Nitrogen concentration and mimicry in some New Zealand mistletoes.

The nitrogen concentration in photosynthetic organs of 41 pairs of mistletoes and their respective hosts was compared and found to be higher (in relation to that of their hosts) in cryptic mistletoes and lower in non-cryptic mistletoes. This supports the hypothesis that crypsis may have evolved as a mechanism for avoiding predation by vertebrate herbivores. There were no consistent differences between the nitrogen concentrations of hosts and mistletoes in trees and larger-leaved shrubs (whether native or introduced). The largest differences between mistletoes and their hosts were found on small-leaved divaricate shrubs (Coprosma ssp., Melicope simplex) where the nitrogen concentrations in cryptic mistletoes (Korthalsella spp.) were significantly higher than in their hosts, but significantly lower in prominent mistletoes (Loranthus micranthus, Tupeia antarctica) which apparently "advertise" their unpalatability. If crypsis in New Zealand mistletoes evolved as a protection against herbivory, then it must have evolved in the absence of mammalian herbivores, and the appropriate selection pressures could have been provided only by moas, extinct ratite birds. Otherwise, alternative explanations, such as differing relationships between water use and nitrogen uptake, must be sought for the observed associations of nitrogen concentration and cryptic mimicry in New Zealand mistletoes.