Lonicera X bella: The permutations of plasticity in an invasive shrub

Lonicera x bella, the hybrid of L. morrowii and L. tatarica, is a tremendously invasive species throughout most of the northeastern U.S. and adjacent Canada. It is highly dispersible and thrives in a range of light environments. We asked whether the success of L. X bella in sun and shade habitats was attributable to phenotypic plasticity among a putative genetically diverse sample of hybrids, or might be a species characteristic represented in all hybrids. Seeds of 20 maternal genotypes were gathered from naturalized populations (northern Wisconsin and northeastern Illinois), cold stratified, and germinated under greenhouse conditions. Seedlings were transferred to sun and shade treatments at 12 weeks of age in a randomized complete block design. Morphological characteristics related to growth and fitness were compared at 21 weeks of age. Analysis of variance revealed large treatment effects (plasticity) and maternal genotype responses for leaf numbers, total weights, leaf weight, above & below ground biomass, root weight, stem weights and leaf: root ratio. Surprisingly, no phenotypic plasticity (maternal genotype x treatment interaction) was detected in any trait. Apparently a generalized phenotypic response is present among all genotypes, although there are clear performance differentials among the progeny of various mothers.