Evidence of fast adaption to ocean acidification in a pelagic copepod

Chair: Philip Munday

Peter Thor (1)*, Pierre De Wit (2), Sam Dupont (3)

1 Norwegian Polar Institute, Framcentre, Tromsø, NO-9296, Norway
2 University of Gothenburg, Dept. of Marine Sciences – Tjärnö, Strömstad, SE-452 96, Sweden
3 University of Gothenburg, Dept. of Marine Sciences – Kristineberg, Fiskebäckskil, SE-451 78, Sweden

Background
The rate of ocean acidification (OA) relative to generation time of most species leaves considerable room for genetic adaptation of populations through natural selection. Much focus is therefore directed at investigations of adaptation to future OA.

Methods
The pelagic copepod Pseudocalanus acuspes were reared for two generations at three different CO2 partial pressures (400, 900 and 1550 µatm) followed by reciprocal transplant tests (RTT) to reveal transgenerational effects/adaptation.

Findings
Second generation adults showed a 29% decrease in fecundity at 900 µatm CO2 compared to 400 µatm CO2. This was accompanied by a 10% increase in metabolic rate, which indicates metabolic stress. RTTs demonstrated that these effects were a result of phenotypic plasticity. Furthermore, RTTs showed that at 1550 µatm fecundity would have decreased by as much as 67% compared to at 400 µatm as a result of such plasticity. However, transgenerational buffering partly reduced effects and the loss of fecundity remained at a level comparable to at 900 µatm. Moreover, respiration rates at 1550 µatm were lower than at 900 µatm.

Transcriptomic analysis revealed concurrent significant down-regulation of 353 genes involved in RNA transcription. In addition we found 1513 single nucleotide polymorphisms indicating consistent changes in nucleotide frequency. Within this dataset, functions involving RNA transcription and ribosomal function, as well as ion transport and oxidative phosphorylation were highly overrepresented.

Conclusions
Severe OA effects on copepod fecundity may be alleviated by selection on the level of RNA transcription and ribosomal function, possibly modulated by changes in helicase expression. This may also relieve the copepods from metabolic stress.