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High species richness and endemism in tropical mountains are recognized as major contributors to the latitudinal diversity gradient. The processes underlying mountain speciation, however, are largely untested. The prevalence of steep ecogeographic gradients and the geographic isolation of populations by topographic features are predicted to promote speciation in mountains. We evaluate these processes in a species-rich Neotropical genus of understory herbs that range from the lowlands to montane forests and have higher species richness in topographically complex regions. We ask whether climatic niche divergence, geographic isolation, and pollination shifts differ between mountain-influenced and lowland Amazonian sister pairs inferred from a 756-gene phylogeny. Neotropical Costus ancestors diverged in Central America during a period of mountain formation in the last 3 My with later colonization of Amazonia. Although climatic divergence, geographic isolation, and pollination shifts are prevalent in general, these factors don’t differ between mountain-influenced and Amazonian sister pairs. Despite higher climatic niche and species diversity in the mountains, speciation modes in Costus appear similar across regions. Thus, greater species richness in tropical mountains may reflect differences in colonization history, diversification rates, or the prevalence of rapidly evolving plant life forms, rather than differences in speciation mode.
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The rapid radiation of Bomarea (Alstroemeriaceae: Liliales), driven by the rise of the Andes
Abstract Geological events such as mountain uplift affect how, when, and where species diversify, but measuring those effects is a longstanding challenge. Andean orogeny impacted the evolution of regional biota by creating barriers to gene flow, opening new habitats, and changing local climate. Bomarea (Alstroemeriaceae) are tropical plants with (often) small, isolated ranges; in total, Bomarea species occur from central Mexico to central Chile. This genus appears to have evolved rapidly and quite recently, and rapid radiations are often challenging to resolve with traditional phylogenetic inference. In this study, we apply phylogenomics—with hundreds of loci, gene-tree-based data curation, and a multispecies-coalescent approach—to infer the phylogeny of Bomarea. We use this phylogeny to untangle the potential drivers of diversification and biogeographic history. In particular, we test if Andean orogeny contributed to the diversification of Bomarea. We find that Bomarea originated in the central Andes during the mid-Miocene, then spread north, following the trajectory of mountain uplift. Furthermore, Andean lineages diversified faster than non-Andean relatives. Bomarea thus demonstrates that—at least in some cases—geological change rather than environmental stability has driven high species diversity in a tropical biodiversity hotspot. These results also demonstrate the utility (and danger) of genome-scale data for making macroevolutionary inferences.
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- PAR ID:
- 10489026
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Evolution
- Volume:
- 78
- Issue:
- 2
- ISSN:
- 0014-3820
- Format(s):
- Medium: X Size: p. 221-236
- Size(s):
- p. 221-236
- Sponsoring Org:
- National Science Foundation
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