Effects of projected end-of-century temperature on the muscle development of neonate epaulette sharks, Hemiscyllium ocellatum

Epaulette sharks ( Hemiscyllium ocellatum ) inhabit shallow tropical habitats with elevated and fluctuating temperatures. Yet, according to global climate change projections, water temperatures in these habitats will rise beyond current cyclical variability, warranting further studies incorporating chronically elevated temperature exposure in this species. This study examined the differences in skeletal muscle morphological and metabolic properties in neonate epaulette sharks exposed to their current-day ambient (27 °C) or projected end-of-century (31 °C) habitat temperatures throughout embryonic and neonatal development. Metrics of skeletal muscle, such as muscle fiber size and density, nuclear density, and satellite cell density, were used to assess the relative contribution of hypertrophic and hyperplastic growth processes. Capillary density was measured as a proxy for peripheral oxygen supply to muscle tissue. At 31 °C, sharks hatched earlier, but were similar in body size 60 days post-hatch. Muscle fiber size, nuclear density, and capillary density were similar between temperature regimes. However, fiber density was lower, satellite cell density was higher, and fibers associated with satellite cells were smaller in sharks reared at 31 °C. These results suggest that elevated temperature may impair or slow satellite cell fusion to existing fibers and new fiber formation. To assess potential metabolic and developmental consequences of elevated temperatures, oxidative damage (2,4-DNPH, 8-OHdG, 4-HNE), protein degradation (Ubiquitin, LC3B, Hsp70), and muscle differentiation (Myf5, Myogenin) markers were measured. Protein carbonylation was higher at elevated temperatures, suggesting that warmer incubation temperatures at early life stages may result in oxidative damage accrual. However, protein degradation and muscle differentiation markers did not differ. These results suggest that projected end-of-century temperatures may alter muscle growth and metabolism in tropical shark species with potential consequences to shark growth and fitness.