Defining invasiveness and its inheritance using growth and reproductive traits of an invasive grass

Background/Question/Methods

Phenotypic plasticity (inherited and non-inherited) is a key mechanism of invasiveness and, if inherited, could explain rapid adaptation to novel environments of some nonnative plants. Measuring growth and reproductive traits of parent plants from different environments and comparing these traits to those of their offspring grown in a common environment enables us to evaluate inheritance of plastic traits. Microstegium vimineum, an invasive grass, exhibits plastic growth and reproductive responses to variable light conditions and different flowering phenologies across latitudes and longitudes. Our goal was to determine if these traits were heritable at local and regional scales. Plants and seeds were collected from populations at riparian and southwest-facing slope/ridge paired-habitats in MD, OH, PA, VA, and WV. Field-collected progeny were grown under shared controlled greenhouse conditions. Traits measured that compare both parent and progeny included measures of the tallest tiller (apical and basal internode length difference divided by node count (A-B/N) or divided by height (A-B/H)), leaf length and width ratio for apical and mid-tallest tiller leaves (A_L/W and M_L/W), and floret weight. Shoot biomass, tiller number, days-to-first flower, germination rate, and inflorescence-biomass to shoot-biomass ratio (RepVeg) of the progeny were measured and compared with latitude, longitude, and elevation of the parent populations. Traits were evaluated across population, habitat, latitude, longitude, and elevation using generalized linear models, nonparametric tests, and regression analyses.

Results/Conclusions

Both progeny and parent populations differed for A-B/N and A-B/H with the OH progeny population having the highest A-B/H and several WV parent populations having the lowest A-B/N values. Floret weight differed among progeny populations with one WV population having the heaviest florets. Parent populations showed no difference in floret weight, though the same WV population’s florets weighed the least. A_L/W did not differ in the progeny but did so for the parents with VA having larger values than OH and one WV population. In contrast, M_L/W differed only for the progeny with OH plants having the smallest values. Increasing longitude was correlated with increasing A-B/H and increasing RepVeg was correlated with decreasing longitude and elevation. Floret weight, days-to-first flower, and germination rate increased with increasing elevation. Thus, the traits measured differed between parents and progeny, supporting phenotypic plasticity without inheritance. Correlations of one vegetative and several reproductive traits of the progeny with longitude and elevation support trait inheritance or reflect maternal effects. We plan transgenerational experiments to distinguish between heritability and maternal effects.