The genetic composition of founding populations plays a key role in determining invasion success. Despite this fact, the role of genetic variation on the potential distribution of invaders has rarely been investigated. Here, we integrate genomic data into ecological niche models (ENMs) to predict the distribution of globally invasive common ragweed (Ambrosia artemisiifolia) to Australia. We identified three genetic clusters of ragweed and used these clusters to construct separate ENMs. The predicted distribution of ragweed in Australia changed depending on the genetic composition and continent of origin of the source population. By quantifying this change, we identified source populations most likely to expand the ragweed distribution. As prevention remains the most effective method of invasive species management, our work provides a valuable way of ranking the threat posed by different populations to better inform management decisions.

The adaptive significance of polyploidy has been extensively debated and chromosome level genome assemblies of non-model polyploids can provide insight into this topic. The Australian grass, Bothriochloa decipiens, belongs to the BCD clade, a group with a complex history of hybridization and polyploidy. We sequenced, assembled and annotated a chromosomal level genome reference of Bothriochloa decipiens using linked read sequencing and proximity ligation scaffolding. Comparative analysis revealed that the species is a diploidized allotetraploid. We grouped the 20 major scaffolds, representing the 20 chromosomes, into the two subgenomes of the parental species using unique repeat signatures. We found evidence of biased fractionation as well as differences in the activity of TEs between the subgenomes prior to hybridization. Genes retained as duplicates were enriched for biological functions such as transcription and response to external stimuli such as drought, supporting theories of biased duplicate gene retention following WGD events. This is a widespread species with the ability to establish well on many soil types easily, making it useful for ecological restoration of Australian grasslands. This reference genome is a valuable resource for future population genomic research involving Australian grasses which may be helpful in decision making during the ecological restoration processes.

Biological invasions are accelerating, and invasive species can have large economic impacts as well as severe consequences for biodiversity. During invasions, species can interact, potentially resulting in hybridization. Here, we examined two Cakile species, C. edentula and C. maritima (Brassicaceae), that co-occur and may hybridize during range expansion in separate regions of the globe. Cakile edentula invaded each location first, while C. maritima established later, apparently replacing the former. We assessed the evidence for hybridization in western North America and Australia, where both species have been introduced, and identified source populations with 4561 SNPs using Genotype-by-Sequencing. Our results indicate that the C. edentula in Australia originated from one region of eastern North America while in western North America it is likely from multiple sources. The C. maritima in Australia were derived from at least two different parts of Europe while the introduction in western North America is from one. Although morphological evidence of hybridization is generally limited to mixed species populations in Australia and virtually absent elsewhere, our genetic analysis revealed relatively high levels of hybridization in Australia (58% hybrids) and supported the presence of hybrids in western North America (16%) and New Zealand. Hybrids might be commonly overlooked in invaders, as identification based solely on morphological traits may represent only the tip of the iceberg. Our study reveals a repeated pattern of invasion, hybridization and apparent replacement of one species by another, which offers an opportunity to investigate the role of hybridization and introgression during invasion.

Biological invasions are accelerating, and invasive species can have large economic impacts as well as severe negative consequences for biodiversity and ecosystems. During invasions, species can interact, potentially resulting in hybridization. Here, we examined two Cakile species, C. edentula and C. maritima (Brassicaceae), that co-occur and may hybridize during range expansion in separate regions of the globe. Cakile edentula invaded each location first, while C. maritima established later, apparently replacing the former. We assessed the evidence for hybridization in western North America and Australia, where both species have been introduced, and identified source populations with 4561 SNPs using Genotype-by-Sequencing. Our results indicate that the C. edentula in Australia originated from one region of eastern North America while in western North America it is likely from multiple sources. The C. maritima in Australia were derived from at least two different parts of Europe while the introduction in western North America is from a distinct source. Although morphological evidence of hybridization is generally limited to mixed populations in Australia and virtually absent elsewhere, our genetic analysis revealed relatively high levels of hybridization in Australia (34.13%), and supported the presence of hybrids in western North America (16.18%) and New Zealand. Hybrids might be commonly overlooked in invaders, as identification based solely on morphological traits may represent only the tip of the iceberg. Our study reveals a repeated pattern of invasion, hybridization and apparent replacement of one species by another, which offers an opportunity to investigate the role of hybridization and introgression during invasion.