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Heat shock response (HSR), in terms of transcription regulation of two heat shock proteins genes hsp70 and hsp90), was analysed in a widespread tropical copepod Pseudodiaptomus annandalei. The mRNA transcripts of both genes were quantified after copepods at a salinity of 20 underwent an acclimation process involving an initial acclimation temperature of 29 °C, followed by gradual thermal ramping to the target exposure temperature range of 24-36 °C. The respective cellular HSR and organismal metabolism, measured by respiratory activity at exposure temperatures, were compared. The fold change in mRNA expression for both hsp70 and hsp90 (8-9 fold) peaks at 32 °C, which is very close to 32.4 °C, the upper thermal optimum for respiration in the species. Unexpectedly, the modelled HSR curves peak at only 3 °C (hsp90) and 3.5 °C (hsp70) above the mean water temperature (29.32 °C) of the copepod in the field. We propose that copepods in tropical waters adopt a preparative HSR strategy, early at the upper limit of its thermal optimum, due to the narrow thermal range of its habitat thus precluding substantial energy demand at higher temperatures. However, the model suggests that the species could survive to at least 36 °C with short acclimation time. Nevertheless, the significant overlap between its thermal range of hsp synthesis and the narrow temperature range of its habitat also suggests that any unprecedented rise in sea temperature would have a detrimental effect on the species., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Thermal specialization could explain the dominance of some marine crustaceans in thermostable conditions but fluctuations below their natural thermal environment should substantially disrupt physiological rates. This study shows how developmental cold acclimation below the thermal optimum significantly helps mitigate the decay of the weight-specific respiration rate (Rsp) in a widespread tropical copepod (Pseudodiaptomus annandalei Sewell, 1919) as compared to cold acclimation during the adult stage only. The measurement of routine respiration is of valuable physiological interest, as experimental results on P. annandalei identified the lower thermal limit for optimal respiration and confirmed this species as a thermal specialist given its narrow thermal window that closely overlapped the natural thermal regime in the area. The implications of a higher than expected Rsp in a colder environment during the entire life cycle as compared to traditional short-term experiments are discussed in view of the controversial theory of metabolic cold adaptation. [ABSTRACT FROM AUTHOR]

Abstract: Carbon dioxide production rates of mixed epipelagic copepods were measured during the so-called late winter bloom in the vicinity of the Canary Islands. Respiration rates were measured using a simple and sensitive infra-red gas analyser coupled to a manifold containing an equilibrator module to transfer seawater CO2 to the gas phase. The system allowed the determination of the carbon dioxide content of one sample in 20 to 40min. Respiration rates obtained were similar to previous oxygen consumption rates in subtropical waters. A relative wide range of carbon dioxide production rates was observed due to the metabolic condition of the organisms. Direct measurement of respiration rates after the capture showed high values (11-fold) compared to standard rates at starving conditions after only 4–6h of incubation in filtered seawater. The results showed that short-term (0.5h) CO2 production rates by copepods can be measured in relatively large incubation volumes (600ml) minimizing crowding and bottle effects. A standardized method is proposed in order to obtain comparable results of metabolic rates in marine mesozooplankton. [Copyright &y& Elsevier]