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PeerJ. 2018 Jul 19;6:e5055. doi: 10.7717/peerj.5055. eCollection 2018.

A novel approach to study the morphology and chemistry of pollen in a phylogenetic context, applied to the halophytic taxon Nitraria L.(Nitrariaceae).

Author information

1
University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics (IBED), Amsterdam, The Netherlands.
2
University of Potsdam, Institute of Earth and Environmental Science, Potsdam, Germany.
3
University of Münster, Institute of Geology and Palaeontology, Münster, Germany.
4
Universidad Distrital Francisco José de Caldas, Facultad del Medio Ambiente y Recursos Naturales, Bogotá, Colombia.
5
Key Laboratory of Biogeography and Bioresource in Arid Land, Xinjiang Institute of Ecology and Geography, China Academy of Sciences, Urumqi, China.
6
Gothenburg Global Biodiversity Centre, Göteborg, Sweden.
7
University of Gothenburg, Department of Biological and Environmental Sciences, Göteborg, Sweden.
8
Gothenburg Botanical Garden, Göteborg, Sweden.
9
Harvard University, Department of Organismic and Evolutionary Biology, Cambridge, MA, United States of America.
10
Maastricht University, Maastricht Science Programme, Maastricht, The Netherlands.
11
Université de Rennes, Geosciences Rennes UMR-CNRS, Rennes, France.
#
Contributed equally

Abstract

Nitraria is a halophytic taxon (i.e., adapted to saline environments) that belongs to the plant family Nitrariaceae and is distributed from the Mediterranean, across Asia into the south-eastern tip of Australia. This taxon is thought to have originated in Asia during the Paleogene (66-23 Ma), alongside the proto-Paratethys epicontinental sea. The evolutionary history of Nitraria might hold important clues on the links between climatic and biotic evolution but limited taxonomic documentation of this taxon has thus far hindered this line of research. Here we investigate if the pollen morphology and the chemical composition of the pollen wall are informative of the evolutionary history of Nitraria and could explain if origination along the proto-Paratethys and dispersal to the Tibetan Plateau was simultaneous or a secondary process. To answer these questions, we applied a novel approach consisting of a combination of Fourier Transform Infrared spectroscopy (FTIR), to determine the chemical composition of the pollen wall, and pollen morphological analyses using Light Microscopy (LM) and Scanning Electron Microscopy (SEM). We analysed our data using ordinations (principal components analysis and non-metric multidimensional scaling), and directly mapped it on the Nitrariaceae phylogeny to produce a phylomorphospace and a phylochemospace. Our LM, SEM and FTIR analyses show clear morphological and chemical differences between the sister groups Peganum and Nitraria. Differences in the morphological and chemical characteristics of highland species (Nitraria schoberi, N. sphaerocarpa, N. sibirica and N. tangutorum) and lowland species (Nitraria billardierei and N. retusa) are very subtle, with phylogenetic history appearing to be a more important control on Nitraria pollen than local environmental conditions. Our approach shows a compelling consistency between the chemical and morphological characteristics of the eight studied Nitrariaceae species, and these traits are in agreement with the phylogenetic tree. Taken together, this demonstrates how novel methods for studying fossil pollen can facilitate the evolutionary investigation of living and extinct taxa, and the environments they represent.

KEYWORDS:

Australia; FTIR; LM; Mediterranean; Palynology; Paratethys; SEM; Sporopollenin; Steppe-desert; Tibet

Conflict of interest statement

The authors declare there are no competing interests.

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