Format: ORAL

Rachel Souza Ferreira1, Colin Hughes2, Eduardo Al3, Jens Ringelberg4, Renske Onstein1,5

1- German Centre for Integrative Biodiversity Research (iDiv) Halle – Jena - Leipzig 2- Institut für Systematische Botanik, University of Zurich, Zürich, ZH, Switzerland 3- Department of Zoology, Tel Aviv University, Tel Aviv, Israel 4- School of GeoSciences, The University of Edinburgh, Edinburgh, Scotland, United Kingdom 5- Naturalis Biodiversity Center, Leiden, the Netherlands

The evolutionary arms race between plants and herbivores has led to many adaptations and counter-adaptations in both groups. Plants possess numerous analogous defense structures, such as thorns and spines, that deter predation from large-bodied herbivorous mammals. However, whether herbivory shaped the evolution and distribution of such traits remains unclear. Here, we use a macroecological approach and hypothesize that the evolution and distribution of plant defense traits (spinescence hereafter) is convergent and was shaped by the interaction with medium- to large-sized (i.e., more than 10kg) mammalian herbivores. We focus on the pantropical mimosoid (Mimosoideae, Fabaceae) lineage, including 2338 species (69% of total). We compiled a database of functional traits on growth form, spinescence, leaves, and fruits for all mimosoids. We integrated the mimosoid data with morphological, phylogenetic, and geographical data for 235 extant and 185 extinct species of medium- to large-sized mammalian herbivores, fire regimes, and climate, and applied phylogenetic and structural equation models to identify direct and indirect drivers of spinescence at global and continental scales. Results illustrate the repeated evolution of spinescence across mimosoids, and we show that the global proportion of spinescent species across broad-scale assemblages is strongly associated with species richness of extant and extinct mammalian herbivores and extended periods of drought, whereas fire affected spinescence indirectly, via effects on herbivore richness. Furthermore, we detected biogeographical differences in drivers of spinescence: Extinct herbivore richness was the most important driver in Africa, whereas extant herbivores explained most of the variation in the Americas. Our findings suggest that the environmental correlates of plant defense traits are scale-dependent and that current ecosystems cannot be properly understood without considering past interactions with megaherbivores. We argue that the complex interaction between climate, fire, and the evolution of mammalian herbivores has influenced the evolution and distribution of plant defense adaptations across tropical realms.