Biogeographic Variation in Resistance of the Invasive Plant, Alliaria Petiolata, to a Powdery Mildew Fungus and Effect of Resistance on Competitive Dynamics

Garlic mustard is an invasive Eurasian biennial that has spread throughout the eastern United States and southern Canada. Populations of this plant vary in their susceptibility to Erysiphe cruciferarum, a causal agent of powdery mildew disease in Brassicaceous plants. We examined whether there were biogeographic patterns in the distribution of resistance in invasive North American and native European populations of this plant. We grew plants from 78 invasive and 20 native populations and screened them for powdery mildew resistance in the greenhouse. We found that populations were mostly monomorphic for either resistance or susceptibility but that some polymorphic populations were found from both continents. The proportion of populations showing resistance versus susceptibility was similar in both Europe and North America. Within continents, the spatial distribution of resistant and susceptible populations did not deviate significantly from random. We also examined whether the possession of the resistance trait alter intraspecific competitive dynamics. In two trials, we competed plants from resistant and susceptible populations in a target-neighbor design in the presence and absence of powdery mildew inoculum and examined the growth of the target plant. Target plants from resistant populations were overall larger than target plants from susceptible populations. Target plants were overall larger when grown in competition with susceptible neighbors. Further, resistant target plants showed a greater degree of release from competition when grown with a susceptible neighbor versus a resistant neighbor than the degree of release shown by susceptible target plants. This suggests a benefit of possessing the resistance trait with little apparent costs which should promote selection for this trait within plant populations

Biogeographic Variation in Resistance of the Invasive Plant, Alliaria Petiolata, to a Powdery Mildew Fungus and Effect of Resistance on Competitive Dynamics

Garlic mustard is an invasive Eurasian biennial that has spread throughout the eastern United States and southern Canada. Populations of this plant vary in their susceptibility to Erysiphe cruciferarum, a causal agent of powdery mildew disease in Brassicaceous plants. We examined whether there were biogeographic patterns in the distribution of resistance in invasive North American and native European populations of this plant. We grew plants from 78 invasive and 20 native populations and screened them for powdery mildew resistance in the greenhouse. We found that populations were mostly monomorphic for either resistance or susceptibility but that some polymorphic populations were found from both continents. The proportion of populations showing resistance versus susceptibility was similar in both Europe and North America. Within continents, the spatial distribution of resistant and susceptible populations did not deviate significantly from random. We also examined whether the possession of the resistance trait alter intraspecific competitive dynamics. In two trials, we competed plants from resistant and susceptible populations in a target-neighbor design in the presence and absence of powdery mildew inoculum and examined the growth of the target plant. Target plants from resistant populations were overall larger than target plants from susceptible populations. Target plants were overall larger when grown in competition with susceptible neighbors. Further, resistant target plants showed a greater degree of release from competition when grown with a susceptible neighbor versus a resistant neighbor than the degree of release shown by susceptible target plants. This suggests a benefit of possessing the resistance trait with little apparent costs which should promote selection for this trait within plant populations

Biogeographic Variation in Resistance of the Invasive Plant, Alliaria Petiolata, to a Powdery Mildew Fungus and Effect of Resistance on Competitive Dynamics

Garlic mustard is an invasive Eurasian biennial that has spread throughout the eastern United States and southern Canada. Populations of this plant vary in their susceptibility to Erysiphe cruciferarum, a causal agent of powdery mildew disease in Brassicaceous plants. We examined whether there were biogeographic patterns in the distribution of resistance in invasive North American and native European populations of this plant. We grew plants from 78 invasive and 20 native populations and screened them for powdery mildew resistance in the greenhouse. We found that populations were mostly monomorphic for either resistance or susceptibility but that some polymorphic populations were found from both continents. The proportion of populations showing resistance versus susceptibility was similar in both Europe and North America. Within continents, the spatial distribution of resistant and susceptible populations did not deviate significantly from random. We also examined whether the possession of the resistance trait alter intraspecific competitive dynamics. In two trials, we competed plants from resistant and susceptible populations in a target-neighbor design in the presence and absence of powdery mildew inoculum and examined the growth of the target plant. Target plants from resistant populations were overall larger than target plants from susceptible populations. Target plants were overall larger when grown in competition with susceptible neighbors. Further, resistant target plants showed a greater degree of release from competition when grown with a susceptible neighbor versus a resistant neighbor than the degree of release shown by susceptible target plants. This suggests a benefit of possessing the resistance trait with little apparent costs which should promote selection for this trait within plant populations

Why Has U.S. Policy Uncertainty Risen Since 1960?

Abstract: There appears to be a strong upward drift in policy-related economic uncertainty after 1960. We consider two classes of explanations for this rise. The first stresses growth in government spending, taxes, and regulation. A second stresses increased political polarization and its implications for the policy-making process and policy choices. While the evidence is inconclusive, it suggests that both factors play a role in driving the secular increase in policy uncertainty over the last half century

Sublethal Effects of Acoustic Dummy Tag Implantation and External Tags in Silver Carp

Telemetry data collected via internally implanted transmitters are commonly used to monitor and manage invasive Silver Carp Hypophthalmichthys molitrix. However, the extent to which posttagging effects may influence fish behavior is generally overlooked in telemetry studies. Moreover, internal telemetry tags are often combined with an external tag that can also affect fish growth and survival. This study used two pond experiments to (1) evaluate the temporal effects of internal telemetry tags, external jaw tags, and the combination of the two tags on survival, relative weight, growth, and inflammation; and (2) compare the effects of two external tag types (jaw and loop tags) on Silver Carp. Response variables were evaluated at three time points: 1, 2, and 5 months posttagging. Growth and relative weight were lower in fish that received jaw tags than in the control group or in fish that received internal tags only; however, growth was different at 1 month posttagging but not at 2 months posttagging, indicating potential compensatory growth. Shedding rate of internal tags was 14%; after 5 months, inflammation was absent and tags were encapsulated in tissue. Survival was similar between loop- and jaw-tagged fish (73%), although growth was lower in jaw-tagged fish. Results indicate that survival effects and sublethal effects of telemetry tagging may be temporary, and researchers should examine detection data from within 1–2 months of tagging for possible postsurgery effects. Jaw tags reduced growth, and loop tags had reduced retention; therefore, further evaluation of alternative external tags is needed to optimize telemetry studies focused on Silver Carp. Additionally, researchers need to carefully evaluate which external tag to use to facilitate the returns of more expensive acoustic telemetry tags and whether external tags are necessary in a particular case