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

## TL;DR

This study uses genetic analysis to trace the invasion pathways of a South African iceplant that has become invasive in North America.

## Contribution

The study identifies a bridgehead invasion pattern and recommends focusing biological control efforts on the native South African range.

## Key findings

- The species originated in South Africa, with higher genetic diversity and private alleles observed there.
- A secondary invasion from Mediterranean populations to North America is supported, rather than a direct invasion from South Africa.
- Biological control agent surveys should prioritize the native South African range due to higher diversity of natural enemies.

## Abstract

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.

Mesembryanthemum nodiflorum
is a species of ice plant native to South Africa that has become invasive in California and Mexico. The present study used RADseq data to run a population genetics analysis to match the invasive populations to those in the native and introduced ranges of the Mediterranean. The results supported a secondary invasion of the plant from the introduced populations in the Mediterranean to North America, and that surveys for biological control agents should focus on the native range in South Africa.