Population Genetics Reveals the Invasion Pathways of Mesembryanthemum nodiflorum in North America

Invasive populations of the slenderleaf iceplant, Mesembryanthemum nodiflorum L., are problematic along the west coast of North America. The plant is hypothesised to originate from southern Africa, though it has established populations in North Africa and the Mediterranean. There is interest in initiating a biological control programme for the weed in its invaded range, but a clearer understanding of its invasion pathways and sources of origin is required in order to prioritise potential biological control agents. This study used both NextGen RADseq and fragment analysis ISSR techniques to uncover the population structure and genetic diversity of M. nodiflorum in its native, introduced and invaded ranges. The results supported a South African origin of the species based on a higher number of private alleles and overall genetic diversity. Our results suggest a bridgehead effect, where a secondary invasion to North America from Mediterranean populations took place, rather than a direct invasion from the native range in South Africa. The present results indicated that surveys for potential biocontrol agents for M. nodiflorum should be conducted in the native South African distribution, where the greatest diversity of specialist natural enemies is likely to be present.