Love thy neighbor: Social buffering following exposure to an acute thermal stressor in a gregarious fish, the lake sturgeon (Acipenser fulvescens).

Social buffering is a phenomenon where the presence of conspecifics reduces an animal's stress response. Well known in mammals, social buffering was recently described in fishes exhibiting pronounced social hierarchies. Lake sturgeon (Acipenser fulvescens) are a gregarious rather than hierarchical fish. Therefore, we tested their capacity for social buffering following exposure to an acute thermal stress. Isolated or grouped (three or six similarly sized conspecifics) age-0 lake sturgeon were exposed to a critical thermal maximum (CT) test. We measured the endocrine and cellular response to acute thermal shock by assessing whole body cortisol concentration and mRNA expression of steroidogenic acute regulatory protein (StAR) and heat shock proteins (hsp90a, hsp90b, and hsp70) during recovery from the CT test. Isolation or grouping had no effect on CT. Whole body cortisol concentrations in isolated fish were approximately three-fold higher than in grouped fish 1 h post-CT and two-fold higher than grouped fish 20 h post-CT. Similarly, 1 h post-CT, mRNA expression of StAR, hsp90a, hsp90b and hsp70 were three to four-fold higher in isolated fish compared to groups of three and six fish. At 20 h post-CT, expression of StAR was approximately two-fold higher in isolated fish, but expression of hsp90a, hsp90b, and hsp70 was not significantly different between isolated and grouped fish. While conspecific presence had no effect on CT, the significant reduction of endocrine and cellular stress markers post-CT in grouped fish strongly suggests that lake sturgeon may use social buffering to combat potential deleterious effects of exposure to heat stress.