., Trigiano, R.N., Ownley, B.O., Windham, A.S., Wyman, C.R., Wadl, P.A., Hadziabdic, D. 2020. Conservation efforts of Helianthus verticillatus: Fine scale genetic characterization of this rare species. Heredity. 11:410. https://doi.org/10.3389/fgene.2020.00410.
DOI: https://doi.org/10.3389/fgene.2020.00410

Interpretive Summary: Helianthus verticillatus, commonly known as the whorled sunflower, is a herbaceous perennial endemic to four locations in Alabama, Georgia, and Tennessee. The whorled sunflower grows in prairie-like habitats, open flood plains and wet depressions near the edges of forests in large clonal clumps that can reach three meters in height. The vigorous growth and showy yellow flowers may render the species a potential valuable ornamental plant and presumably a useful pollinizer in the wild as well as in the home garden, which is common for other sunflower species. As a result of documented habitat loss, high self pollination rates, and high clonal reproduction which resulted in a loss of genetic diversity, the species was classified as a federally endangered species in 2014. Although progress has been made regarding genetic diversity in H. verticillatus populations, knowledge regarding basic biology, census data, and a lack of a well-defined conservation plan remain a major problem for preservation of this species. Therefore, researchers at the University of Tennessee and the USDA, ARS assessed clonal diversity and spatial distribution of H. verticillatus at two geographically close populations in Georgia to expand knowledge of the fine scale genetic diversity and population structure. Our results indicated moderate genetic diversity and presence of two distinct genetic populations. Additional analyses indicated high genetic differentiation and limited gene flow between collection sites. There was evidence of a population bottleneck that suggests a recent reduction in population size that could be explained by habitat loss and population fragmentation. In addition, support was found that individuals within these sites are primarily reproducing asexually. The results of this study provide a better understanding of fine-scale genetic diversity and spatial distribution of whorled sunflower populations in Georgia. Combined with previous research findings, our results can underpin a novel recovery plan for the species that can be utilized for conservation of this endangered species to promote its persistence in the wild.

Technical Abstract: Helianthus verticillatus, the whorled sunflower, is a plant endemic to four locations in Georgia, Alabama and Tennessee. The species has multiple showy yellow blooms making it a prime ornamental plant that is attractive to different pollinators. Helianthus verticillatus was designated as a federally endangered species in 2014 due to habitat loss. Despite its endangered status, there is no recovery plan for H. verticillatus and our knowledge related to basic plant biology and its importance in ecosystem services is largely unknown. Here, we utilized microsatellite loci to investigate fine-scale population structure and diversity of 206 H. verticillatus individuals found on two sampling sites within the Georgia population. Our results indicated moderate genetic diversity (Hexp = 0.50) and presence of two distinct genetic clusters. Analyses of molecular variance indicated that the majority of variance (51%, P<0.001) was individually based, thus confirming high genetic differentiation (Fst=0.20) and limited gene flow between H. verticillatus collection sites. The evidence of a population bottleneck in these sites suggests a recent reduction in population size that could be explained by habitat loss and population fragmentation. In addition, high levels of linkage disequilibrium were found, implying that individuals within these sites are primarily reproducing asexually. Results presented here provide a better understanding of fine-scale genetic diversity and spatial distribution of H. verticillatus populations in Georgia. Combined with previous research findings, our results can underpin a novel recovery plan for H. verticillatus that could be utilized for conservation of this endangered species to promote its persistence in the wild.