Print PageThe dispersal of a plant species into a novel range may be accompanied by evolution of the invader. The amount of genetic variation present across the invaded range will determine whether smaller populations are able adapt to local conditions or to evolve into more aggressive invaders. The invasive species Ailanthus altissima has a latitudinal cline in flowering phenology across Europe, for example, and species including Silene latifolia and Sapium sebiferum trade off faster growth rates for weaker defenses against herbivory in their invaded range. We collected seeds from 13 populations (90 seed families) of the invasive tree Ailanthus altissima from the invaded range in eastern North America, and planted them in a common garden in Tennessee. A pilot study of three populations suggested that the populations have distinct phenotypes for measures of performance such as plant height and biomass production. We hypothesized that 1) we would see evidence of a latitudinal cline particularly in phenology, and 2) that there would be tradeoffs between growth and susceptibility to herbivory across the range.
Results/Conclusions
Initial analyses show that there is a weakly significant effect of population on timing of bud break time in the spring, and a significant effect of family on spring leaf out. However, these genetically-based differences in phenology do not vary according to the latitude of their parental population. Latitude of parental population also has no predictive power for plant height, herbivory, or disease across the two years of the experiment. There are strong effects of population on plant height in the first year of growth, but not in the second year of growth. Similarly, there are strong effects of population on the amount of damage caused by herbivores and disease only in the first year of growth. However, there is no correlation between herbivory and plant height in the first year of growth, and only a very weak negative correlation between disease and plant height in the first year. Our results do not support our hypotheses that genetic variation in Ailanthus altissima follows either latitudinal or defense tradeoff patterns of adaptation. We do see strong patterns of between- and within-population genetic variation in plant height, herbivory, and disease, suggesting that populations are genetically distinct for important performance traits, even if there is no larger pattern of adaptation across this part of their range.
