Phylogenomics and genetic admixture of the invasive fireweed complex (Senecio inaequidens–Senecio madagascariensis) at a global scale
摘要
The southern African Senecio inaequidens–S. madagascariensis complex, (‘fireweed complex’), contains several species that have established as weeds outside of their native ranges. Senecio madagascariensis is the most widespread, found in Mexico, South America, Japan, Australia, New Zealand, and the Hawaiian Islands. Species delimitation in the complex is controversial, and identification of specimens is difficult. Biological control researchers have worked under the assumption that invasive populations of S. madagascariensis originated in the KwaZulu-Natal province of South Africa. Recently, phylogenetic analysis of target capture data from hundreds of genes found the KwaZulu-Natal specimens of S. madagascariensis forming a sister group to nearly all specimens of the invasive lineage of that species, raising doubt about the established provenance of the latter. Here, we vastly expanded geographic sampling of the fireweed complex. Our results confirm that Madagascan S. madagascariensis is distantly related to continental African and invasive populations. If the two were taxonomically separated, the name S. ruderalis would be available for the invasive populations. Most continental African populations formed one clade with South American and few Australian specimens. All other specimens from invaded areas formed a clade with a single specimen from Eastern Cape province, South Africa, suggesting that invasive populations outside of South America may mostly be derived from the southernmost part of the native range. Taken together with recent studies showing differences in defence chemistry and performance of a candidate biocontrol agent between KwaZulu-Natal and Australian populations, these results imply that more research is needed into the area of origin of invasive populations and their associated candidate biocontrol agents.