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PREMISE: Invasive species are expected to undergo a reduction in genetic diversity due to founder effects, which should limit their ability to adapt to new habitats. Still, many invasive species achieve widespread distributions and dense populations. This paradox of invasions could potentially be overcome through multiple introductions or hybridization, both of which increase genetic diversity. We conducted a population genomics study of Japanese knotweed (Reynoutria japonica), which is a polyploid, clonally reproducing invasive species that has been notoriously successful worldwide despite supposedly low genetic diversity. METHODS: We used genotyping by sequencing to collect 12,912 SNP markers from 88 samples collected at 38 locations across North America for the species complex. We used alignment‐free k‐mer hashing analysis in addition to traditional population genetic analyses to account for the challenges of genotyping polyploids. RESULTS: Genotypes conformed to three genetic clusters, likely representing Japanese knotweed, giant knotweed, and hybrid bohemian knotweed. We found that, contrary to previous findings, the Japanese knotweed cluster had substantial genetic diversity, though it had no apparent genetic structure across the landscape. In contrast, giant knotweed and hybrids showed distinct population groups. We did not find evidence of isolation by distance in the species complex, likely reflecting the stochastic introduction history of this species complex. CONCLUSIONS: The results indicate that clonal invasive species can show substantial genetic diversity and can be successful at colonizing a variety of habitats without showing evidence of local adaptation or genetic structure. [ABSTRACT FROM AUTHOR]

After polyploid species are formed, interactions between diploid and polyploid lineages may generate additional diversity in novel cytotypes and phenotypes. In anurans, mate choice by acoustic communication is the primary method by which individuals identify their own species and assess suitable mates. As such, the evolution of acoustic signals is an important mechanism for contributing to reproductive isolation and diversification in this group. Here, we estimate the biogeographical history of the North American grey treefrog complex, consisting of the diploid Hyla chrysoscelis and the tetraploid Hyla versicolor, focusing specifically on the geographical origin of whole genome duplication and the expansion of lineages out of glacial refugia. We then test for lineage-specific differences in mating signals by applying comparative methods to a large acoustic data set collected over 52 years that includes >1500 individual frogs. Along with describing the overall biogeographical history and call diversity, we found evidence that the geographical origin of H. versicolor and the formation of the midwestern polyploid lineage are both associated with glacial limits, and that the southwestern polyploid lineage is associated with a shift in acoustic phenotype relative to the diploid lineage with which they share a mitochondrial lineage. In H. chrysoscelis, we see that acoustic signals are largely split by Eastern and Western lineages, but that northward expansion along either side of the Appalachian Mountains is associated with further acoustic diversification. Overall, results of this study provide substantial clarity on the evolution of grey treefrogs as it relates to their biogeography and acoustic communication., (© 2023 John Wiley & Sons Ltd.)

[Display omitted] • Hybridization and polyploidy are common in the investigated complex of Isoëtes from western North America. • Ploidy differences are not strong barriers to hybridization. • Directionality of hybridization events may be dictated by gamete size differences between diploids and polyploids. • Low reproductive barriers may facilitate the high levels of hybridization between co-occurring species. Polyploidy and hybridization are important processes in seed-free plant evolution. However, a major gap lies in our understanding of how these processes affect the evolutionary history of high-ploidy systems. The heterosporous lycophyte genus Isoëtes is a lineage with many putative hybrids and high-level polyploid taxa (ranging from tetraploid to dodecaploid). Here, we use a complex of western North American Isoëtes , to understand the role of hybridization and high-level polyploidy in generating and maintaining novel diversity. To uncover these processes, we use restriction-site associated DNA sequencing (RADseq), multiple alleles of a single low-copy nuclear marker, whole plastomes, cytology (genome size estimates and chromosome counts), and reproductive status (fertile or sterile). With this dataset, we show that hybridization occurs easily between species in this complex and is bidirectional between identical, but not different, cytotypes. Furthermore, we show that fertile allopolyploids appear to have formed repeatedly from sterile homoploid and interploid hybrids. We propose that low prezygotic reproductive barriers and a high frequency of whole-genome duplication allow for high-level polyploid systems to generate novel lineages, and that these mechanisms may be important in shaping extant Isoëtes diversity. [ABSTRACT FROM AUTHOR]

Polyploid speciation has played an important role in evolutionary history across the tree of life, yet there remain large gaps in our understanding of how polyploid species form and persist. Although systematic studies have been conducted in numerous polyploid complexes, recent advances in sequencing technology have demonstrated that conclusions from data-limited studies may be spurious and misleading. The North American gray treefrog complex, consisting of the diploid Hyla chrysoscelis and the tetraploid H. versicolor, has long been used as a model system in a variety of biological fields, yet all taxonomic studies to date were conducted with only a few loci from nuclear and mitochondrial genomes. Here, we utilized anchored hybrid enrichment and high-throughput sequencing to capture hundreds of loci along with whole mitochondrial genomes to investigate the evolutionary history of this complex. We used several phylogenetic and population genetic methods, including coalescent simulations and testing of polyploid speciation models with approximate Bayesian computation, to determine that H. versicolor was most likely formed via autopolyploidization from a now extinct lineage of H. chrysoscelis. We also uncovered evidence of significant hybridization between diploids and tetraploids where they co-occur, and show that historical hybridization between these groups led to the re-formation of distinct polyploid lineages following the initial whole-genome duplication event. Our study indicates that a wide variety of methods and explicit model testing of polyploid histories can greatly facilitate efforts to uncover the evolutionary history of polyploid complexes., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Hyla chrysoscelis and H. versicolor are common treefrogs in eastern North America and are a cryptic diploid-tetraploid species pair. They are morphologically identical but H. versicolor is a tetraploid. They can be identified acoustically by the male's advertisement mating call, which has a pulse repetition rate that has twice as many pulses per second in the diploid species, H. chrysoscelis . We used isozymes, microsatellite DNA alleles, and mitochondrial cytochrome b sequences to test the hypothesis that gene exchange occurs between the diploid and tetraploid species in sympatric populations. Each method provided results that are best explained by occasional hybridization of female H. versicolor and male H . chrysoscelis. We propose that H. versicolor first arose from an autotriploid H. chrysoscelis female that produced unreduced triploid eggs. After H. versicolor became established, genes could be passed from H. chrysoscelis to H. versicolor in sympatric populations when these species hybridize. Their F 1 female progeny produce unreduced triploid eggs that are fertilized by haploid H. chrysoscelis sperm to reconstitute H. versicolor . Genes can be passed from diploid H . chrysoscelis to tetraploid H. versicolor in sympatric populations.