As part of the “Tansley Medal” competition of the journal New Phytologist, I was asked to write a short (max 2500 words) Tansley Insight article. I applied for the competition a year ago, and was informed last April that I was short-listed. This pushed me to finally write this review, of which the topic dates from my PhD times.
I did my PhD at the University of Zurich as part of the ‘Cenozoic Angiosperm Radiation’ (CAR) project led by Prof. Peter Linder (who recently retired). The CAR team included several people, among them Colin Hughes, Yaowu Xing, Yanis Bouchenak-Khelladi and Erik Koenen. We would have Tuesday afternoon beers for several years to discuss ideas and projects. The main aim was to understand angiosperm radiations from phylogenies, fossils and functional traits, and we managed to tackle this question in several angiosperm clades, such as Fagales, Rhamnaceae, Proteaceae and Ericaceae. The emergent patterns across clades showed that radiations, or evolutionary diversification, is often the result of the intricate interaction between traits and environments.
What remained an unanswered question, to me at least, was why angiosperms seem to have managed to radiate much more than other plant clades, such as gymnosperms, and also why not all angiosperm clades do equally well (in terms of their diversification rate). This question is not new, it was already proposed by Darwin (his second ‘abominable mystery’) and reviewed by Crepet and Niklas in 2009.
What I propose in my review, is that angiosperms (compared with gymnosperms) and species-rich angiosperm lineages (compared with species-poor lineages) have had (1) many trait innovations, (2) many ecological opportunities that emerged during Cenozoic global changes and (3) ‘trait flexibility’ to explore the functional space of novel traits, allowing for rapid adaptation to novel environments. These three ‘ingredients’ combined could lead to increased diversification rates. I quantified the support for this idea by performing a systematic review across the literature for trait-dependent diversification rates (key innovations) and trait transition rates (trait flexibility). Indeed, it seems that although no trait consistently leads to radiation across angiosperms, certain lineages may be predisposed to evolve the right traits in the right place at the right time, suggesting trait flexibility. This may have a genetic basis, and may explain why angiosperms have risen to dominance in most terrestrial ecosystems during the Cenozoic (i.e., the last 66 million years).
Hopefully it’s good enough to win the Tansley Medal.
Onstein, RE (in press). “Darwin’s second ‘abominable mystery’: trait flexibility as the innovation leading to angiosperm diversity” New Phytologist. [ABSTRACT].