The complex interaction between megaherbivores, climate and fire has shaped the evolution and distribution of plant spinescence across biogeographical realms (preprint)

Abstract:

The evolutionary arms race between plants and herbivores has led to numerous adaptations in plants, including prickles, thorns, and spines. However, whether spinescence evolved primarily in response to herbivory, or whether abiotic conditions also played a role, remains unknown. We integrated phylogenetic, geographic, and trait data for 1,835 species of an ecologically diverse and spiny pantropical lineage – mimosoid legumes – with data for 235 extant and 185 extinct mammalian herbivores >10 kg. Using structural equation models, we assessed how megaherbivores, climate and fire directly or indirectly affected the proportion of spinescent mimosoids across global and continental assemblages. We detected repeated evolution of spinescence throughout the evolutionary history of mimosoids. The proportion of spinescent mimosoids increased with greater richness of both extant and extinct herbivores, as well as with higher drought intensity and temperatures. Fire influenced spinescence indirectly by affecting megaherbivore richness. Importantly, herbivore richness (both extant and extinct), drought, and temperature were significant determinants of spinescence on both continents. However, in the Americas, the effect of extant herbivore richness was stronger, whereas in Africa, extinct herbivore richness had a comparatively greater influence. We show that large mammals have shaped spinescence in mimosoid legumes, but this happened especially in warm, fire-prone and dry environments, where losing plant parts is particularly costly. Furthermore, the distribution of spines cannot be fully understood without considering past interactions with now extinct megaherbivores, illustrating legacy effects on plant traits.

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Recommended citation: Souza Ferreira, R., Ringelberg, J., Hughes, C., Arle, E., Wölke, F.J.R., Tomlinson, K., Onstein, R.E. (2025), The complex interaction between megaherbivores, climate and fire has shaped the evolution and distribution of plant spinescence across biogeographical realms (preprint)
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