Wednesday 15. 1. 2019, 12:00, Kokomo room (former library)
Uriel Gelin (XTBG, China): Spinescence: mechanisms of evolutionary history across continents
We live in an era dominated by flowering plants and Mammals (at least for vertebrates): their remarkable diversity mostly results from what has happened in a context of post mass extinction, active plate tectonics and changing climate during the last 66 million years. The diversity of traits results from selective pressure and can then inform us on evolutionary mechanisms. My work has focused on a plant physical defense, spines that are assumed to be a defense against mammalian herbivores. However, this idea mostly results from experiments on a limited number of herbivore species and is strongly biased towards one continent evolutionary history. I aimed at testing: (1) the efficacy of various spinescence patterns on impeding feeding rate of mammal species, using experimental manipulation of plant spines given to captive mammals and (2) the evolutionary history of spinescence, combining state-of-the-art phylogenetic methods with recent advances in our understanding of the evolution of plants. First, we conducted 409 trials (4090 branches) aiming at testing the efficiency of 3 different types of spines (prickles (Rubus), thorns (Crataegus) and leaf spines (Ilex)) on foraging behaviour and plant biomass removal in up to 17 species of mammals of very diverse orders (e.g. wallabies, porcupines, goats, deers, baboons..). Early results clearly showed that spinescence is generally a very efficient defense against mammalian herbivores but also that some type of spines are more efficient than other to prevent leaf removal but this efficiency also depends on the mammal species, suggesting that specific way of foraging have triggered the evolution of different types of spine. To test more specifically the coevolution hypothesis, I summarized the key events that shaped the co-evolution between large Mammals and flowering woody plants, using large dated phylogenies (8127 plant and 356 herbivore species) and extensive fossil records (5592 herbivore species) at world scale. We show that the evolution of a common and diverse plant defense structure (one tenth of species), the spines, was strongly dependent upon continental mammal history but less likely linked to any disclosable global climatic trend nor other class of herbivores. Spinescence is therefore a very useful marker to track how biotic interactions trigger evolution. In support of the behavioural experiments, the type of feeding behaviour selected for various defence types: plants with spines probably not defend against megaherbivores using trunk (elephants) but seemed to have developed stem spines (rose or hawkthorne) mainly against the ones pulling directly leaves with their mouth (antelopes, deers) and leaf spines (holly) as an ultimate defense against the ones using “hand” (kangaroos, ground sloths).