Standing genetic variation fuels rapid adaptation to ocean acidification

M C Bitter,J.-P Gattuso,C A Pfister,L Kapsenberg

doi:10.1038/s41467-019-13767-1

M C Bitter, J.-P Gattuso + Show 2 more

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https://doi.org/10.1038/s41467-019-13767-1

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Abstract

Global climate change has intensified the need to assess the capacity for natural populations to adapt to abrupt shifts in the environment. Reductions in seawater pH constitute a conspicuous global change stressor that is affecting marine ecosystems globally. Here, we quantify the phenotypic and genetic modifications associated with rapid adaptation to reduced seawater pH in the Mediterranean mussel, Mytilus galloprovincialis. We reared a genetically diverse larval population in two pH treatments (pHT 8.1 and 7.4) and tracked changes in the shell-size distribution and genetic variation through settlement. Additionally, we identified differences in the signatures of selection on shell growth in each pH environment. Both phenotypic and genetic data show that standing variation can facilitate adaptation to declines in seawater pH. This work provides insight into the processes underpinning rapid evolution, and demonstrates the importance of maintaining variation within natural populations to bolster species’ adaptive capacity as global change progresses.

Highlights

Global climate change has intensified the need to assess the capacity for natural populations to adapt to abrupt shifts in the environment
Larvae were reared in ambient and low-pH and (i) shell-size distributions were quantified on days 3, 6, 7, 14, and 26; (ii) the frequency of 29,400 single nucleotide polymorphisms (SNPs) across the species’ exome was estimated on days 6, 26, and 43; and (iii) signatures of selection on larval shell size were determined in each treatment
While previous work has shown strong negative effects of low pH on larval development in bivalves[17,18,19,24], the results presented here suggest that standing variation within the species could facilitate rapid adaptation to ocean acidification

Summary

Introduction

Global climate change has intensified the need to assess the capacity for natural populations to adapt to abrupt shifts in the environment. Environmental gradients in marine systems can maintain signatures of balanced polymorphisms between populations at multiple, putatively functional loci, even amidst high levels of gene flow[9,10,11,12] While this variation has enabled the persistence of natural populations inhabiting the contemporary and historic regimes of environmental variability, it is unclear whether it will facilitate the magnitude and rate of adaptation necessary for species persistence under the conditions expected as a result of global climate change[13]. While our low-pH treatment falls below the expected 0.4 pHT unit decline in global mean seawater pH by 210014, marine species occupying unequilibrated coastal regions, such as the lagoon habitat of the study population, may periodically experience pH conditions that fall far below projected means during the century[22]

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