DOI: 10.5061/dryad.73n5tb2sx
title: Chemical variations in Quercus pollen as a tool for taxonomic identification: implications for long-term ecological and biogeographical research

description: Aim  Fossil pollen is an important tool for understanding
 biogeographic patterns in the past, but the taxonomic resolution of the
 fossil-pollen record may be limited to genus or even family level.
 Chemical analysis of pollen grains has the potential to increase the
 taxonomic resolution of pollen, but present-day chemical variability is
 poorly understood. This study aims to investigate whether a phylogenetic
 signal is present in the chemical variations
 of Quercus L. pollen and to assess the prospects of
 chemical techniques for identification in biogeographic research.
 Location  Portugal Taxon  Six taxa (five species, one
 subspecies) of Quercus L., Q. faginea, Q.
 robur, Q. robur ssp. estremadurensis, Q. coccifera, Q.
 rotundifolia and Q. suber belonging to three
 sections: Cerris, Ilex, and Quercus (Denk,
 Grimm, Manos, Deng, & Hipp, 2017) Methods  We collected
 pollen samples from 297 individual Quercus trees across
 a 4° (∼450 km) latitudinal gradient and determined chemical differences
 using Fourier-transform infrared spectroscopy (FTIR). We used canonical
 powered partial least-squares regression (CPPLS) and discriminant analysis
 to describe within- and between-species chemical variability.
 Results  We find clear differences in the FTIR spectra
 from Quercus pollen at the section level (Cerris:
 ∼98%; Ilex: ∼100%; Quercus: ∼97%). Successful
 discrimination is based on spectral signals related to lipids and
 sporopollenins. However, discrimination of species within
 individual Quercus sections is more difficult: overall,
 species recall is ∼76% and species misidentifications within sections lie
 between 18% and 31% of the test-set. Main Conclusions  Our
 results demonstrate that subgenus level differentiation
 of Quercus pollen is possible using FTIR methods, with
 successful classification at the section level. This indicates that
 operator-independent FTIR approaches can surpass traditional morphological
 techniques using the light microscope. Our results have implications both
 for providing new insights into past colonisation pathways
 of Quercus, and likewise for forecasting future responses to
 climate change. However, before FTIR techniques can be applied more
 broadly across palaeoecology and biogeography, our results also highlight
 a number of research challenges that still need to be addressed, including
 developing sporopollenin-specific taxonomic discriminators and determining
 a more complete understanding of the effects of environmental variation on
 pollen-chemical signatures in Quercus.
description: This dataset was collected in the spring of 2018, and FTIR
 spectra were recorded using a Vertex 70 FTIR spectrometer (Bruker Optik
 GmbH) with a single reflectance-attenuated total-reflectance (SR-ATR)
 accessory in Summer 2018. The raw spectra is included
 in the dataset and all preprocessing is documented in separate
 R-files. Preprocessing consisted of 2nd derivate
 calculation using Savitzky Golay and extended multiplicative signal
 correction.