J Syst Evol

• Research Article •    

Phylogenetic diversity and regionalization in the temperate arid zone

Ryan A. Folk1*, Aliasghar A. Maassoumi2, Carolina M. Siniscalchi1, 3, Heather R. Kates4, Douglas E. Soltis4, 5, 6, 7, Pamela S. Soltis4, 6, 7, Michael B. Belitz†4, 3, Robert P. Guralnick†4, 7   

  1. 1. Department of Biological Sciences, Mississippi State University, Mississippi State, MS, USA;
    2. Research Institute of Forests and Rangelands, Tehran, Iran;
    3. University Libraries, Mississippi State University, Mississippi State, MS, USA;
    4. Florida Museum, University of Florida, Gainesville, FL, USA;
    5. Department of Biology, University of Florida, Gainesville, FL, USA;
    6. Genetics Institute, University of Florida, Gainesville, FL, USA;
    7. Biodiversity Institute, University of Florida, Gainesville, FL, USA
    * Author for correspondence:rfolk@biology.msstate.edu
    These authors contributed equally.
  • Received:2023-11-01 Accepted:2024-03-01 Published:2024-04-12

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 challenge. Here we identify the spatial distribution of diversity and endemism in Astragalus, using 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.

Key words: Astragalus, spatial phylogenetics, Iran, phyloregion, biogeography, CANAPE