Bivalve aquaculture is an important activity able to provide healthy food with a low carbon footprint. T his activity is threatened by climate extreme events such as marine heatwaves (MHWs), which are increasing their frequency, duration and intensity every year. In shellfish farming the scope for contrasting the impact of MHWs is limited . Selective breeding for organisms that are more resilient to MHW may be an effective solution against these stressful events and may, in turn, sustain the clam aquaculture sector. Within this framework, genome wide association studies (GWAS) supported by SNP array genotyping is a powerful tool to investigate the genetic basis of such complex (and possibly multigenic) traits.
For this task we initially designed a novel multi-species Axiom SNP array (60K) with ~45K SNPs for the Manila clam (Ruditapes philippinarum) and ~15K SNPs for the carpet shell clam ( R. decussatus ). The array was subsequently used aiming to identify quantitative trait loci (QTLs) significantly linked with the trait resistance to MHWs.
To fulfil our aim, we exposed a population of 1000 Manila clams, obtained from a mass spawning event at the Satmar hatchery, to a simulated MHW that mimicked a natural event which occurred in the Venice lagoon in 2015, with water temperatures fluctuating daily between 31 and 35 ˚ C. Animals were randomly split across 10 aquaria and the MHW was replicated across all the experimental tanks, lasting 15 days. After this period, we stopped the MHW and kept the remaining animals at 25 ˚ C until no more casualties were observed in the population. All samples were genotyped with the Axiom SNP-array. We evaluated the resistance to MHW as both a binary trait (i.e. resistant vs susceptible) and as a continuous trait (i.e. time to death). By identifying genetic markers associated with MHW resistance, this research paves the way for developing more resilient clam populations through genomic driven selective breeding, potentially revolutionizing the aquaculture industry’s ability to adapt to climate change challenges.