Intercontinental dispersal of Typha angustifolia and T. latifolia between Europe and North America has implications for Typha invasions

Field-based measurement tools to distinguish clonal Typha taxa and estimate biomass: a resource for conservation and restoration

Two species of clonal Typha [T. latifolia (native) and T. angustifolia (exotic)] hybridize to form the highly invasive, heterotic (high vigor) T. × glauca in North American wetlands leading to increased primary production, litter accumulation, and biodiversity loss. Conservation of T. latifolia has become critical as invasive Typha has overwhelmed wetlands. In the field, Typha taxa identification is difficult due to subtle differences in morphology, and molecular identification is often unfeasible for managers. Furthermore, improved methods to non-destructively estimate Typha biomass is imperative to enhance ecological impact assessments. To address field-based Typha ID limitations, our study developed a predictive model from 14 Typha characters in 7 northern Michigan wetlands to accurately distinguish Typha taxa (n = 33) via linear discriminant analysis (LDA) of molecularly identified specimens. In addition, our study developed a partial least squares regression (PLS) model to predict Typha biomass from field collected measurements (n = 75). Results indicate that two field measurements [Leaf Counts, Longest Leaf] can accurately differentiate the three Typha taxa and advanced-generation hybrids. The LDA model had a 100% correct prediction rate of T. latifolia. The selected PLS biomass prediction model (sqrt[Typha Dry Mass] ~ log[Ramet Area at 30 cm] + Inflorescence Presence + Total Ramet Height + sqrt[Organic Matter Depth]) improved upon existing simple linear regression (SLR) height-to-biomass predictions. The rapid field-based Typha identification and biomass assessment tools presented in this study advance targeted management for regional conservation of T. latifolia and ecological restoration of wetlands impacted by invasive Typha taxa.

Evidence of hybrid breakdown among invasive hybrid cattails (Typha × glauca)

Interspecific hybridization has varied consequences for offspring fitness, with implications for the maintenance of species integrity. Hybrid vigour, when it occurs, can peak in first-generation (F1) hybrids and then decline in advanced-generation (F2+) hybrids. This hybrid breakdown, together with the processes affecting patterns of hybridization and hybrid fitness, determine the evolutionary stability of hybrid zones. An extensive hybrid zone in North America involving the cattails Typha latifolia, T. angustifolia, and their invasive hybrid T. × glauca is characterized by hybrid vigour among F1s, but the fitness of advanced-generation hybrids has not been studied. We compared seed germination and plant growth of T. latifolia (parental L), F1 T. × glauca (F1), hybrid backcrosses to T. angustifolia (bcA) and T. latifolia (bcL), and advanced-generation (F2) hybrids. Consistent with expectations under hybrid breakdown, we found reduced plant growth for F2 hybrids in comparison with F1s (plant height and above-ground biomass) and parental Ls (above-ground biomass). Backcrossed hybrids had intermediate measures of plant growth and bcLs were characterized by reduced seed germination in comparison with parental Ls. Hybrid breakdown could make the formation of F1s in North America finite because (1) hybridization among cattails is asymmetric, with T. angustifolia but not T. latifolia subject to genetic swamping, and (2) T. angustifolia is less common and subject to competitive displacement by F1s. Hybrid breakdown is therefore expected to reduce hybrid frequencies over time, contributing to the long-term maintenance of T. latifolia - the only native cattail in the study region.

Expression Level Dominance and Homeolog Expression Bias Upon Cold Stress in the F1 Hybrid Between the Invasive Sphagneticola trilobata and the Native S. calendulacea in South China, and Implications for Its Invasiveness

The role of hybridization is significant in biological invasion, and thermotolerance is a trait critical to range expansions. The South American Sphagneticola trilobata is now widespread in South China, threatening the native S. calendulacea by competition and hybridization. Furthermore, upon formation, their F1 hybrid can quickly replace both parents. In this study, the three taxa were used as a model to investigate the consequences of hybridization on cold tolerance, particularly the effect of subgenome dominance in the hybrid. Upon chilling treatments, physiological responses and transcriptome profiles were compared across different temperature points to understand their differential responses to cold. While both parents showed divergent responses, the hybrid’s responses showed an overall resemblance to S. calendulacea, but the contribution of homeolog expression bias to cold stress was not readily evident in the F1 hybrid possibly due to inherent bias that comes with the sampling location. Our findings provided insights into the role of gene expression in differential cold tolerance, and further contribute to predicting the invasive potential of other hybrids between S. trilobata and its congeners around the world.

Genome assembly, annotation, and comparative analysis of the cattail Typha latifolia

Cattails (Typha species) comprise a genus of emergent wetland plants with a global distribution. Typha latifolia and Typha angustifolia are two of the most widespread species, and in areas of sympatry can interbreed to produce the hybrid Typha × glauca. In some regions, the relatively high fitness of Typha × glauca allows it to outcompete and displace both parent species, while simultaneously reducing plant and invertebrate biodiversity, and modifying nutrient and water cycling. We generated a high-quality whole-genome assembly of T. latifolia using PacBio long-read and high coverage Illumina sequences that will facilitate evolutionary and ecological studies in this hybrid zone. Genome size was 287 Mb and consisted of 1158 scaffolds, with an N50 of 8.71 Mb; 43.84% of the genome were identified as repetitive elements. The assembly has a BUSCO score of 96.03%, and 27,432 genes and 2700 RNA sequences were putatively identified. Comparative analysis detected over 9000 shared orthologs with related taxa and phylogenomic analysis supporting T. latifolia as a divergent lineage within Poales. This high-quality scaffold-level reference genome will provide a useful resource for future population genomic analyses and improve our understanding of Typha hybrid dynamics.

Effects of invasive wetland macrophytes on habitat selection and movement by freshwater turtles

Invasive species can significantly impact native wildlife by structurally altering habitats and access to resources. Understanding how native species respond to habitat modification by invasive species can inform effective habitat restoration, avoiding inadvertent harm to species at risk. The invasive graminoids Phragmites australis australis (hereafter Phragmites) and Typha ×  glauca are increasingly dominating Nearctic wetlands, often outcompeting native vegetation. Previous research suggests that turtles may avoid invasive Phragmites when moving through their home ranges, but the mechanisms driving avoidance are unclear. We tested two hypotheses that could explain avoidance of invaded habitat: (1) that stands of invasive macrophytes (Phragmites and Typha x glauca) impede movement, and (2) that they provide inadequate thermal conditions for turtles. We quantified active-season movements of E. blandingii (n = 14, 1328 relocations) and spotted turtles (Clemmys guttata; n = 12, 2295 relocations) in a coastal wetland in the Laurentian Great Lakes. Neither hypothesis was supported by the data. Phragmites and mixed-species Typha stands occurred within the home ranges of mature, active E. blandingii and C. guttata, and were used similarly to most other available habitats, regardless of macrophyte stem density. Turtles using stands of invasive macrophytes did not experience restricted movements or cooler shell temperatures compared to other wetland habitat types. Control of invasive macrophytes can restore habitat heterogeneity and benefit native wetland species. However, such restoration work should be informed by the presence of at-risk turtles, as heavy machinery used for control or removal may injure turtles that use these stands as habitat.

Salinity, not genetic incompatibilities, limits the establishment of the invasive hybrid cattail Typha × glauca in coastal wetlands

Hybrids of a single pair of parent species can be much more common in some geographical regions than in others. The reasons for this are not well understood, but could help explain processes such as species diversification or the range expansion of invasive hybrids. The widespread cattails Typha latifolia and T. angustifolia seldom hybridize in some parts of their range, but in other areas produce the dominant hybrid T. × glauca. We used a combination of field and greenhouse experiments to investigate why T. × glauca has invaded wetlands in the Laurentian Great Lakes region of southern Ontario, Canada, but is much less common in the coastal wetlands of Nova Scotia (NS) in eastern Canada. One potentially important environmental difference between these two regions is salinity. We therefore tested three hypotheses: (1) T. latifolia and T. angustifolia in NS are genetically incompatible; (2) the germination or growth of T. × glauca is reduced by salinity; and (3) T. latifolia, a main competitor of T. × glauca, is locally adapted to saline conditions in NS. Our experiments showed that NS T. latifolia and T. angustifolia are genetically compatible, and that saline conditions do not impede growth of hybrid plants. However, we also found that under conditions of high salinity, germination rates of hybrid seeds were substantially lower than those of NS T. latifolia. In addition, germination rates of NS T. latifolia were higher than those of Ontario T. latifolia, suggesting local adaptation to salinity in coastal wetlands. This study adds to the growing body of literature which identifies the important roles that local habitat and adaptation can play in the distributions and characteristics of hybrid zones.

Salinity, not genetic incompatibilities, limits the establishment of the invasive hybrid cattail Typha × glauca in coastal wetlands

Hybrids of a single pair of parent species can be much more common in some geographical regions than in others. The reasons for this are not well understood, but could help explain processes such as species diversification or the range expansion of invasive hybrids. The widespread cattails Typha latifolia and T. angustifolia seldom hybridize in some parts of their range, but in other areas produce the dominant hybrid T. × glauca. We used a combination of field and greenhouse experiments to investigate why T. × glauca has invaded wetlands in the Laurentian Great Lakes region of southern Ontario, Canada, but is much less common in the coastal wetlands of Nova Scotia (NS) in eastern Canada. One potentially important environmental difference between these two regions is salinity. We therefore tested three hypotheses: (1) T. latifolia and T. angustifolia in NS are genetically incompatible; (2) the germination or growth of T. × glauca is reduced by salinity; and (3) T. latifolia, a main competitor of T. × glauca, is locally adapted to saline conditions in NS. Our experiments showed that NS T. latifolia and T. angustifolia are genetically compatible, and that saline conditions do not impede growth of hybrid plants. However, we also found that under conditions of high salinity, germination rates of hybrid seeds were substantially lower than those of NS T. latifolia. In addition, germination rates of NS T. latifolia were higher than those of Ontario T. latifolia, suggesting local adaptation to salinity in coastal wetlands. This study adds to the growing body of literature which identifies the important roles that local habitat and adaptation can play in the distributions and characteristics of hybrid zones.

Genetic structure in hybrids and progenitors provides insight into processes underlying an invasive cattail (Typha × glauca) hybrid zone

Traditional models of hybrid zones have assumed relatively low hybrid fitness, and thus focussed more on interspecific gene flow than on hybrid dispersal. Therefore, when hybrids have high fitness and the potential for autonomous dispersal, we have limited understanding of whether hybrid dispersal or repeated local hybrid formation is more important for maintaining hybrid zones. The invasive hybrid cattail Typha × glauca occupies an extensive hybrid zone in northeastern North America where it is sympatric with its progenitors T. latifolia and T. angustifolia. We characterized genetic diversity and genetic structure of the three taxa across a broad spatial scale where the maternal parent is relatively rare, and tested the hypothesis that the hybrid shows stronger evidence of gene flow than its progenitor species, particularly among disturbed sites (ditches) compared with established wetlands. Support for this hypothesis would suggest that dispersal, rather than repeated local formation, is more important for maintaining hybrid zones. Within each taxon, genetic differentiation among ditches was comparable to that among wetlands, although clonal richness was consistently greater in ditches, suggesting more frequent seed establishment. Genetic structure across sites was more pronounced in the hybrid compared with either progenitor species. Overall, our data reflect relatively low gene flow in hybrids, and suggest that hybrids are more likely to be created in situ than to be introduced from other sites. Despite the high fitness of invasive T. × glauca and its potential for autonomy, local processes appear more important than dispersal in maintaining this hybrid zone.

Revised phylogeny and historical biogeography of the cosmopolitan aquatic plant genus Typha (Typhaceae)

Typha is a cosmopolitan aquatic plant genus that includes species with widespread distributions. It is a relatively ancient genus with an abundant fossil record dating back to the Paleogene. However, the details of its biogeographic history have remained unclear until now. In this study, we present a revised molecular phylogeny using sequences of seven chloroplast DNA markers from nine species sampled from various regions in order to infer the biogeographic history of the genus. Two clades were recovered with robust support. Typha minima and T. elephantina comprised one clade, and the other clade included the remaining seven species, which represented a polytomy of four robustly supported subclades. Two widespread species, T. angustifolia and T. domingensis, were revealed to be paraphyletic, indicating the need for taxonomic revision. Divergence time estimation suggested that Typha had a mid-Eocene crown origin, and its diversification occurred in the Middle and Late Miocene. Ancestral area reconstruction showed that Typha possibly originated from eastern Eurasia. Both dispersal via the Beringian Land Bridge and recent transoceanic dispersal may have influenced the intercontinental distribution of Typha species.