Latitudinal cline in hypoxia tolerance does not result in correlated acid tolerance in Tigriopus californicus

Abstract

Intertidal organisms must tolerate a wide range of environmental parameters each day which may result in tolerance to multiple stressors correlating. The intertidal copepod Tigriopus californicus experiences diurnal variation in dissolved oxygen levels and pH as the opposing processes of photosynthesis and cellular respiration lead to coordinated highs during the day and lows at night. While environmental parameters with overlapping spatial gradients frequently result in correlated traits, less attention has been given to exploring temporally correlated stressors. We investigated whether hypoxia tolerance correlated with acid tolerance by testing the hypoxia and low pH stress tolerance of 6 genetically differentiated populations of T. californicus. We checked for similarities in tolerance for the two stressors by latitude, sex, size, and time since collection as predictors. We found that although hypoxia tolerance correlated with latitude, acid tolerance did not, and no predictor was significant for both stressors. We concluded that temporally coordinated exposure to low pH and low oxygen did not result in populations developing equivalent tolerance for both.