Parental phenotype and exposure to ocean acidification conditions affect the molecular response of gills in the offspring of a coral reef fish

Abstract

Aim: Ocean acidification can have wide-ranging impacts on marine ecosystems. While short-term studies have reported negative effects of future predicted CO2 levels on a variety of marine organisms, some populations might have the potential to acclimate and/or adapt to elevated CO2 levels across generations. Understanding the capacity of marine organisms to adapt to future CO2 levels will enable us to better predict the biological impacts of ocean acidification. This study therefore focuses on the effects of 1) variation in parental tolerance and 2) parental exposure to elevated CO2, on the molecular responses in the gills of the offspring to elevated CO2 in a coral reef fish. Methods: Adult Acanthochromis polyacanthus were collected from the Great Barrier Reef and classified as either having sensitive or tolerant behavioural phenotype based on their response to chemical alarm cues after elevated CO2 exposure. Breeding pairs of each phenotype were kept in control or elevated CO2 conditions with the resulting offspring reared either in control and elevated CO2 conditions. RNA was extracted from the gills of the offspring, sequenced, and analyzed. Results: Cross-generational exposure to elevated CO2 had a significant impact on gene expression patterns of the offspring. Offspring from parents exposed to elevated CO2 exhibited approximately half the differentially expressed genes compared with offspring in the within-generation elevated CO2 treatment. The parental phenotype also influenced gene expression, with 732 and 183 genes differentially expressed in the control and within-generation CO2 treatment respectively, when comparing directly between offspring of the two parental phenotypes. Main conclusion: Fish whose parents were exposed to elevated CO2 had an enrichment of genes involved in ion regulation and homeostasis related functions and decreased expression of stress response genes compared to the within-generation treatment.