Thyroid-Mediated Metabolic Differences Underlie Ecological Specialization of Extremophile Salmonids in the Arctic Lake El’gygytgyn

El’gygytgyn, the only “ancient lake” in Arctic (3.6 MY), is a deep (176 m) and extremely cold (always ? 4°C) waterbody inhabited by unique salmonids, which colonized ecosystem stepwise during global fluctuations of Quaternary climate. The descendant first-wave-invaders (long-finned charr) dwells waters feeds on amphipods. second-wave-invaders (smallmouth consume copepods mid-waters. Recent third-wave-invaders (Boganida are spread throughout feed insects when they young shifting to piscivory at an older age. Here, we present data charrs’ thyroid status metabolic characteristics, confirming their ecological specialization. long-finned charr exhibits low content, substitution carbohydrates for lipids cellular respiration, increased hemoglobin level high antioxidant blood capacity. These traits likely be legacy anaerobic survival under perennial ice cover several glaciations. Moderate reduced rate smallmouth charr, along with inactive lifestyle, could regarded as specialization saving energy food supply water column. piscivorous Boganida sub-divided into shallow-water deep-water groups. former demonstrates significantly elevated metabolism. latter characterized level, rate, lipid accumulation. Thus, endemic El’gygytgyn charrs represent wide spectrum contrast physiological adaptation patterns essential survive sympatry conditions.