Hypoxia tolerance, but not low pH tolerance, is associated with a latitudinal cline across populations of Tigriopus californicus

Abstract

Intertidal organisms must tolerate daily fluctuations in environmental parameters, and repeated exposure to co-occurring conditions 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 correlates with low pH tolerance by separately testing the hypoxia and low pH stress tolerance separately of 6 genetically differentiated populations of T. californicus. We independently checked for similarities in tolerance for each of the two stressors by latitude, sex, size, and time since collection as predictors. We found that although hypoxia tolerance correlated with latitude, low pH 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. Although climate change alters several environmental variables simultaneously, organisms’ abilities to tolerate these changes may not be similarly coupled.

Mitonuclear effects on sex ratio persist across generations in interpopulation hybrids

“…MtDNA content has been proposed as a biomarker for physiological robustness 66,67,68 as it is positively associated with metabolic efficiency and stress tolerance. Our finding of higher mtDNA content in females is therefore consistent with prior studies in this species showing that females have higher tolerance to a range of stressors including high temperature 46,47,48 , high and low salinity 69,48 , hypoxia 50 , copper 48 , bisphenol A 48 , and paraquat 49 .…”

“…No reuse allowed without permission. consistent with prior studies in this species showing that females have higher tolerance to a range of stressors including high temperature 46,47,48 , high and low salinity 69,48 , hypoxia 50 , copper 48 , bisphenol A 48 , and paraquat 49 .…”

“…T. californicus does not have sex chromosomes (instead, sex determination is polygenic 42,43,44,45 ), which means that sexspecific mitochondrial effects are not confounded with sex chromosome effects. Despite the absence of sex chromosomes in this species, males and females show substantial differences in stress tolerance 46,47,48,49,50 and gene expression 51,52 .…”