Report on the working group: Inducible defense and environmental tolerance: a model system for the evolution of phenotypic plastic responses.
April 4-8, 2001

Active Participants:
Wilfried Gabriel, Barney Luttbeg, Andrew Sih, Ralph Tollrian

Subject: "Evolution of reversible plastic responses"

Many inducible defenses are reversible. The time span needed to build up a defense and to switch back to the undefended state might be very short for behavioral responses, but relatively long for morphological changes. In addition, the cue to induce a defense can be reliable or unreliable. Only with complete information can defenses perfectly match the current environment, but incomplete information can be used to adapt for example to the expected averaged predation risk. The concept of environmental tolerance with additional plasticity in the mode and in the breadth of adaptation can be used as a framework to address problems of reversible inducible defenses - and even more generally to model various kinds of reversible plastic responses.

We discussed in detail the results of a model on reversible plasticity that was developed during a six month sabbatical of WG at NCEAS. The model predicts changes in the mode and the breadth of adaptation depending on the coefficient of variation of the environment, the time span for performing shifts in characters, the time period for which such shifts are advantageous, and on the completeness of information. Plasticity in the mode is favorable but there seems to be always strong selection pressure to evolve plasticity in mode and breadth.

The main goal of this workshop was to prepare a publication of the model and its results. Before the start of the working group the Appendix and the Method section had been written with many figures to demonstrate the main results. All formulas where available in a "Mathematica"-file so that we could easily produce new figures and study the impact of any model parameter. We decided on the main structure of the paper and on figures to be presented. We started to write the Introduction, the Results, and the Discussion sections, and started to produce the final figures. Roughly 2/3 of a first draft was finished during the working group meeting.

We had an intense discussion - also together with Drew Harwell - on further directions of modeling reversible plastic responses, future possible modifications of the existing model and development of other complementary models. We made first outlines for a second paper that should review reversible plastic responses. We will work on the second paper as soon as the first one is finished.

We agreed that is would be worthwhile to organize a working group that compares inducible defenses in microbiology, plant ecology and animal ecology.