Sydney rock oysters on the half shell. Photo from Time Out Sydney www.au.timeout.com
Most species experience many environmental stressors simultaneously which means the direction and magnitude of evolutionary responses will depend on trade-offs between traits whose relationship may prevent them from being simultaneously optimized. Multiple sources of stress may act in opposing ways, for example an increase in salinity tolerance may come at the expense of thermal tolerance, or selection for a particular trait may results in other beneficial changes (adaptive or non-adaptive) in other traits.
Parker et al. (2011) found that Sydney rock oyster larvae selectively bred for fast growth and disease resistance (desirable traits for an economically important, aquaculture species) were more resilient against ocean acidification (OA, i.e. high pCO2 / low pH) than wild type oysters.
[T]he negative impact of exposure to elevated pCO2 on larval shell growth, development and overall survival was significantly lower in S. glomerata bred for disease resistance and fast growth when compared to non-selected ‘wild type’ oysters. Most significantly, it was demonstrated that exposing adults from the S. glomerata selective breeding lines to elevated pCO2 during reproductive conditioning further increased the CO2 tolerance of their larvae.
In a recent Molecular Ecology paper, Thompson et al. used proteomics to test for molecular differences between adult wild type and selectively bred Sydney rock oysters exposed to experimental high pCO2 conditions. They found that the proteomes of the adult oysters changed substantially under OA conditions and that responses varied between the selectively bred and wild type populations. Under high pCO2, the wild type population had an increase in expression of proteins involved in an inducible stress response. However, the selectively bred oysters downregulated these genes and performed poorly under OA.
We argue that this reflects a tradeoff, whereby an adaptive capacity for enhanced mitochondrial energy production in the selectively bred population may help to protect larvae from the effects of elevated CO2, whilst being deleterious to adult oysters.
References:
Parker, L. M., Ross, P. M., Raftos, D., Thompson, E., & O’Connor, W. A. (2011). The proteomic response of larvae of the Sydney rock oyster, Saccostrea glomerata to elevated pCO2. Australian Zoologist, 35(4), 1011-1023. DOI: 10.7882/AZ.2011.056
Thompson, E. L., O’Connor, W., Parker, L., Ross, P., & Raftos, D. A. (2015). Differential proteomic responses of selectively bred and wild Sydney rock oyster populations exposed to elevated CO2. Molecular Ecology. DOI: 10.1111/mec.13111