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Variable responses of natural enemies to Salix triandra phenotypes with different secondary chemistry
Author(s) -
Hjältén Joakim,
Niemi Lena,
Wennström Anders,
Ericson Lars,
Roininen Heikki,
JulkunenTiitto Riitta
Publication year - 2007
Publication title -
oikos
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.672
H-Index - 179
eISSN - 1600-0706
pISSN - 0030-1299
DOI - 10.1111/j.0030-1299.2007.15365.x
Subject(s) - sawfly , biology , willow , gall , rust (programming language) , phenotype , natural population growth , population , botany , resistance (ecology) , herbivore , natural selection , phenotypic trait , defence mechanisms , salicaceae , phenotypic plasticity , woody plant , ecology , gene , hymenoptera , genetics , demography , sociology , computer science , programming language
Plant phenotypes often differ in their resistance to natural enemies, but the mechanism for this has seldom been identified. The aim of this study was to determine if the spatial patterns of phenotype use of a highly specialized insect herbivore (the galling sawfly Pontania triandrae ) in a natural willow population can be related to phenotypic variation in plant secondary chemistry. Furthermore, we tested if traits that confer resistance to one type of natural enemy, i.e. the galling sawfly, also confer resistance to others, in our case a leaf beetle Gonioctena linnaeana and the rust fungus Melampsora amygdalinae . We identified 18 phenotypes with high and 18 phenotypes with low gall density in our field population and determined gall densities, the degree of leaf damage and rust infection on each phenotype and collected leaves for chemical analyses. The concentration of phenolics was higher in phenotypes with high density of galls suggesting that this galling sawfly may use phenolics as oviposition cues. Rust infection showed the opposite pattern, with lower levels on clones with high concentration of phenolics, while leaf damage by G. linnaeana did not differ between clone types. This indicates that these important natural enemies may assert divergent selection on willow phenotypes and that this might provide a mechanism for maintaining phenotypic variation within willow populations.