Genetic and environmental aspects of phenotypic plasticity in invasive Lonicera maackii and Lonicera x bella honeysuckles

Background/Question/Methods Two Asiatic shrub honeysuckles, Lonicera maackii and Lonicera x bella, are prominent and troublesome invaders of Midwestern forests. They feature seemingly high levels of phenotypic plasticity in response to light availability. In a previous study we discovered strong genetic and environmental effects on the responses of L. x bella to light availability, but few significant gene x environment responses. Here we compare patterns of response in L. x bella and L. maackii in a small greenhouse experiment involving 8 maternal genotypes of each species. We hypothesized stronger genetic responses in hybrid L. x bella.

Results/Conclusions

Seed germination rates differed significantly between the species (L. maackii 55%, L. x bella 72%), with much greater variability among maternal genotypes of L. maackii (CV = 41% vs. 24%). Seedling heights 40 days after planting (in full light) were significantly greater (230%) for L. maackii, which remained taller (180%) at 80 days. RGR rate did not differ in the 40-80 day growth period. Half of each population was subsequently grown in 60% shade for 27 days. Height growth did not differ across treatments, although height in L. maackii was 130% of L. x bella. Shade treatments caused significant (20%) reductions in RGR across the 80-107 day growth period. RGR was about 15% lower in shaded L. maackii than in L. x bella. In L. x bella maternal and treatment effects were present for height, but only treatment effects were present for RGR. No maternal, treatment or interaction effects were present in the heights of L. maackii at 107 days, although prominent maternal and treatment differences were present for RGR. We conclude that genetic differences may be more important in L. maackii than in hybrid L. x bella, both in terms of seed germination and growth rate. The role of nongenetic maternal effects requires further investigation.