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Paleotemperature Proxies from Leaf Fossils Reinterpreted in Light of Evolutionary History

Present-day correlations between leaf physiognomic traits (shape and size) and climate are widely used to estimate paleoclimate using fossil floras. For example, leaf-margin analysis estimates paleotemperature using the modern relation of mean annual temperature (MAT) and the site-proportion of unto...

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Autores principales: Little, Stefan A., Kembel, Steven W., Wilf, Peter
Formato: Texto
Lenguaje:English
Publicado: Public Library of Science 2010
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3008682/
https://www.ncbi.nlm.nih.gov/pubmed/21203554
http://dx.doi.org/10.1371/journal.pone.0015161
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author Little, Stefan A.
Kembel, Steven W.
Wilf, Peter
author_facet Little, Stefan A.
Kembel, Steven W.
Wilf, Peter
author_sort Little, Stefan A.
collection PubMed
description Present-day correlations between leaf physiognomic traits (shape and size) and climate are widely used to estimate paleoclimate using fossil floras. For example, leaf-margin analysis estimates paleotemperature using the modern relation of mean annual temperature (MAT) and the site-proportion of untoothed-leaf species (NT). This uniformitarian approach should provide accurate paleoclimate reconstructions under the core assumption that leaf-trait variation principally results from adaptive environmental convergence, and because variation is thus largely independent of phylogeny it should be constant through geologic time. Although much research acknowledges and investigates possible pitfalls in paleoclimate estimation based on leaf physiognomy, the core assumption has never been explicitly tested in a phylogenetic comparative framework. Combining an extant dataset of 21 leaf traits and temperature with a phylogenetic hypothesis for 569 species-site pairs at 17 sites, we found varying amounts of non-random phylogenetic signal in all traits. Phylogenetic vs. standard regressions generally support prevailing ideas that leaf-traits are adaptively responding to temperature, but wider confidence intervals, and shifts in slope and intercept, indicate an overall reduced ability to predict climate precisely due to the non-random phylogenetic signal. Notably, the modern-day relation of proportion of untoothed taxa with mean annual temperature (NT-MAT), central in paleotemperature inference, was greatly modified and reduced, indicating that the modern correlation primarily results from biogeographic history. Importantly, some tooth traits, such as number of teeth, had similar or steeper slopes after taking phylogeny into account, suggesting that leaf teeth display a pattern of exaptive evolution in higher latitudes. This study shows that the assumption of convergence required for precise, quantitative temperature estimates using present-day leaf traits is not supported by empirical evidence, and thus we have very low confidence in previously published, numerical paleotemperature estimates. However, interpreting qualitative changes in paleotemperature remains warranted, given certain conditions such as stratigraphically closely-spaced samples with floristic continuity.
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spelling pubmed-30086822011-01-03 Paleotemperature Proxies from Leaf Fossils Reinterpreted in Light of Evolutionary History Little, Stefan A. Kembel, Steven W. Wilf, Peter PLoS One Research Article Present-day correlations between leaf physiognomic traits (shape and size) and climate are widely used to estimate paleoclimate using fossil floras. For example, leaf-margin analysis estimates paleotemperature using the modern relation of mean annual temperature (MAT) and the site-proportion of untoothed-leaf species (NT). This uniformitarian approach should provide accurate paleoclimate reconstructions under the core assumption that leaf-trait variation principally results from adaptive environmental convergence, and because variation is thus largely independent of phylogeny it should be constant through geologic time. Although much research acknowledges and investigates possible pitfalls in paleoclimate estimation based on leaf physiognomy, the core assumption has never been explicitly tested in a phylogenetic comparative framework. Combining an extant dataset of 21 leaf traits and temperature with a phylogenetic hypothesis for 569 species-site pairs at 17 sites, we found varying amounts of non-random phylogenetic signal in all traits. Phylogenetic vs. standard regressions generally support prevailing ideas that leaf-traits are adaptively responding to temperature, but wider confidence intervals, and shifts in slope and intercept, indicate an overall reduced ability to predict climate precisely due to the non-random phylogenetic signal. Notably, the modern-day relation of proportion of untoothed taxa with mean annual temperature (NT-MAT), central in paleotemperature inference, was greatly modified and reduced, indicating that the modern correlation primarily results from biogeographic history. Importantly, some tooth traits, such as number of teeth, had similar or steeper slopes after taking phylogeny into account, suggesting that leaf teeth display a pattern of exaptive evolution in higher latitudes. This study shows that the assumption of convergence required for precise, quantitative temperature estimates using present-day leaf traits is not supported by empirical evidence, and thus we have very low confidence in previously published, numerical paleotemperature estimates. However, interpreting qualitative changes in paleotemperature remains warranted, given certain conditions such as stratigraphically closely-spaced samples with floristic continuity. Public Library of Science 2010-12-22 /pmc/articles/PMC3008682/ /pubmed/21203554 http://dx.doi.org/10.1371/journal.pone.0015161 Text en Little et al. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.
spellingShingle Research Article
Little, Stefan A.
Kembel, Steven W.
Wilf, Peter
Paleotemperature Proxies from Leaf Fossils Reinterpreted in Light of Evolutionary History
title Paleotemperature Proxies from Leaf Fossils Reinterpreted in Light of Evolutionary History
title_full Paleotemperature Proxies from Leaf Fossils Reinterpreted in Light of Evolutionary History
title_fullStr Paleotemperature Proxies from Leaf Fossils Reinterpreted in Light of Evolutionary History
title_full_unstemmed Paleotemperature Proxies from Leaf Fossils Reinterpreted in Light of Evolutionary History
title_short Paleotemperature Proxies from Leaf Fossils Reinterpreted in Light of Evolutionary History
title_sort paleotemperature proxies from leaf fossils reinterpreted in light of evolutionary history
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3008682/
https://www.ncbi.nlm.nih.gov/pubmed/21203554
http://dx.doi.org/10.1371/journal.pone.0015161
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