Abstract
All organisms live within a given thermal range, but little is known about the mechanisms setting the limits of this range. We uncovered cellular features exhibiting signature changes at thermal limits in Caenorhabditis elegans embryos. These included changes in embryo size and shape, which were also observed in Caenorhabditis briggsae, indicating evolutionary conservation. We hypothesized that such changes could reflect restricted aerobic capacity at thermal limits. Accordingly, we uncovered that relative respiration in C. elegans embryos decreases at the thermal limits as compared to within the thermal range. Furthermore, by compromising components of the respiratory chain, we demonstrated that the reliance on aerobic metabolism is reduced at thermal limits. Moreover, embryos thus compromised exhibited signature changes in size and shape already within the thermal range. We conclude that restricted aerobic metabolism at the thermal limits contributes to setting the thermal range in a metazoan organism.
Highlights
All organisms live within a given thermal range, beyond which growth and fecundity decrease (Portner et al, 2006)
We found that the thermal limits of C. elegans were of 12 ̊C and 25 ̊C (Figure 1A), and those of C. briggsae of 14 ̊C and 27 ̊C (Figure 1B), in line with the fact that C. briggsae usually lives in warmer climates than C. elegans (Prasad et al, 2011)
We do not know whether the observed relative reduction in aerobic capacity beyond both thermal limits as compared to within the thermal range contributes to increased lethality at those limits, our results show a clear correlation between these features
Summary
All organisms live within a given thermal range, beyond which growth and fecundity decrease (Portner et al, 2006). Too, tolerance to high temperatures is increased in an amphibian crab when the animal is in the air compared to when it is in water, reflecting the reduced cost of oxygen supply in air (Giomi et al, 2014), again supporting the OCLTT hypothesis Overall, these data suggest that thermal limits in complex organisms are characterized by a mismatch in oxygen supply and demand, which would result in reduced energy production and limit reproduction and growth (Portner, 2002; Portner et al, 2006)
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