Lythrum salicaria common garden under Neogalerucella herbivory

We transplanted1088 seedlings of the invasive perennial plant Lythrum salicaria (purple loosestrife), from 136 maternal families sourced from 17 populations in the region around Ottawa, Canada, into a common garden containing 4 plots. The 17 populations differed in their prior exposure to the biocontrol agent Neogalerucella spp. leaf beetles (naïve = no prior exposure; recent = secondary colonization, ~5-15 years; release = sites of biocontrol release, ~20 years ago). Plants were planted in a wetland containing other Lythrum plants and experienced ambient (but significant) herbivory by Neogalerucella spp. leaf beetles. We measured herbivory, plant size and biomass over a period of 3.5 years; see the publication for more details. This experiment used the same seed material as a previously published greenhouse study by Stastny & Sargent 2017 (see below). Additional datasets, such as the proportion and phenology of flowering individuals, leaf size, stem and meristem numbers, etc., are available upon request.

Methods
At the time of transplanting (year 1), we measured plant height, corresponding to the variation in growth under greenhouse conditions. Afterwards, in years 2 and 3, we measured the sum length of all stems (mm); this metric corresponds to the early-season plant size prior to Neogalerucella herbivory, and gives an indication of the variation in regrowth and phenology early in the season. In year 4, when we terminated the common garden, we measured this metric directly as dry above-ground biomass (g). In the dataset, these three metrics are listed under parameters that include "size" in column header. In years 1-3, we visually estimated herbivory (as a reflection of the variation in resistance) for each plant, as percent defoliation (parameters that include “damage” in column header), i.e. the percentage of the leaf area removed by Neogalerucella feeding. This metric represents the main bout of herbivory in the growing season. Finally, at the end of each growing season in years 1-3 we measured above-ground biomass (parameters that include “biomass” in column header); this metric integrates the outcome of seasonal herbivory as well as any variation in tolerance to damage.