Population genomics reveals global patterns of genetic diversity and population structure associated with human-mediated spread of the invasive vine, Cape ivy (Delairea odorata Lem.): Implications for biological control research

Abstract

We investigated global patterns of population genetic diversity and structure for the clonal invasive scrambler, Cape ivy (Delairea odorata Lem., family Asteraceae), to help optimise exploratory surveys of candidate biocontrol agents in its native range, South Africa. We collected more than 1000 Cape ivy samples from 122 populations throughout South Africa and its introduced ranges (Australia, New Zealand, mainland USA, Hawai’i and southern France), and performed population genetic diversity and structure analyses based on single nucleotypic polymorphisms (SNPs). On average, population genetic diversity values were six times higher in South Africa than all introduced populations, although these values were three times higher for the mainland USA populations than those in Australia, Hawai’i and New Zealand. Populations were strongly differentiated with limited gene flow between the native and introduced ranges (intercontinental scale) and between sites within each range (regional scale). All Australian, New Zealand, Hawai’ian and some Californian populations had Fst values approaching zero, likely arising from a single clonal accession derived from the same ancestral population, likely from the Western Cape Province of South Africa. The remaining mainland USA populations showed signs of multiple introductions and admixture patterns. Our results show that human-assisted dispersal of Cape ivy through the ornamental plant trade can overcome genetic (bottleneck) barriers to global invasion, especially for clonal accessions of the plant. We recommend that host-specificity testing of candidate biocontrol agents for Cape ivy in the Australian and New Zealand contexts should source agents from the Western Cape Province of South Africa.