Damaging effects and altered gene expression from temperature stress in early life-stages of Atlantic tomcod from the Hudson River

The Hudson River (HR), New York, has been rapidly warming, with water temperatures increasing 1 °C between 1946 and 2006 and projected to rise at an even faster rate in the future. Atlantic tomcod Microgadus tomcod is a cold water, estuarine, Gadidae species whose current southern distribution along the Atlantic coast of North America is truncated by warming waters. Currently, the HR supports their southernmost spawning population whose abundance is in severe decline. We used controlled laboratory experiments to investigate the effects of projected warming HR wintertime water temperatures on a number of fitness measures in tomcod embryos and larvae. We found that higher temperatures increased hatch rate, growth rate, heart rates, mortality of larvae, and differentially expressed genes (DEGs). The number of DEGs identified by RNA-Seq analysis (≥ 2-fold change, FDR <0.1) increased when comparing the control 2.7 °C temperature group to the higher temperature exposure groups. For example, the number of DEGs was 349, 565, and 1286 when comparing the control exposure group to the groups exposed to 3.5 °C, 6.2 °C, and 8.3 °C water temperatures, respectively. DEGs genes were linked to stress response, cardiac health, and protein homeostasis. These findings indicate that Atlantic tomcod respond to temperature stress by downregulating energy-intensive processes like protein homeostasis, posing potential long-term health risks to its HR population.