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Biology (Basel)
2024 Mar 29;134:. doi: 10.3390/biology13040224.
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Testing the Resilience, Physiological Plasticity and Mechanisms Underlying Upper Temperature Limits of Antarctic Marine Ectotherms.
Morley SA
,
Bates AE
,
Clark MS
,
Fitzcharles E
,
Smith R
,
Stainthorp RE
,
Peck LS
.
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Antarctic marine ectotherms live in the constant cold and are characterised by limited resilience to elevated temperature. Here we tested three of the central paradigms underlying this resilience. Firstly, we assessed the ability of eight species, from seven classes representing a range of functional groups, to survive, for 100 to 303 days, at temperatures 0 to 4 °C above previously calculated long-term temperature limits. Survivors were then tested for acclimation responses to acute warming and acclimatisation, in the field, was tested in the seastar Odontaster validus collected in different years, seasons and locations within Antarctica. Finally, we tested the importance of oxygen limitation in controlling upper thermal limits. We found that four of 11 species studied were able to survive for more than 245 days (245-303 days) at higher than previously recorded temperatures, between 6 and 10 °C. Only survivors of the anemone Urticinopsis antarctica did not acclimate CTmax and there was no evidence of acclimatisation in O. validus. We found species-specific effects of mild hyperoxia (30% oxygen) on survival duration, which was extended (two species), not changed (four species) or reduced (one species), re-enforcing that oxygen limitation is not universal in dictating thermal survival thresholds. Thermal sensitivity is clearly the product of multiple ecological and physiological capacities, and this diversity of response needs further investigation and interpretation to improve our ability to predict future patterns of biodiversity.
Figure 1. The Kaplan-Meier estimate of median survival duration, in days, after incubation at 6.0 and 8.0 °C. Species ordered from lowest to highest survival. Median ± interquartile range. Hashed lines indicate the duration of experiments for species for which the Kaplan-Meier estimator could not be calculated as most individuals survived until the experiment ended (censored observations), except for O. validus at 8.0 °C when the experiment terminated after 200 days due to a heater failure. Missing interquartile ranges indicate that the Kaplan-Meier could not estimate that value (Table S1). An asterix (*) indicates significantly different survival of that species between incubation temperatures. See Figure S1 for the stability of incubation temperatures and Figure S2 for Kaplan-Meier estimation figures.
Figure 2. Lethal temperature limits in four Antarctic marine invertebrates incubated in the laboratory at 0.0, 6.0 and 8.0 °C. (A) Urticinopsis antarctica, (B) Heterocucumis steineni, (C) Odontaster validus, and (D) Sterechinus neumayeri. U. antarctica was the only species whose CTmax did not acclimate between control (0.0 °C) and elevated temperatures (6 and 8.0 °C). Where more than one data point is shown for a given temperature, more than one experiment was conducted at different times. Urticinopsis antarctica, 0 °C n = 14, 6 °C n = 13, Heterocucumis steineni, n = 19 to 24, Odontaster validus, 0 °C n = 14, 6 °C n = 19 and Sterechinus neumayeri, 0 °C n = 12 and 8, 6 °C n = 21, 8 °C n = 10.
Figure 3. Upper lethal limits of Odontaster validus tested directly after collection from the field in different years and seasons. Mean ± 2 SE.
Figure 4. The Kaplan-Meier estimated median survival duration, in days (±interquartile range) that each species survived when incubated under normoxia (21%) or hyperoxia (30%). Hashed lines indicate the duration of experiments for species for which the Kaplan-Meier estimator could not be calculated as most individuals survived until the experiment ended (censored observations). An asterix (*) indicates species with significantly different survivals under different oxygen treatments. For stability of incubation temperature see Table 1 and Figure S3 for the Kaplan-Meier estimation figures.
