Does variation in defensive secondary metabolites in native and non-native Lonicera species explain invasive success? Responses to nutrient availability and relationships with herbivore resistance in a common garden experiment

Background/Question/Methods

The genus Lonicera (Caprifoliaceae) includes approximately 200 species worldwide, with 18 native and 16 introduced species in North America. Several Asiatic Lonicera species have become some of most problematic woody plant invasives in the United States (e.g., L. maackii, L. tatarica, and L. japonica), while native Lonicera species, (e.g., L. reticulata, L. dioica, and L. flava) are relatively uncommon across their native range. Several phenolic metabolites and iridoids produced by Lonicera species exhibit allelopathic and anti-herbivore effects. In an effort to distinguish species-specific differences in chemical profiles, we examined the phenolic and iridoid glycoside profiles of 4 native (L. reticulata, L. hirsuta, L. sempervirens, and L. flava) and 5 non-native (L. maackii, L. japonica, L. tatarica, L. fragrantissima, and L. xylosteum) Lonicera species and the native confamilial, Diervilla lonicera grown in a common garden experiment in the field. Extracts were made from leaves collected from fertilized and unfertilized plants of each species in August 2012 and samples were analyzed using HPLC for phenolics and GC-MS for iridoids. We also compared the laboratory performance of the generalist caterpillar (Spodoptera frugiperda) fed leaves of native and exotic Lonicera species (2 native, 3 non-native) grown in the same common garden. 

Results/Conclusions

The non-native Lonicera species were characterized by having higher concentrations of phenolic compounds (chlorogenic acid, luteolin, luteolin-7-glucoside, and apigenin), variable responses to fertilization, and reduced total iridoid glycoside content and number of identified iridoid glycosides. Total iridoid glycoside content and the number of identified iridoid glycosides were higher in fertilized native Lonicera species with the highest values found in L. flava. Performance of S. frugiperda larvae was poorest on unfertilized plants, which correlated with higher levels of some metabolites, and larvae did not survive at all on leaves of unfertilized L. maackii, L. reticulata, and L. sempervirens. Relative growth rates were highest for larvae feeding on non-native L. tatarica and L. fragrantissima. Continuing analysis will include multivariate approaches to separate defense profiles by species, to determine the presence of unique compounds within species, and to determine the relationships between defense metabolites, environmental variation, and herbivore performance.