LAUSR

Extant deep-sea fauna, including hydrothermal vent endemics such as bresiliid shrimp, are descended from shallow-water ancestors. Previous studies have demonstrated the capacity of shallow-water shrimp to acclimate to hydrostatic pressure representative of the vent environment. It has been proposed that this hyperbaric acclimation depends in part on shifts in phospholipid fatty acid composition to maintain biomembrane function. These shifts are also predicted to reduce critical temperature tolerance, potentially limiting the possibility of direct colonisation of the hydrothermal vent environment. Here, we present evidence that acclimation to high hydrostatic pressure (10 MPa ≈ 1000 m water depth) decreases acute temperature tolerance from 30.2 °C to 27.1 °C in the shallow-water shrimp Palaemon varians acclimated to 10 °C. Statistically significant shifts in phospholipid fatty acid composition occurred during exposure to high hydrostatic pressure, suggesting that homeoviscous modifications support shifts in environmental tolerances during hyperbaric acclimation. Despite the reduction in temperature tolerance, P. varians retains sufficient thermal scope to tolerate the thermal regime in the hydrothermal vent environment, allowing for the possibility of direct deep-sea hydrothermal vent colonisation by shallow-water shrimp.