No evidence for niche segregation in a North American Cattail (Typha) species complex

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.