Transcriptomic Response of the Atlantic Surfclam (Spisula solidissima) to Acute Heat Stress.

There is clear evidence that the oceans are warming due to anthropogenic climate change, and the northeastern coast of USA contains some of the fastest warming areas. This warming is projected to continue with serious biological and social ramifications for fisheries and aquaculture. One species particularly vulnerable to warming is the Atlantic surfclam (Spisula solidissima). The surfclam is a critically important species, linking marine food webs and supporting a productive, lucrative, and sustainable fishery. The surfclam is also emerging as an attractive candidate for aquaculture diversification, but the warming of shallow coastal farms threatens the expansion of surfclam aquaculture. Little is known about the adaptive potential of surfclams to cope with ocean warming. In this study, the surfclam transcriptome under heat stress was examined. Two groups of surfclams were subjected to heat stress to assess how artificial selection may alter gene expression. One group of clams had been selected for greater heat tolerance (HS) and the other was composed of random control clams (RC). After a 6-h exposure to 16 or 29 °C, gill transcriptome expression profiles of the four temperature/group combinations were determined by RNA sequencing and compared. When surfclams experienced heat stress, they exhibited upregulation of heat shock proteins (HSPs), inhibitors of apoptosis (IAPs), and other stress-response related genes. RC clams differentially expressed 1.7 times more genes than HS clams, yet HS clams had a stronger response of key stress response genes, including HSPs, IAPs, and genes involved with mitigating oxidative stress. The findings imply that the HS clams have a more effective response to heat stress after undergoing the initial selection event due to genetic differences created by the selection, epigenetic memory of the first heat shock, or both. This work provides insights into how surfclams adapt to heat stress and should inform future breeding programs that attempt to breed surfclam for greater heat tolerance, and ultimately bring greater resiliency to shellfish farms.

Effects of Embryonic Exposure to Salinity Stress or Hypoxia on Post-metamorphic Growth and Survival of the Polychaete Capitella teleta.

Although a good number of studies have investigated the impact of larval experience on aspects of post-metamorphic performance, only a few have considered the potential impact of stresses experienced by brooded embryos. In this study we separately investigated the impact of salinity stress (as low as 10) and hypoxia (1 ml O2 l-1) experienced by brooded embryos of the deposit-feeding polychaete Capitella teleta on hatching success, metamorphosis, post-metamorphic survival, and post-metamorphic growth. Salinity reduction from 30 to 10 or 15 reduced relative hatching success, presumably by reducing embryonic survival, but generally had no negative latent effects on juvenile survival or growth. Prolonged exposure to hypoxic conditions had no negative effects, as seen on measurements recorded, other than abandonment of brood tubes by some females. There were no negative effects on days to emergence from brood tubes, numbers of larvae emerging from brood tubes, juvenile survival, or juvenile growth. Future studies should consider the potential role of maternal behavior in protecting embryos from at least short-term exposures to hypoxia, and the capacity for anaerobic metabolism in both embryos and adults of this species.