Age-dependent expression of stress and antimicrobial genes in the hemocytes and siphon tissue of the Antarctic bivalve, Laternula elliptica, exposed to injury and starvation.

Increasing temperatures and glacier melting at the Western Antarctic Peninsula (WAP) are causing rapid changes in shallow coastal and shelf systems. Climate change-related rising water temperatures, enhanced ice scouring, as well as coastal sediment runoff, in combination with changing feeding conditions and microbial community composition, will affect all elements of the nearshore benthic ecosystem, a major component of which is the Antarctic soft-shelled clam Laternula elliptica. A 454-based RNA sequencing was carried out on tissues and hemocytes of L. elliptica, resulting in 42,525 contigs, of which 48 % was assigned putative functions. Changes in the expression of putative stress response genes were then investigated in hemocytes and siphon tissue of young and old animals subjected to starvation and injury experiments in order to investigate their response to sedimentation (food dilution and starvation) and iceberg scouring (injury). Analysis of antioxidant defense (Le-SOD and Le-catalase), wound repair (Le-TIMP and Le-chitinase), and stress and immune response (Le-HSP70, Le-actin, and Le-theromacin) genes revealed that most transcripts were more clearly affected by injury rather than starvation. The upregulation of these genes was particularly high in the hemocytes of young, fed individuals after acute injury. Only minor changes in expression were detected in young animals under the selected starvation conditions and in older individuals. The stress response of L. elliptica thus depends on the nature of the environmental cue and on age. This has consequences for future population predictions as the environmental changes at the WAP will differentially impact L. elliptica age classes and is bound to alter population structure.