Mistletoes: a hypothesis concerning morphological and chemical avoidance of herbivory.

Leaves from many misletoe species in Australia strongly resemble those of their hosts. This cryptic mimicry has been hypothesized to be a means of reducing the likelihood of mistletoe herbivory by vertebrates. Leaf Kjeldahl nitrogen contents (a measure of reduced nitrogen and thus amines, amino acids and protein levels) of mistletoes and their hosts were measured on 48 mimetic and nonmimetic host-parasite pairs to evaluate hypotheses concerning the significance of crysis versus noncrypsis. The hypothesis that mistletoes mimicking host leaves should have higher leaf nitrogen levels than their hosts is supported; they may be gaining a selective advantage through crypsis (reduced herbivory). The second hypothesis that mistletoes which do not mimic their hosts should have lower leaf nitrogen levels than their hosts is also supported; they may be gaining a selective advantage through noncrypsis (reduced herbivory resulting from visual advertisement of their reduced nutritional status).