J Syst Evol ›› 2021, Vol. 59 ›› Issue (4): 776-790.DOI: 10.1111/jse.12730

• Research Articles • Previous Articles     Next Articles

Macroevolutionary insights into sedges (Carex: Cyperaceae): The effects of rapid chromosome number evolution on lineage diversification

José I. Márquez‐Corro1*, Santiago Martín‐Bravo1, Pedro Jiménez‐Mejías2, Andrew L. Hipp3,4, Daniel Spalink5, Robert F. C. Naczi6, Eric H. Roalson7, Modesto Luceño1, and Marcial Escudero8   

  1. 1Department of Molecular Biology and Biochemical Engineering, Universidad Pablo de Olavide, Carretera de Utrera km 1, Seville ES 41013, Spain
    2Departamento de Biología (Botánica), Facultad de Ciencias Biológicas, Universidad Autónoma de Madrid, c/Darwin 2, Madrid 28049, Spain
    3The Morton Arboretum, 4100 Illinois Route 53, Lisle, IL 60532, USA
    4The Field Museum, Integrative Research Center, 1400S Lake Shore Dr, Chicago, IL 60605, USA
    5Department of Ecology and Conservation Biology, Texas A&M University, College Station, TX 77843, USA
    6New York Botanical Garden, 2900 Southern Boulevard, Bronx, NY 10458‐5126, USA
    7School of Biological Sciences, Washington State University, Pullman, WA 99164‐4236, USA
    8Department of Plant Biology and Ecology, University of Seville, Reina Mercedes sn, Seville ES 41012, Spain
  • Received:2020-08-24 Accepted:2021-01-21 Online:2021-01-31 Published:2021-07-01

Abstract: Changes in holocentric chromosome number due to fission and fusion have direct and immediate effects on genome structure and recombination rates. These, in turn, may influence ecology and evolutionary trajectories profoundly. Sedges of the genus Carex (Cyperaceae) comprise ca. 2000 species with holocentric chromosomes. The genus exhibits a phenomenal range in the chromosome number (2n = 10 − 132) with almost not polyploidy. In this study, we integrated the most comprehensive cytogenetic and phylogenetic data for sedges with associated climatic and morphological data to investigate the hypothesis that high recombination rates are selected when evolutionary innovation is required, using chromosome number evolution as a proxy for recombination rate. We evaluated Ornstein–Uhlenbeck models to infer shifts in chromosome number equilibrium and selective regime. We also tested the relationship between chromosome number and diversification rates. Our analyses demonstrate significant correlations between morphology and climatic niche and chromosome number in Carex. Nevertheless, the amount of chromosomal variation that we are able to explain is very small. We recognized a large number of shifts in mean chromosome number, but a significantly lower number in climatic niche and morphology. We also detected a peak in diversification rates near intermediate recombination rates. In combination, these analyses point toward the importance of chromosome evolution to the evolutionary history of Carex. Our work suggests that the effect of chromosome evolution on recombination rates, not just on reproductive isolation, may be central to the evolutionary history of sedges.

Key words: BAYOU, bioclimatic variables, Brownian motion, diversification, morphological characters, Ornstein–Uhlenbeck model, Phylogenetic Comparative Methods, QuaSSE, SLOUCH