Genomic evidence for widespread hybridization and demographic history in invasive saltcedar

Biological invasions provide opportunities for previously isolated lineages to come into secondary contact, often resulting in hybridization. This process can generate admixed genomes and novel phenotypes, potentially contributing to invasion success. Here, we investigated invasive saltcedar (Tamarix spp.) in the southwestern United States using genome-wide SNP data from 319 individuals, including the parental lineages Tamarix chinensis and T. ramosissima. By integrating population genomics, ecological niche modeling, and demographic inference, we reconstructed the origins of invasive populations and characterized admixture across major river basins. Our results reveal that introduced populations are predominantly admixed, with varying ancestry contributions from both parental lineages. Multiple lines of evidence, including hybrid indices, f3-statistics, and phylogenetic network analyses, support extensive admixture among US populations. Demographic inference indicates a recent origin consistent with historical introduction records and suggests that admixed propagules were likely introduced and subsequently expanded. Furthermore, ecological niche analyses suggest significant differentiation and niche expansion in the introduced populations compared to their native parental counterparts. Together, these results demonstrate that hybridization, together with multiple introductions and demographic processes, contributed to the maintenance of neutral genetic diversity and may have facilitated the successful establishment of these invasive populations. More broadly, this study highlights how integrating genomic data with ecological niche analyses clarifies the evolutionary dynamics during biological invasions.