Natural CO2 seeps reveal adaptive potential to ocean acidification in fish

Volcanic CO2 seeps are natural laboratories that can provide insights into the adaptation of species to ocean acidification. While many species are challenged by reduced-pH levels, some species benefit from the altered environment and thrive. Here, we explore the molecular mechanisms of adaptation to ocean acidification in a population of a temperate fish species that experiences increased population sizes under elevated CO2. Fish from CO2 seeps exhibited an overall increased gene expression in gonad tissue compared with those from ambient CO2 sites. Up-regulated genes at CO2 seeps are possible targets of adaptive selection as they can directly influence the physiological performance of fishes exposed to ocean acidification. Most of the up-regulated genes at seeps were functionally involved in the maintenance of pH homeostasis and increased metabolism, and presented a deviation from neutral evolution expectations in their patterns of DNA polymorphisms, providing evidence for adaptive selection to ocean acidification. The targets of this adaptive selection are likely regulatory sequences responsible for the increased expression of these genes, which would allow a fine-tuned physiological regulation to maintain homeostasis and thrive at CO2 seeps. Our findings reveal that standing genetic variation in DNA sequences regulating the expression of genes in response to a reduced-pH environment could provide for adaptive potential to near-future ocean acidification in fishes. Moreover, with this study we provide a forthright methodology combining transcriptomics and genomics, which can be applied to infer the adaptive potential to different environmental conditions in wild marine populations.

Automated summary

Volcanic CO2 seeps can provide insights into species adaptation to ocean acidification, with some species benefiting from the altered environment. A study on a temperate fish species at CO2 seeps showed increased gene expression in gonad tissue, with up-regulated genes involved in pH homeostasis maintenance and increased metabolism, deviating from neutral evolution expectations and providing evidence for adaptive selection to ocean acidification. Adaptive selection likely targets regulatory sequences responsible for increased gene expression, allowing for fine-tuned physiological regulation to thrive at CO2 seeps. The study suggests that genetic variation in gene regulatory sequences could provide adaptive potential to future ocean acidification in fishes, and the methodology combining transcriptomics and genomics can be applied to infer adaptive potential in wild marine populations.