Natural CO2 seeps give clues about fish adaptation to ocean acidification

Abstract

Volcanic CO2 seeps at White Island (New Zealand) are natural laboratories that provide insights into the effects of ocean acidification on fishes in nature. The common triplefin, Forsterygion lapillum, is a behaviourally dominant species at these seeps with significantly greater population densities than at sites with ambient CO2 levels (1). These observations together with some other behavioural and physiological traits suggest that common triplefin have successfully adapted to live in a low pH environment (1). However, little is known about the mechanisms that allow life in such an environment. In this study, we contrast the levels of gene expression in gonads from triplefins collected at CO2 seeps (lower pH, N=10) and neighbouring controls (ambient pH, N=10). The body length of the collected individuals was recorded and their RNA was extracted and sequenced. RNA-seq reads were de novo assembled and a good-quality reference transcriptome for common triplefin was built using gene orthology data from genomes of related species (N=13,603 genes). Gene expression quantification revealed that the average gene expression across the whole transcriptome is significantly higher in individuals from CO2 seeps than in neighbouring zones. Differences in average gene expression were significant for males but not for females. Fishes from the CO2 vents showed 66 up-regulated genes related with different functions, especially with transmembrane transport, metal ion binding and oxidation-reduction processes. These observations suggest that higher levels of gene expression in males from CO2 seeps are an adaptive response for maintenance of cellular homeostasis and energy production.