Hybrid watermilfoil (Myriophyllum spicatum × Myriophyllum sibiricum) exhibits traits associated with greater invasiveness than its introduced and native parental taxa

Hybridization has been associated with increased invasiveness in plants. In North America, the hybrid aquatic plant Myriophyllum spicatum × Myriophyllum sibiricum (hybrid watermilfoil, hereafter HWM) is a cross between non-native invasive Eurasian watermilfoil (M. spicatum, EWM) and native northern watermilfoil (M. sibiricum, NWM). Lab-based trials have demonstrated higher growth rates in HWM compared to EWM and NWM, but these patterns have not been systematically examined in the field. In this study, we compared the invasiveness of HWM to its parental taxa, EWM and NWM, by examining the amount and timing of: (1) flowering, (2) surface cover, and (3) biomass (using stem counts as a proxy). We conducted repeat surveys of Myriophyllum beds at eight lakes (2–3 lakes/taxon) in the Minneapolis–St. Paul Metropolitan area (Minnesota, USA) between June 2017 and November 2018. HWM produced more flower spikes earlier and overall, and maintained consistently more flower spikes throughout the growing season than EWM and NWM. In addition, surface cover reached greater annual peaks and was higher for longer throughout the growing season for HWM than for both parental taxa. We did not observe a significant difference in stem counts among the three taxa, but HWM did reach a higher maximum number of stems than either parental taxon. This study provides field-based evidence of increased invasiveness associated with hybridization between EWM and NWM; specifically, greater reproductive potential via flowering and greater surface cover may increase HWM spread, have greater impacts on native species, and pose more of a nuisance to lake users.

Identification of resistant clones of Eurasian (Myriophyllum spicatum) and hybrid (Myriophyllum spicatum × Myriophyllum sibiricum) watermilfoil to an operational rate of fluridone

Genetic assays to identify herbicide-resistant plants are a promising tool to reduce herbicide failures. However, the genetic basis of herbicide resistance is frequently unknown. In clonal weed species, DNA fingerprinting could be a useful tool to identify known resistant versus susceptible genets (clones) that occur in multiple locations, without an immediate need for understanding the genetic mutation(s) conferring resistance. Eurasian watermilfoil (Myriophyllum spicatum L.) and hybrids with native northern watermilfoil (Myriophyllum spicatum × Myriophyllum sibiricum Kom.) are mostly clonal invasive aquatic plants, and the same clones can be found in multiple waterbodies. Previously, a clone was confirmed as resistant to the commonly used herbicide fluridone, and a recent genetic survey in Michigan identified this genotype (MG-237) in at least seven other lakes. We hypothesized that MG-237 collected from different lakes would also exhibit fluridone resistance. However, MG-237 may have accumulated resistance mutations at different times during its spread across Michigan, resulting in fluridone-resistant and fluridone-susceptible MG-237 clones distributed in different lakes. We used a herbicide assay to test the response of several accessions, including MG-237 accessions from multiple lakes, to the Michigan operational rate of 6 µg L−1 fluridone. We found that all accessions of MG-237 exhibited resistance to 6 µg L−1 fluridone. A second genotype (MG-377) was also resistant to 6 µg L−1 fluridone. The rest of the accessions were found to be significantly injured by 6 µg L−1 fluridone. Our results suggest that 6 µg L−1 fluridone would not effectively control waterbodies dominated by MG-237 or MG-377, whereas waterbodies dominated by the other genotypes in our study would likely be controlled. Although more studies are needed to identify the variation in sensitivity of the accessions tested here and the genetic basis of fluridone resistance in Myriophyllum, our results suggest that multilocus genotype data may be an effective tool to identify and track herbicide-resistant genotypes of Myriophyllum in the short term.

Genetic diversity and differentiation in populations of invasive Eurasian (Myriophyllum spicatum) and hybrid (Myriophyllum spicatum × Myriophyllum sibiricum) watermilfoil

Population genetic studies of within- and among-population genetic variability are still lacking for managed submerged aquatic plant species, and such studies could provide important information for managers. For example, the extent of within-population genetic variation may influence the potential for managed populations to locally adapt to environmental conditions and control tactics. Similarly, among-population variation may influence whether specific control tactics work equally effectively in different locations. In the case of invasive Eurasian watermilfoil (Myriophyllum spicatum L.), including interspecific hybrids with native northern watermilfoil (Myriophyllum sibiricum Kom.), managers recognize that there is genetic variation for growth and herbicide response. However, it is unclear how much overall genetic variation there is, and how it is structured within and among populations. Here, we studied patterns of within- and among-lake genetic variation in 41 lakes in Michigan and 62 lakes in Minnesota using microsatellite markers. We found that within-lake genetic diversity was generally low, and among-lake genetic diversity was relatively high. However, some lakes were genetically diverse, and some genotypes were shared across multiple lakes. For genetically diverse lakes, managers should explicitly recognize the potential for genotypes to differ in control response and should account for this in monitoring and efficacy evaluation and using pretreatment herbicide screens to predict efficacy. Similarly, managers should consider differences in genetic composition among lakes as a source of variation in the growth and herbicide response of lakes with similar control tactics. Finally, laboratory or field information on control efficacy from one lake may be applied to other lakes where genotypes are shared among lakes.

THE EFFECT OF CLIMATIC SHIFTS ON BIODIVERSITY OF PHYTOCENOSIS: LAKE ARAKHLEY (EASTERN SIBERIA, RUSSIA)

Lake Arakhley is located within the Lake Baikal basin in Eastern Siberia, Russia. The area is characterized by continental subarctic climate with considerate diurnal temperature range, long cold dry winters and short hot summers with more precipitation occurring during the latter half of the summer. Climatic shifts in high water years and low water years result in morphometric changes in the lake and in the chemical and physical parameters of the ecosystem. During low water years, concentrations of ammonium nitrogen and nitrite nitrogen are decreased, whereas nitrate concentration increases. High water years feature average concentrations of ammonium ions 1.5–2 times higher than the values of recent dry years. Redundancy analysis (RDA) of abiotic factors and biotic community indicated that the community structure shows the greatest correlation with physical and chemical parameters of water and biogenic elements (nitrites, ammonium, phosphates) along the first axis, and with the lake depth and transparency along the second axis. Changes in abiotic factors induce functioning and formation of characteristic communities of the primary producers in the trophic structure of the ecosystem. During low water years, with increased level of autochthonous organic matter, Lindavia comta dominance is observed, while during high water years, with increased allochthonous organic matter Asterionella formosa appeared as dominant. Currently, during low water years, the hydrophytes community is monodominant and composed of Ceratophyllum demersum. Meanwhile, such species indicating eutrophic conditions as Myriophyllum sibiricum, Potamogeton pectinatus are found in the lake vegetation.

A PCR-RFLP method to detect hybridization between the invasive Eurasian watermilfoil (Myriophyllum spicatum) and the native northern watermilfoil (Myriophyllum sibiricum), and its application in Ontario lakes

The discovery of hybridization between the invasive Eurasian watermilfoil (Myriophyllum spicatum L.) and native northern watermilfoil (Myriophyllum sibiricum Kom.) has generated interest in establishing the hybrid’s distribution and invasiveness. Identification of hybrid M. spicatum × M. sibiricum requires molecular genetic analysis, however, as the hybrid’s morphology overlaps with both parent species. Using plants collected from 10 lakes in Ontario, Canada, we compared a previous method of identification (sequencing the nuclear ITS region) with a simpler screening method (PCR-RFLP of the ITS region). Both methods agreed on the identification of hybrid M. spicatum × M. sibiricum and both parent species, supporting the suitability of PCR-RFLP to screen for the hybrid. Four of 29 samples were identified as hybrid M. spicatum × M. sibiricum, which were all found in three adjacent lakes associated with the Rideau Canal Waterway. The PCR-RFLP method should enable greater sampling effort to screen for hybrid M. spicatum × M. sibiricum and establish its geographic distribution across connected waterways.

Annotated checklist to the vascular plant flora of Tuktut Nogait National Park and the Melville Hills region (Canadian Low Arctic)

Tuktut Nogait National Park is located in the Melville Hills in the northeastern corner of mainland Northwest Territories in Canada's Southern Arctic Ecozone. The first major floristic survey of the Melville Hills region was conducted in 1990 as part of a natural resource inventory to determine its suitability as a National Park. We studied the flora and made extensive plant collections in Tuktut Nogait National Park and the Melville Hills region in 2009. Here, we present a comprehensive annotated checklist to the region's vascular plant flora based on a review of all existing and our own new collections. This includes the citation of all specimens examined, colour photographs for a subset of taxa and detailed taxonomic comments. The Melville Hills flora comprises 268 taxa (265 species and three additional infraspecific taxa), a 16% increase from the first survey, 215 of which are known from Tuktut Nogait National Park. Forty-eight taxa are newly recorded for the region and 54 taxa are newly recorded for Tuktut Nogait National Park. Noteworthy records include range extensions for Botrychium lunaria, Carex concinna, Draba borealis, Myriophyllum sibiricum, Plantago eriopoda, Poa alpina, Poa ammophila, Puccinellia banksiensis, Salix arbusculoides, and Selaginella selaginoides. The flora includes 19 vascular plant species of potential conservation concern in the Northwest Territories, including six assessed as "May Be At Risk", of which one occurs in the Park and 13 assessed as "Sensitive", of which eight occur in the Park.