Population genomic and historical analysis suggests a global invasion by bridgehead processes in Mimulus guttatus

Abstract

Imperfect historical records and complex demographic histories present challenges for reconstructing the history of biological invasions. Here, we combine historical records, extensive worldwide and genome-wide sampling, and demographic analyses to investigate the global invasion of Mimulus guttatus from North America to Europe and the Southwest Pacific. By sampling 521 plants from 158 native and introduced populations genotyped at >44,000 loci, we determined that invasive M. guttatus was first likely introduced to the British Isles from the Aleutian Islands (Alaska), followed by admixture from multiple parts of the native range. We hypothesise that populations in the British Isles then served as a bridgehead for vanguard invasions worldwide. Our results emphasise the highly admixed nature of introduced M. guttatus and demonstrate the potential of introduced populations to serve as sources of secondary admixture, producing novel hybrids. Unravelling the history of biological invasions provides a starting point to understand how invasive populations adapt to novel environments.

The evolution of thermal performance in native and invasive populations ofMimulus guttatus

“…Insufficient standing genetic variation could contribute to the evolutionary stasis of TPC parameters in the invasive range (Dlugosch et al 2015;Prentis et al 2008), but the highly admixed nature of invasive M. guttatus populations has allowed for maintenance of relatively high genetic diversity (Puzey and Vallejo-Marín 2014;Pantoja et al 2017;Vallejo-Marín et al 2021). These high levels of genetic variation likely contributed to the maintenance of broad TPCs and allowed these populations to easily tolerate the narrower range of temperatures in the invasive U.K. range.…”

“… 2017 ), followed by multiple introductions of perennial populations from across the native range (Vallejo‐Marín et al. 2021 ). The invasive U.K. range thus consists of a highly admixed melting pot of native populations and is not likely constrained by low genetic diversity (Puzey and Vallejo‐Marín 2014 ; Pantoja et al.…”

“…In 1812, M. guttatus was brought to the United Kingdom for horticultural use and has subsequently become widespread across the British Isles and to a lesser extent parts of continental Europe (Preston et al 2002;Truscott et al 2008;Newman 2015). Genomic data suggest that genotypes of M. guttatus in the United Kingdom originated from perennial populations in Alaska (Puzey and Vallejo-Marín 2014;Pantoja et al 2017), followed by multiple introductions of perennial populations from across the native range (Vallejo-Marín et al 2021). The invasive U.K. range thus consists of a highly admixed melting pot of native populations and is not likely constrained by low genetic diversity (Puzey and Vallejo-Marín 2014;Pantoja et al 2017;Vallejo-Marín et al 2021).…”

Temporal matches and mismatches between monarch butterfly and milkweed population changes over the past 12,000 years

“…In this study we employ an ABC-RF approach to study the near-term demographic history of monarchs and milkweeds. This approach was chosen in part because it has proven useful in other systems in elucidating very recent demographic events, within decades or centuries (Vallejo-Marín et al 2021; Fraimout et al 2017). In addition, this approach requires fewer simulated datasets to train the classifier than are necessary for traditional ABC, and it is much more robust to choices of summary statistics (Pudlo et al 2016; Csilléry, François, and Blum 2012).…”

“…To reconstruct the demographic histories of monarchs and milkweed, here we use Approximate Bayesian Computation with Random Forests (ABC-RF) . This approach has recently been employed by a number of population genetic studies on a diverse array of organisms, including humans (Estoup et al 2018), insects (Lombaert et al, n.d.), plants (Nevado et al 2020), chordates (Smith et al 2018), and pathogens (Schwabl et al 2021), and it has been used to reconstruct biological invasions and other demographic events happening within the past few decades or centuries (van Boheemen et al 2017;Vallejo-Marín et al 2021;Fraimout et al 2017).…”