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Abstract AimQuantifying the phylogenetic diversity of temperate trees is essential for understanding the processes that have shaped the modern distribution of temperate broadleaf forest and other major forest biomes. Here, we focus on Fagales, an iconic member of forests worldwide, to uncover global diversity and endemism patterns and investigate the distribution of root nodule symbiosis (RNS), an important morphological specialisation in this clade, as a key factor behind these patterns. LocationGlobal. TaxonFagales. MethodsWe combined phylogenetic data covering 60.2% of living species, fine‐scale distribution models covering 90% of species, and nodulation data covering all species to investigate the distribution of species richness and phylogenetic diversity at fine spatial scales compared to the distribution of RNS. We identify abiotic environmental factors associated with RNS and with Fagales diversity in general. ResultsWe find the highest species richness in temperate east Asia, eastern North America, and equatorial montane regions of Asia and Central America. By contrast, relative phylogenetic diversity (RPD) is highest at higher latitudes, where RNS also predominates. We found a strong spatial structuring of regionalisations of Fagales floras, reflecting distinct Northern and Southern Hemisphere floras (except a unique Afro‐Boreal region), each with distinct RNS‐environment relationships. Main ConclusionsAlthough species richness and phylogenetic regionalisation for Fagales accord well with traditional biogeographic concepts for temperate forests, this is not the case for RPD. RNS is almost universal in the highest RPD regions, which may reflect ecological filtering promoting RNS in these regions. Our results highlight the utility of global‐scale, clade‐specific spatial phylogenetics and its utility for understanding drivers of diversity in species‐rich clades.
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Phylogenetic diversity and regionalization in the temperate arid zone
Abstract Astragalus(Fabaceae) is astoundingly diverse in temperate, cold arid regions of Earth, positioning this group as a model clade for investigating the distribution of plant diversity in the face of environmental challenges. Here, we identify the spatial distribution of diversity and endemism inAstragalususing species distribution models for 752 species and a phylogenetic tree comprising 847 species. We integrated these to map centers of species richness (SR) and relative phylogenetic diversity (RPD) and used randomization approaches to investigate centers of endemism. We also used clustering methods to identify phylogenetic regionalizations. We then assembled predictor variables of current climate conditions to test environmental factors predicting these phylogenetic diversity results, especially temperature and precipitation seasonality. We find that SR centers are distributed globally at temperate middle latitudes in arid regions, but the Mediterranean Basin is the most important center of RPD. Endemism centers also occur globally, but Iran represents a key endemic area with a concentration of both paleo‐ and neoendemism. Phylogenetic regionalization recovered an east‐west gradient in Eurasia and an amphitropical disjunction across North and South America; American phyloregions are overall most closely related to east and central Asia. SR, RPD, and lineage turnover are driven mostly by precipitation and seasonality, but endemism is driven primarily by diurnal temperature variation. Endemism and regionalization results point to western Asia and especially Iran as a biogeographic gateway between Europe and Asia. RPD and endemism highlight the importance of temperature and drought stress in determining plant diversity and endemism centers.
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- Award ID(s):
- 1916632
- PAR ID:
- 10636463
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Systematics and Evolution
- Volume:
- 62
- Issue:
- 6
- ISSN:
- 1674-4918
- Format(s):
- Medium: X Size: p. 1201-1217
- Size(s):
- p. 1201-1217
- Sponsoring Org:
- National Science Foundation
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Abstract PremiseAstragalus(Fabaceae), with more than 3000 species, represents a globally successful radiation of morphologically highly similar species predominant across the northern hemisphere. It has attracted attention from systematists and biogeographers, who have asked what factors might be behind the extraordinary diversity of this important arid‐adapted clade and what sets it apart from close relatives with far less species richness. MethodsHere, for the first time using extensive phylogenetic sampling, we asked whether (1)Astragalusis uniquely characterized by bursts of radiation or whether diversification instead is uniform and no different from closely related taxa. Then we tested whether the species diversity ofAstragalusis attributable specifically to its predilection for (2) cold and arid habitats, (3) particular soils, or to (4) chromosome evolution. Finally, we tested (5) whetherAstragalusoriginated in central Asia as proposed and (6) whether niche evolutionary shifts were subsequently associated with the colonization of other continents. ResultsOur results point to the importance of heterogeneity in the diversification ofAstragalus, with upshifts associated with the earliest divergences but not strongly tied to any abiotic factor or biogeographic regionalization tested here. The only potential correlate with diversification we identified was chromosome number. Biogeographic shifts have a strong association with the abiotic environment and highlight the importance of central Asia as a biogeographic gateway. ConclusionsOur investigation shows the importance of phylogenetic and evolutionary studies of logistically challenging “mega‐radiations.” Our findings reject any simple key innovation behind high diversity and underline the often nuanced, multifactorial processes leading to species‐rich clades.more » « less
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