Global Succulent Biome phylogenetic conservatism across the pantropical Caesalpinia Group (Leguminosae)

Abstract

Summary The extent to which phylogenetic biome conservatism vs biome shifting determines global patterns of biodiversity remains poorly understood. To address this question, we investigated the biogeography and trajectories of biome and growth form evolution across the Caesalpinia Group (Leguminosae), a clade of 225 species of trees, shrubs and lianas distributed across the Rainforest, Succulent, Temperate and Savanna Biomes. We focused especially on the little‐known Succulent Biome, an assemblage of succulent‐rich, grass‐poor, seasonally dry tropical vegetation distributed disjunctly across the Neotropics, Africa, Arabia and Madagascar. We reconstructed a time‐calibrated phylogeny, assembled species occurrence data and assigned species to areas, biomes and growth forms. These data are used to estimate the frequency of transcontinental disjunctions, biome shifts and evolutionary transitions between growth forms and test for phylogenetic biome conservatism and correlated evolution of growth forms and biome shifts. We uncovered a pattern of strong phylogenetic Succulent Biome conservatism. We showed that transcontinental disjunctions confined within the Succulent Biome are frequent and that biome shifts to the Savanna, Rainforest and Temperate Biomes are infrequent and closely associated with shifts in plant growth forms. Our results suggest that the Succulent Biome comprises an ecologically constrained evolutionary arena spanning large geographical disjunctions across the tropics.

Biomes as evolutionary arenas: Convergence and conservatism in the trans‐continental succulent biome

“…Rain forests, in contrast, receive year‐round precipitation, have few grasses, and do not experience fire (Eiserhardt et al, 2017). However, a third major lowland tropical biome, the seasonally dry, drought‐deciduous, but grass‐poor and fire‐free vegetation referred to as the succulent biome sensu Schrire, Lavin, and Lewis, 2005, has been recognized (Dexter et al, 2018; Gagnon, Ringelberg, Bruneau, Lewis, & Hughes, 2019; Lavin et al, 2004; Oliveira‐Filho et al, 2013; Schrire et al, 2005), but remains little known, lacks a quantitative distribution map, and is often neglected.…”

Joint phylogenetic estimation of geographic movements and biome shifts during the global diversification ofViburnum

“…This is because they necessitate, at least: (1) a compelling phylogenetic analysis of a comprehensive sample of relevant species (a phylogenetic component); (2) the incorporation of fossils to assess the absolute timing of events (a temporal component); (3) a historical biogeographic analysis that identifies and explains geographic disjunctions (a spatial component); and (4) information on the environments occupied by the species under consideration (an ecological component). Using quantitative phylogenetic models, numerous recent studies have extracted important insights from the comparison of dated phylogenies, geographic inferences, and biome reconstructions (e.g., Weeks et al, 2014;Meseguer et al, 2015;Cardillo et al, 2017;Gagnon et al, 2019). On the whole, analyses of these components have been carried out sequentially: species relationships are first inferred from sequence data, the tree is then time-calibrated with fossils, and the dated tree is used to separately infer geographic movements and biome shifts during the evolution of a clade.…”

Adaptation meets dispersal: legumes in the land of succulents

“…I cannot resist one last irony highlighted by Gagnon et al . (), namely that a succulent biome full of legumes may have existed long before succulents themselves joined the party. The Caesalpinia clade was radiating, presumably in scattered dry environments, way back in the Eocene, but the major clades of succulent plants did not come on the scene until the Miocene (Arakaki et al ., ).…”