Genomics reveals the history of a complex plant invasion and improves the management of a biological invasion from the South African–Australian biotic exchange

Abstract

Many plants exchanged in the global redistribution of species in the last 200 years, particularly between South Africa and Australia, have become threatening invasive species in their introduced range. Refining our understanding of the genetic diversity and population structure of native and alien populations, introduction pathways, propagule pressure, naturalization, and initial spread, can transform the effectiveness of management and prevention of further introductions. We used 20,221 single nucleotide polymorphisms to reconstruct the invasion of a coastal shrub, Chrysanthemoides monilifera ssp. rotundata (bitou bush) from South Africa, into eastern Australia (EAU), and Western Australia (WAU). We determined genetic diversity and population structure across the native and introduced ranges and compared hypothesized invasion scenarios using Bayesian modeling. We detected considerable genetic structure in the native range, as well as differentiation between populations in the native and introduced range. Phylogenetic analysis showed the introduced samples to be most closely related to the southern‐most native populations, although Bayesian analysis inferred introduction from a ghost population. We detected strong genetic bottlenecks during the founding of both the EAU and WAU populations. It is likely that the WAU population was introduced from EAU, possibly involving an unsampled ghost population. The number of private alleles and polymorphic SNPs successively decreased from South Africa to EAU to WAU, although heterozygosity remained high. That bitou bush remains an invasion threat in EAU, despite reduced genetic diversity, provides a cautionary biosecurity message regarding the risk of introduction of potentially invasive species via shipping routes.

Supplementary material 1 from: Castillo ML, Schaffner U, Mbaabu PR, Shiferaw H, van Wilgen BW, Eckert S, Choge S, Münzbergová Z, Le Roux JJ (2024) Following in the footsteps of invasion: comparisons of founder and invasive genotypes of two independent invasions reveal site-specific demographic processes and no influence by landscape attributes on dispersal. NeoBiota 93: 263-291. https://doi.org/10.3897/neobiota.93.117457

“…Genetic studies on naturalised and invasive populations have also contributed to our understanding of the drivers of invasion success, including the factors that underlie establishment and spread (Baker and Stebbins 1965;Le Roux, 2021). This knowledge, in turn, has provided important information for predicting the eco-evolutionary dynamics of invasive populations to assist their management (Funk et al 2020;Morisette et al 2021;Byrne et al 2022). For example, genetic analyses can be used to infer patterns of past spread (Cushman 2015), modes of dispersal (longvs short-distance; Sexton et al 2014;Smith et al 2020), or to understand the stochastic demographic events (i.e., genetic drift) or evolutionary processes (i.e., selection) that have shaped the genetic diversity present in invasive populations (Dlugosch and Parker 2008;van Boheemen et al 2018;Le Roux 2021).…”

Following in the footsteps of invasion: comparisons of founder and invasive genotypes of two independent invasions reveal site-specific demographic processes and no influence by landscape attributes on dispersal

“…Genetic studies on naturalised and invasive populations have also contributed to our understanding of the drivers of invasion success, including the factors that underlie establishment and spread (Baker and Stebbins 1965;Le Roux, 2021). This knowledge, in turn, has provided important information for predicting the eco-evolutionary dynamics of invasive populations to assist their management (Funk et al 2020;Morisette et al 2021;Byrne et al 2022). For example, genetic analyses can be used to infer patterns of past spread (Cushman 2015), modes of dispersal (longvs short-distance; Sexton et al 2014;Smith et al 2020), or to understand the stochastic demographic events (i.e., genetic drift) or evolutionary processes (i.e., selection) that have shaped the genetic diversity present in invasive populations (Dlugosch and Parker 2008;van Boheemen et al 2018;Le Roux 2021).…”

Genome size estimation of false daisy, cheek weed, pot marigold and marigold

“…Important members of Asteraceae family include the false diasy ( Eclipta prostrate ), cheek weed ( Ageratum conyzoides ), pot marigold ( Calendula officinalis ), and marigold ( Tagetes erecta ), the strong, straight and ornamental marigold plant is cultivated as an ordinary nursery plant around the world [ 1 ]. Pot marigold, on the other hand, is one of the commonly used medicinal plants in China, India, the United States, and Europe [ 2 ]. Another plant under study in this area is cheek weed, an annual herb with straight, branching stems and thin, durable roots; there are numerous well-established restorative uses for cheek weed in numerous nations around the world [ 3 ].…”

“…However, fundamental studies like estimating these species' genome sizes will speed up genomics efforts. There has only been one report on flow cytometry-based estimates of the nuclear DNA concentration of Calendula officinalis to yet [ 2 ]. Estimating the genome size, in term as the "C value," has become a recognised application in a variety of biological experiments.…”