DOI: 10.5061/dryad.qj947s3
title: Data from: An extinction event in planktonic Foraminifera preceded by stabilizing selection

description: Unless they adapt, populations facing persistent stress are threatened by
 extinction. Theoretically, populations facing stress can react by either
 disruption (increasing trait variation and potentially generating new
 traits) or stabilization (decreasing trait variation). In the short term,
 stabilization is more economical, because it quickly transfers a large
 part of the population closer to a new ecological optimum. However,
 canalization is deleterious in the face of persistently increasing stress,
 because it reduces variability and thus decreases the ability to react to
 further changes. Understanding how natural populations react to
 intensifying stress reaching terminal levels is key to assessing their
 resilience to environmental change such as that caused by global warming.
 Because extinctions are hard to predict, observational data on the
 adaptation of populations facing extinction are rare. Here, we make use of
 the glacial salinity rise in the Red Sea as a natural experiment allowing
 us to analyse the reaction of planktonic Foraminifera to stress escalation
 in the geological past. We analyse morphological trait state and variation
 in two species across a salinity rise leading to their local extinction.
 One species reacted by stabilization in shape and size, detectable several
 thousand years prior to extinction. The second species reacted by trait
 divergence, but each of the two divergent populations remained stable or
 reacted by further stabilization. These observations indicate that the
 default reaction of the studied Foraminifera is canalization, and that
 stress escalation did not lead to the emergence of adapted forms. An
 inherent inability to breach the global adaptive threshold would explain
 why communities of Foraminifera and other marine protists reacted to
 Quaternary climate change by tracking their zonally shifting environments.
 It also means that populations of marine plankton species adapted to
 response by migration will be at risk of extinction when exposed to stress
 outside of the adaptive range.
description: Age model
 Age model used
 for the analyses. Tie points provided by Katherine Grant (Australian
 National University) based on Grant et al. (2014) Nature Communications 5:
 Article 5076, doi:10.1038/ncomms6076 Age_Model.txt
 
 Oceanography
 This file
 contains the oceanographic data from the investigated time interval in the
 Red Sea. Modified from Rohling et al. (2009), Nature Geoscience 2:
 500-504, doi:10.1038/ngeo557 Oceanography.txt Abundances Abundance data for <em>Orbulina universa</em> and <em>Trilobatus sacculifer</em> in the analysed sediment samples. Abundances.txt <em>O. universa</em> morphology data Morphological data of <em>Orbulina universa</em> from the analysed sediment samples. OUniversa_Morphology.txt <em>T. sacculifer</em> metadata Metadata for <em>Trilobatus sacculifer</em> specimens in the analysed samples. TSacculifer_Metadata.txt <em>T. sacculifer</em> morphology data Morphological landmark data of <em>Trilobatus sacculifer</em> from the analysed sediment samples in .tps-format. TSacculifer_Morphology.zip README Plain .txt file. This file contains detailed information about the other supplementary files. README.txt
description: The data were collected from sediment taken with a piston corer
 in the Red Sea. Morphometric data were extracted from high resolution
 light microscopy images.