Conservation in the face of hybridisation: genome-wide study to evaluate taxonomic delimitation and conservation status of a threatened orchid species

Abstract

This study assessed inter- and intraspecific relationships and genetic structure in an Australian species complex in the helmet orchids (Corybas) to clarify the taxonomic and conservation status of the threatened species Corybas dowlingii, a narrow endemic from southeast Australia. Taxonomic delimitation between the three closely related species C. aconitiflorus, C. barbarae, and C. dowlingii has been mainly based on floral traits which exhibit varying degrees of overlap, rendering species delimitation in the complex difficult. Genome-wide data for the species complex was generated using double-digest restriction-site associated DNA (ddRAD) sequencing. Phylogenomic, genetic network and genetic structure analysis were carried out as well as co-ancestry analysis and hybridisation detection analysis. The ddRADseq results exhibited fine scale genetic structure within the C. acotiniflorus complex and provided evidence for hybridisation and introgression within the complex, resulting in blurred taxonomic boundaries between the three species. Implications of the results for conservation management in the face of hybridisation are discussed.