The Second Generation of Hypotheses About Colorful Autumn Leaves

Abstract

The strongest advocate of the defensive role of red and yellow autumn leaf coloration as a case of Zahavi’s handicap principle was Dr. Marco Archetti. After the unexpected death of Professor Bill Hamilton in the year 2000, Marco Archetti was practically left by himself to carry the red/yellow autumn leaf handicap flag. As a Post Doc at Oxford University, he arranged a small conference on the autumn leaf color issue in Oxford’s St. John’s College in March 2008. In that conference, attended by plant physiologists, plant and animal ecologists, and several scientists that specialised in the sensory systems of herbivorous insects, the various and even contrasting views concerning the biology of autumn leaf coloration were presented. Two days of focused discussions vividly illuminated the need for a well-balanced multidisciplinary understanding, and that such a review had to be written and published by the group, and indeed, a year later it was published in Trends in Ecology and Evolution (Archetti et al. 2009a). Among other things, it became clear to all the scientists involved that yellow and red autumn leaves are in a way two different strategies (although not always and not concerning all defensive aspects) and that at least concerning the co-evolutionary hypothesis, they should be treated separately. Moreover, it also became clear that both physiology and ecolgy are involved and that the gains from autumn coloration do not stem from only one of these very different function types, and also that aposematic signaling is involved as well. This understanding was an important step to lower the flames that blazed in the arena of investigating the evolution and functions of colorful autumn leaves, but this critical understanding and even later progress did not eliminate the need for an even better understanding of the complicated scientific question of the evolution of autumn leaf colors.