Genomic, transcriptomic and epigenomic signatures of ageing and cold adaptation in the Antarctic clam Laternula elliptica

Genomic data are lacking for most Antarctic marine invertebrates, predicating our ability to understand physiological adaptation and specific life-history traits, such as longevity. The environmental stress response of the Antarctic infaunal clam Laternula elliptica is much diminished in older adult animals compared with younger juvenile individuals. However, the mechanism underlying this reduced capacity is unknown. In this study, we describe and analyse the genome of L. elliptica and use it as a tool to understand transcriptomic responses to shell damage across different age cohorts. Gene expression data were combined with reduced representation enzymic methyl sequencing to identify if methylation was acting as an epigenetic mechanism driving age-dependent transcriptional profiles. Our transcriptomic results demonstrated a clear bipartite molecular response in L. elliptica, associated with a rapid growth phase in juveniles and a stabilization phase in reproductively mature adults. Genes active in the response to damage repair in juvenile animals are silent in adults but can be reactivated after several months following damage stimulus; however, these genes were not methylated. Hence, the trigger for this critical and imprinted change in physiological state is, as yet, unknown. While epigenetics is likely involved in this process, the mechanism is unlikely to be methylation.