Paper on repeated freezing and thawing in JEB


In a recent paper published in Journal of Experimental Biology Karina Fisker measured the metabolic rate of encytreids exposed to repeated freeze thaw events and compared these to animals exposed to continuous thawed or frozen state. Although similar questions have been addressed in other organisms, this is a unique study in the sence that it investigates these responses in populations that are likely to meat very different winter conditions, including differences in freeze thaw events.

The main finding of this study was that freezing causes metabolic depression, but that freeze thaw events are not in associated with considerable energetic costs. Moreover we found that the tolerance to continuous freezing was markedly higher in arctic populations, while the tolerance to freeze thaw events was more similar between temperate and arctic populations of encytreids 

Fisker, K.V., Holmstrup, M., Malte, H. and Overgaard, J. (2014)

Effect of repeated freeze-thaw cycles on geographically different populations of the freeze tolerant worm Enchytraeus albidus (Oligochaeta).

The Journal of Experimental Biology 217:3843-3852


Drosophila Cold Tolerance Paper in Functional Ecology

The paper "How to assess Drosophila cold tolerance: chill coma temperature and lower lethal temperature are the best predictors of cold distribution limits" is now avaliable online.

  Five metrics of cold tolerance were measured for 14 Drosophila species to determine which metrics most strongly correlate with geographic distribution. Measures of chill coma onset temperature, lethal temperature and lethal time at low temperature proved to be the best predictors to describe the variation in realized latitudinal distributions and estimated environmental cold exposure. Measures of chill coma recovery time also correlated significantly with estimated minimum temperature, while the supercooling point did not.

Considering the findings of the present study, data from previous studies and the logistical constraints of each measure of cold tolerance, we conclude that chill coma onset temperature and lethal temperature are superior measures when estimating the ecologically relevant cold tolerance of drosophilids. Of these two traits, chill coma onset temperature requires less equipment, time and animals and thereby presents a relatively fast, simple and dynamic measure of cold tolerance.



Paper on rapid cold hardening published in JIP

In a recent paper published in Journal of Insect Physiology we describe the physiological and transcriptional changes occurring during RCH in Drosophila. In a rare attempt to cover several orders of biological organization we study RCH at the level of transcription, protein translation and try to associate these changes to activity of up-regulated proteins and their resulting metabolites.

The main finding of the study was that increased abundance of a single protein glycogen phosphorylase was associated with increased levels of glucose, but interestingly, these changes were not associated with increased transcription of GP transcripts or of increased GP activity when measured at the level of the protein.


The rapid cold hardening response of Drosophila melanogaster: Complex regulation across different levels of biological organization

Johannes Overgaard, Jesper Givskov Sorensen, Emmanuelle Com, Herve Colinet

Upper thermal limits in digesting snakes is not limited by oxygen transport capacity

In a recent short paper published in Journal of Experimental Biology we investigated metabolic rate during fasting and digestion on ball pythons when exposed to critically high temperatures. According to the OCLTT hypothesis it could be hypothesised that the additional metabolic costs associated with digestion (an almost 4 fold increase in metabolic rate) would render the snakes more vulnerable to high temperatures. However the data showed that snakes maintained a considerable aerobic scope even at temperatures approaching the leathal level and while some snakes regurgitated at these high temperatures the evidence suggested this was not associated with limited aerobic capacity.

Fobian, D., Overgaard, J. and Wang, T. (2014)

Oxygen transport is not compromised at high temperature in pythons.

The Journal of Experimental Biology 217:3958-3961


New paper published in Global change biology.

Sensitivity to thermal extremes in Australian Drosophila implies similar impacts of climate change on the distribution of widespread and tropical species

Global Change Biology

we demonstrate that it is especially the extreme temperature events that define the distribution ofAs climate change is progressing, the temperature of our planet increases. This is particularly important for the large group of animals that are cold-blooded (ectothermic), including insects. Their body temperature is ultimately determined by the ambient temperature, and the same therefore applies to the speed and efficiency of their vital biological processes. But is it changes in average temperature or frequency of extreme temperature conditions that have the greatest impact on species distribution? In a recent recent publication in the journal  both tropical and temperate drosophila species. Thus climate change affects ectotermic animals primarily because more periods of extreme weather are expected in the future.

Linkt to paper:

See also the news links below: (English)  (Danish) (Danish)

Paper published in Journal of Insect Physiology

JIPIn this study we describe a method for obtaining reliable estimates of standard metabolic rate for small ectothermic animals. Using repeated stop-flow respirometry we were able to investigate the effects of inbreeding on standard metabolic rate in Drosophila melanogaster. We hypothesized that inbreeding results in increased metabolic rate, and further that this effect would be more pronounced at stressful low and high temperatures. However, contrary to our hypothesis we did not find any interaction between temperature and the effect of inbreeding or any general difference in metabolic rate between inbred and outbred individuals. However, inbreeding did affect the variance. Nonetheless variance in metabolic rate was higher between the inbred lines compared to the outbred lines with some inbred lines having very high or low metabolic rate, indicating that genetic drift, and not inbreeding, seem to explain the variation in metabolic rate in populations of different size.


Paper published in Journal of Comparative Physiology B

image001In this study we found that cold tolerance in Enchytraeus albidus was varied in a reliable manner with location from where the populations originated such that cold adapted arctic populations were more cold resistant than populations from temperate environments. Glucose accumulation, glycogen reserves and metabolic rate also varied significantly between populations but this variation was not related directly to cold tolerance suggesting that the metrics important for cold tolerance are complicated. When measuring metabolic rate of frozen and unfrozen animals at the same temperature (-2°C) we found a metabolic depression of approximately 50%. Interestingly this depression was larger in the arctic than temperate population suggesting that frozen artic animals may have lower energetic turnover than temperate conspecifics.