Acute high temperature exposure impairs hypoxia tolerance in an intertidal fish.

Tristan J Mcarley,Neill A Herbert,Anthony J R Hickey,Rui Rosa

doi:10.1371/journal.pone.0231091

Abstract

Acute heat shock has previously been shown to improve subsequent low O2 (hypoxia) tolerance in an intertidal fish species, a process known as cross-tolerance, but it is not known whether this is a widespread phenomenon. This study examined whether a rock pool specialist, the triplefin fish Bellapiscis medius, exhibits heat shock induced cross-tolerance to hypoxia, i.e., longer time to loss of equilibrium (LOE) and lower critical O2 saturation (Scrit) after recovering from an acute heat challenge. Non-heat shock controls had a median time to loss of equilibrium (LOE50) of 54.4 min under severe hypoxia (7% of air saturation) and a Scrit of 15.8% air saturation. Contrary to expectations, however, treatments that received an 8 or 10°C heat shock showed a significantly shorter LOE50 in hypoxia (+8°C = 41.5 min; +10°C = 28.7 min) and no significant change in Scrit (+8°C = 17.0% air saturation; +10°C = 18.3% of air saturation). Thus, there was no evidence of heat shock induced cross-tolerance to hypoxia in B. medius because exposure to acute heat shock impaired hypoxia tolerance.

Highlights

Marine organisms commonly have to contend with fluctuating environmental conditions severe enough to elicit a physiological stress response
In order to build upon the findings of Todgham et al, (2005) [12], the present study examined cross-tolerance in another specialist intertidal fish (Bellapiscis medius, Gunther, 1861) to assess whether heat shock induced cross-tolerance is a common response in rock pool fishes
Post-hoc comparisons showed the median time to loss of equilibrium was significantly shorter in the +8 ̊C heat shock group (LOE50 = 41.5 min) compared to the control group ((LOE50 = 54.4 min), and significantly shorter again in the +10 ̊C heat shock group (LOE50 = 28.7 min) compared to both the control and +8 ̊C heat shock group (Fig 1)

Summary

Introduction

Marine organisms commonly have to contend with fluctuating environmental conditions (e.g. temperature, salinity, and oxygen) severe enough to elicit a physiological stress response. Environmental parameters rarely occur in isolation, so organisms must endure multiple environmental conditions that fluctuate either simultaneously or sequentially [1]. When organisms experience multiple stressors simultaneously or in rapid succession, the combined negative effect is sometimes amplified (synergistic) relative to the additive effects of the individual stressors acting in isolation [1,2,3]. If there is a sufficient period of recovery between exposures, the combined negative effect of the stressors can be equal to the sum of the individual stressor effects (additive) or even reduced (antagonistic) [1,2]. In the case of an antagonistic response, exposure to one stressor can sometimes increase the tolerance of an organism to a second stressor; this phenomenon is known as cross-tolerance [4]

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Conclusion