Some animal-pollinated plants face an interesting dilemma. The same animals they rely on for pollination also like to eat them. This is the case for Nicotiana attenuata, a wild tobacco plant that grows in the American Southwest. The plant is pollinated by the night-active hawkmoth, which after the quib pro quo exchange of pollination for nectar likes to lay its eggs on N. attenuata—eggs that develop into voracious, leaf-eating caterpillars.

But N. attenuata has an interesting trick up its sleeve, say the authors of a new study in Current Biology. Stimulated by oral secretions released by the munching caterpillars, the tobacco plant performs an astonishing change in flower phenology in which the flowers open in the morning instead of at night.

This change in flower phenology, as well as other alterations, including a metamorphosis in flower shape and the loss of key chemical attractants, leads to a switch in pollinators from the hawkmoth to a local hummingbird. The latter, unlike the hawkmoth, is normally active during the day and seems to be satisfied with just a nectar treat.

Of course, these observations raise the question of why N. attenuata bothers producing night-opening flowers that attract hawkmoths in the first place. Why not just focus on luring hummingbirds? Baldwin and colleagues don't know the answer to this question, but it's possible that the hawkmoth, for all its faults, might be a more reliable and effective pollinator than the hummingbird.

Looking to the field of plant-pollinator interactions more generally, the findings have some potentially broad implications. For one, plants face another dilemma, related to the one described by the researchers, in which traits that attract a pollinator can also attract herbivores, resulting in an inevitable trade-off.

Thus, one wonders whether herbivore-induced changes to flower phenology could be used more generally to mitigate the unwanted side effects associated with flowers that are attractive to both pollinators and herbivores.

 By studying how the caterpillars' oral secretions induce the switch in flower phenology, the team also discovered that a chemical pathway crucial to many defense responses in plants is required. The role of such a common defense pathway raises the interesting possibility that the effects of herbivore attack described in the study may be common in plants.

Taken as a whole, the findings highlight the remarkable adaptability of plants to changing circumstances and the complex, sometimes contentious, relationships between plants and their pollinators.



Citation: Danny Kessler, Celia Diezel, Ian T. Baldwin, 'Changing Pollinators as a Means of Escaping Herbivores', Current Biology, January 2010; doi:10.1016/j.cub.2009.11.071