Despite myriad challenges, clinicians see room for progress.
Image credit: Shutterstock/David Tadevosian.
Edited by Nils Chr. Stenseth, University of Oslo, Oslo, Norway, and approved November 4, 2020 (received for review June 3, 2020)
Significance
There is currently great concern about the ability of organisms to adapt to warmer environments. During heat waves, upper thermal tolerance is often critical for survival, but it is largely unknown how rapidly tolerance can evolve, especially in vertebrates. We artificially selected on upper thermal tolerance in a tropical fish to see whether and how quickly thermal tolerance evolves, and how warm acclimation prior to a thermal challenge alters this evolutionary process. Upper thermal tolerance evolved but at a slow rate toward higher temperature. Furthermore, acclimation capacity decreased in the lines selected for higher thermal tolerance. These results suggest that tropical fishes will struggle to adapt in pace with the current climate warming.
Abstract
Climate change is increasing global temperatures and intensifying the frequency and severity of extreme heat waves. How organisms will cope with these changes depends on their inherent thermal tolerance, acclimation capacity, and ability for evolutionary adaptation. Yet, the potential for adaptation of upper thermal tolerance in vertebrates is largely unknown. We artificially selected offspring from wild-caught zebrafish (Danio rerio) to increase (Up-selected) or decrease (Down-selected) upper thermal tolerance over six generations. Selection to increase upper thermal tolerance was also performed on warm-acclimated fish to test whether plasticity in the form of inducible warm tolerance also evolved. Upper thermal tolerance responded to selection in the predicted directions. However, compared to the control lines, the response was stronger in the Down-selected than in the Up-selected lines in which evolution toward higher upper thermal tolerance was slow (0.04 ± 0.008 °C per generation). Furthermore, the scope for plasticity resulting from warm acclimation decreased in the Up-selected lines. These results suggest the existence of a hard limit in upper thermal tolerance. Considering the rate at which global temperatures are increasing, the observed rates of adaptation and the possible hard limit in upper thermal tolerance suggest a low potential for evolutionary rescue in tropical fish living at the edge of their thermal limits.
Footnotes
- ↵1To whom correspondence may be addressed. Email: rachael.morgan{at}glasgow.ac.uk.
Author contributions: R.M., M.H.F., H.J., C.P., and F.J. designed research; R.M., M.H.F., and F.J. performed research; R.M. analyzed data; R.M., M.H.F., H.J., C.P., and F.J. wrote the paper; and F.J. conceived the experiment.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2011419117/-/DCSupplemental.
Data Availability.
All data and code are freely available on Figshare at: https://figshare.com/articles/dataset/Dataset_and_R_script_for_Low_potential_for_evolutionary_rescue_from_climate_change_in_a_tropical_fish_/12847541/1 (64).
Published under the PNAS license.
References
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Low potential for evolutionary rescue from climate change in a tropical fish
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- Biological Sciences
- Evolution
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