Bryant is the author of today's entry.
Today's images of Nicotiana attenuata (commonly known as coyote tobacco) were generously contributed by Danny Kessler, who researches this incredible species. Nicotiana attenuata may not appear extraordinary at first glance, but this species exhibits a number of remarkable responses to predation. Hawk moths (Manduca spp.) are both friends and foes to coyote tobacco. The adult moths are common nocturnal pollinators for this species, but the larvae (aka tobacco hornworm) are one of this plant's main predators. When a plant of coyote tobacco is subjected to the oral secretions produced by feeding hawk moth larvae, a chemical signal (jasmonic acid) is released into the air. This signal is picked up by the same individual and triggers a dramatic change in the individual's phenology. It does so rather dramatically, by switching from producing flowers that open at night (and hence attracting the hawk moth) to producing flowers that open during the day (which instead attract hummingbirds).
The figure above shows a timescale of morning opening flowers (MoF) and night opening flowers (NoF) with the black blocks representing darkness. The top photograph above shows the NoF on the left and the MoF on the right, taken at 8:00 a.m. when the NoF is still open but about to close, and the MoF is still closed but about to open. The third image shows the same pair of flowers from a top view (NoF on the right this time and MoF on the left).
In addition to changing the flower opening time, the plant will also alter the floral scents it emits, the nectar produced and the morphology of the flower! Once this switch has occurred in the plant, the number of hawk moth visitors significantly declines while the number of hummingbird visitors increases. This decline in hawk moth visitors results in a reduction in eggs that are deposited by hawk moths, thereby reducing future predation by hawk moth larvae. Pollination continues to successfully occur via hummingbirds.
This particular response is only elicited when a caterpillar of Manducca spp. begins to feed on the leaves of Nicotiana attenuata, however there are many other herbivorous predators that feed on this species. Switching pollinators is just one of many defenses in this species' arsenal. In fact, Nicotiana attenuata is somewhat of a master of chemical warfare. Its trichomes imbue feasting insects with a chemical scent that attracts insectivorous predators to come have a feast of their own. Also, as you may have guessed, this plant contains the toxin nicotine, which is harmful to virtually all other herbaceous predators (besides the hornworm) with muscle tissues, insects and smokers alike.
The keen observations made by researchers Dr. Ian Baldwin, Danny Kessler and Celia Diezel have elucidated the complex chemical and physical responses that occur when Nicotiana attenuata is predated by hawk moth larvae. But the question remains, why doesn't this species always produce morning opening flowers, and forego its interaction with the hawk moth altogether? There are a number of speculative hypotheses regarding this question but none have been proven.
For a detailed account of the research and findings conducted by Dr. Ian Baldwin and his colleagues see their paper: Baldwin, I.T. et al. 2010. Changing pollinators by Means of Escaping Herbivores. Current Biology. 20(3):237-242.
Professor Ian Baldwin and his colleagues are also featured in a recent documentary, Smarty Plants: Uncovering the Secret World of Plant Behaviour (an episode of The Nature of Things). The section on Nicotiana attenuata is around the 14 minute mark.