Has a weedy lifestyle evolved? Comparing variation of life history traits between invasive populations compared to their native counterparts.

Has a weedy lifestyle evolved? Comparing variation of life history traits between invasive populations compared to their native counterparts Jane Molofsky University of Vermont, Department of Plant Biology Results: Greenhouse Study Abstract: Studies of species within a genus indicate that certain life history traits are prevalent within invasive species. Traits associated with invasiveness include small seed mass, short juvenile period, high relative growth rate, and short periods between masting events (Grotkopp et al. 2002, Richardson and Rejmánek 2004). Using a relatively new invasive (spreading in Japan since 1990), our objectives were to determine how life history traits vary within species between ranges and whether a weedy lifestyle has evolved. We collected populations of a self-fertilizing, short-lived winter annual, hairy bittercress (Cardamine hirsuta) from two countries in its native European range (France and Malta) and two countries within its introduced range (Japan and the United States). Populations were grown under uniform greenhouse conditions and measured for differences in life history traits such as time between each stage (e.g. seed to seedling) and fecundity. Collected seeds were sown in a field experiment testing total lifetime fitness and life history traits under varying propagule pressure. High variation was found between the non-native and native genotypes, with non-natives having higher germination, flowering, and fecundity aiding in invasiveness. • From the initial common garden, we found there is variation in fecundity between ranges (Figure 1) and populations (nested within ranges). Plants from Japan and the U.S. produced more seeds than European plants (France and Malta). In the U.S. range, Vermont populations were similar in production to Japanese ones, while Massachusetts populations were similar to native French ones. AB Parent Ranges 2: Field: • Are there differences in how genotypes from different ranges respond to disturbance and planting density? Study Species: Cardamine hirsuta genotypes compare to their native • Life cycles were found to be more rapid in non-native USA genotypes than the native genotypes. B 50 25 0 Japan Europe Parent Range • Non-native genotypes have more aggressive (invasive) life history traits (e.g. short juvenile period, Japan fecundity 19.5x greater than Maltese, USA fecundity 9.2x greater than Maltese). Figure 1: Mean individual seed production by range. Japan • We found variation in MASS. phenology between ranges Germinate to Flowering (Figure 2), where time Flowering to Fruiting CT & VT between stages was shortest in the Connecticut and 0 20 40 60 80 100 120 140 Mean # Days Between Stages Vermont populations (total Figure 2: Mean time between each life cycle stage. life-cycle <3 months), but was almost 3 times longer in European, Massachusetts, and Japanese populations (total life-cycle 5-7 months). 1: Greenhouse: • Are there different life histories between ranges? Worldwide seed collection: How do invasive counterparts? 75 Europe Comparing invasive genotypes to native counterparts Cardamine hirsuta (hairy bittercress) A USA Research Questions: • Brassica family • Germinates year-round, can over-winter • Life cycle 2.5 to 7 months • Plants self fertilize • Native to Europe, weedy in USA, invasive in Japan Summary: 100 Fecundity Matthew A. Kaproth University of Vermont, Department of Plant Biology Seed to Germinate Results: Field Common Garden • Germination rates were lower in the European genotypes than in the invasive Japanese and USA genotypes (Figure 3), and 8.8-10.0 times lower in undisturbed plots. • Rates of flowering were much lower in the European genotypes than in the invasive Japanese and USA genotypes (Figure 4). Japanese plants were delayed in development. Flowering was highest in plots with heavy to mild disturbance. • Rates of seed pod production, maturity, and fecundity were highest in the Japanese and USA genotypes (Figure 5), and under heavy disturbance. Amount of seeds per pod were double in plots with low initial planting density. Are there differences in how genotypes from different ranges respond to competition and disturbance? • Genotypes respond equally to competition – only the number of seeds per seed pod was modified by initial planting density • Disturbance enhances establishing population development (heavy disturbance increases fecundity and germination as well). Future work to compare life history traits (and dispersal) of global collection under varying competition densities in a greenhouse common garden. 1 plant • After 12 weeks, the rate of new germinants (2nd generation) was highest in USA genotypes, and under heavy disturbance. 5 plants VT:E 60 A Japan Malta 50 A 40 A 30 20 B 10 0 0 10 20 30 0.7 VT:C VT:E 0.6 Japan Malta 0.5 0.4 A 0.3 A 0.2 0.1 B 0 40 40 50 60 Figure 3: Germination and survivorship 1m Mild 10 cm Heavy Population Growth (λ) Disturbance Intact ? 10 10 50 # Seeds Planted 250 50 # Seeds Planted 250 A USA 9 Malta 8 Japan 7 10 plants 6 5 4 A 3 2 B 1 0 40 50 60 70 # of Days Sown Figure 4: Rate of flowering Methods: Greenhouse study: Collected seeds individually grown in a controlled environment. Differences in phenology and fecundity between ranges (and genotypes nested within ranges) were analyzed using ANOVA (see top center white panel). Field experiment: Investigated life history traits under varying levels of disturbance and planting density (see neighboring blue panel). 70 # of Days Sown # of Days Sown 10 A Rate of Seed Pods Produced Flowering Rate (per planted seed) VT:C % Alive • USA: 5 weedy / introduced populations: Connecticut, Massachusetts & Vermont • Europe: 2 native populations: France, Malta • Japan: 8 invasive/introduced populations: Range from Yamaguchi through Utsunomiya 70 Figure 5: Seed Pod Production 3 levels of disturbance and propagule pressure (replicates randomized) • Seeded April 2010 • Seed ranges: USA (Vermont) Europe (Malta) Japan (Chiba) Literature Cited: Grotkopp, E., M. Rejmánek, and T. L. Rost, 2002. Toward a causal explanation of plant invasiveness: Seedling growth and life-history strategies of 29 pine (Pinus) species. Am. Nat. 159:396-419. Richardson, D.M. and M. Rejmánek, 2004. Conifers as invasive aliens: a global survey and predictive framework. Diversity and Distributions 10(5-6): 321 - 331. Funded by USDA-NRI 20006-03645, USDA-Hatch to J.M. and Grant-InAid of Research from Sigma Xi to M.A. Kaproth. Thank you to J. Allen, R. Bertin, B. Connolly, A. DeSenna, M. Eppinga, E. Imbert, H. Kudoh, T. Nishio, L. Schmitt, and S. Strella.