Diurnal and seasonal hsp70 gene expression in a cryptic reef fish, the bluebanded goby Lythrypnus dalli (Gilbert 1890)

Physiological responses of marine organisms are influenced by environmental variations, particularly in dynamic habitats. These variations could be at a diel or seasonal scale, and requires acclimation responses that, at a molecular level, are facilitated by gene expression regulation. Circadian rhythms allow organisms to adjust to recurring environmental changes and to synchronize physiological processes. Increased Hsp70 gene expression allows organisms to protect themselves against heat and other stressors, conferring them a periodically changing thermotolerance. This study aimed at analyzing whether the variability of exogenous factors (temperature, dissolved oxygen, salinity) in diurnal or seasonal scales affects hsp70 expression in cryptic reef fishes in their natural environment. The study model was Lythrypnus dalli, an endemic cryptic reef fish inhabiting shallow waters throughout the Gulf of California. Physical parameters varied seasonally; temperature increased 6 degrees C during the warm season, salinity and dissolved oxygen remained with minor variation. Minimal changes in temperature (+/- 1 degrees C) occurred diurnally. Expression levels of hsp70 increased significantly during the warm season (p < 0.05), perhaps related to seasonal thermal changes. No difference in hsp70 was observed during the diurnal cycle (p > 0.05). L. dalli has apparently developed phenotypic plasticity to face environmental variability at diurnal and seasonal scales.