ALBERT

Description: Differences in the sensitivity of marine species to ocean acidification will influence the structure of marine communities in the future. Reproduction is critical for individual and population success, yet is energetically expensive and could be adversely affected by rising CO2 levels in the ocean. We investigated the effects of projected future CO2 levels on reproductive output of two species of coral reef damselfish, Amphiprion percula and Acanthochromis polyacanthus. Adult breeding pairs were maintained at current-day control (446 µatm), moderate (652 µatm) or high CO2 (912 µatm) for a 9-month period that included the summer breeding season. The elevated CO2 treatments were consistent with CO2 levels projected by 2100 under moderate (RCP6) and high (RCP8) emission scenarios. Reproductive output increased in A. percula, with 45-75 % more egg clutches produced and a 47-56 % increase in the number of eggs per clutch in the two elevated CO2 treatments. In contrast, reproductive output decreased at high CO2 in Ac. polyacanthus, with approximately one-third as many clutches produced compared with controls. Egg survival was not affected by CO2 for A. percula, but was greater in elevated CO2 for Ac. polyacanthus. Hatching success was also greater for Ac. polyacanthus at elevated CO2, but there was no effect of CO2 treatments on offspring size. Despite the variation in reproductive output, body condition of adults did not differ between control and CO2 treatments in either species. Our results demonstrate different effects of high CO2 on fish reproduction, even among species within the same family. A greater understanding of the variation in effects of ocean acidification on reproductive performance is required to predict the consequences for future populations of marine organisms.

Description: Knowledge of adaptive potential is crucial to predicting the impacts of ocean acidification (OA) on marine organisms. In the spiny damselfish, Acanthochromis polyacanthus, individual variation in behavioural tolerance to elevated pCO2 has been observed and is associated with offspring gene expression patterns in the brain. However, the maternal and paternal contributions of this variation are unknown. To investigate parental influence of behavioural pCO2 tolerance, we crossed pCO2-tolerant fathers with pCO2-sensitive mothers and vice versa, reared their offspring at control and elevated pCO2 levels, and compared the juveniles' brain transcriptional programme. We identified a large influence of parental phenotype on expression patterns of offspring, irrespective of environmental conditions. Circadian rhythm genes, associated with a tolerant parental phenotype, were uniquely expressed in tolerant mother offspring, while tolerant fathers had a greater role in expression of genes associated with histone binding. Expression changes in genes associated with neural plasticity were identified in both offspring types: the maternal line had a greater effect on genes related to neuron growth while paternal influence impacted the expression of synaptic development genes. Our results confirm cellular mechanisms involved in responses to varying lengths of OA exposure, while highlighting the parental phenotype's influence on offspring molecular phenotype.

Description: The impacts of ocean acidification will depend on the ability of marine organisms to tolerate, acclimate and eventually adapt to changes in ocean chemistry. Here, we use a unique transgenerational experiment to determine the molecular response of a coral reef fish to short-term, developmental and transgenerational exposure to elevated CO2, and to test how these responses are influenced by variations in tolerance to elevated CO2 exhibited by the parents. Within-generation responses in gene expression to end-of-century predicted CO2 levels indicate that a self-amplifying cycle in GABAergic neurotransmission is triggered, explaining previously reported neurological and behavioural impairments. Furthermore, epigenetic regulator genes exhibited a within-generation specific response, but with some divergence due to parental phenotype. Importantly, we find that altered gene expression for the majority of within-generation responses returns to baseline levels following parental exposure to elevated CO2 conditions. Our results show that both parental variation in tolerance and cross-generation exposure to elevated CO2 are crucial factors in determining the response of reef fish to changing ocean chemistry.