Physiological acclimatization in high-latitude zooplankton

How individual organisms adapt to non-optimal conditions through
physiological acclimatization is central to predicting the consequences of
unusual abiotic and biotic conditions such as those produced by marine
heat waves. The Northeast Pacific, including the Gulf of Alaska
experienced an extreme warming event (2014-2016, “The Blob”) that affected
all trophic levels leading to large-scale changes in the community. The
marine copepod Neocalanus flemingeri is one key member
of the subarctic Pacific pelagic ecosystem. During the spring
phytoplankton bloom this copepod builds substantial lipid stores as it
prepares for its non-feeding adult phase. A three-year comparison of gene
expression profiles of copepods collected in Prince William Sound in the
Gulf of Alaska between 2015 and 2017 included two high-temperature years
(2015 and 2016) and one year with very low phytoplankton abundances
(2016). The largest differences in gene expression were between high and
low chlorophyll years, and not between warm and cool years. The observed
gene expression patterns are indicative of physiological acclimatization.
The predominant signal in 2016 was the down-regulation of genes involved
in glycolysis and its incoming pathways, consistent with the modulation of
metabolic rates in response to prolonged low food conditions. Despite the
down-regulation of genes involved in metabolism, there was no evidence of
suppression of protein synthesis based on gene expression or behavioral
activity. Genes involved in muscle function were up-regulated, and the
copepods were actively swimming and responsive to stimuli at collection.
However, genes involved in fatty acid metabolism were down-regulated in
2016, suggesting reduced lipid accumulation.