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The Siberian wood frog survives for months underwater without oxygen - PubMed

  • ️Tue Jan 01 2019

The Siberian wood frog survives for months underwater without oxygen

Daniil I Berman et al. Sci Rep. 2019.

Abstract

Few of the amphibian species that occur in the Subarctic and in mountains are adapted to low sub-zero temperatures; most of these species overwinter underwater. It is believed that the distribution of the species that overwinter underwater can be limited by the low oxygen levels in waterbodies covered with ice. We show that the colonisation of the coldest areas of Northern Asia (to 71°N) by the Siberian wood frog (Rana amurensis) was facilitated by a unique adaptation, the ability to survive extreme hypoxia - and probably anoxia - in waterbodies during overwintering. The oxygen content in the overwintering waterbodies that we have studied in different parts of the range of this species fell to 0.2-0.7 mg/L without causing any large-scale mortality among the frogs. In laboratory experiments the R. amurensis survived for up to 97 days in hermetically sealed containers with water that contained less than 0.2 mg/L oxygen at temperatures of 2-3 °C, retaining the ability to respond to external stimuli. An earlier study of a broad range of frog species has shown that very few of them can survive even brief (up to 5-7 days) exposure to oxygen-free water. The revealed adaptation to prolonged extreme hypoxia is the first known case of this kind among amphibians overwintering in water.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1

Ranges of three species of brown frogs (Rana) against the background of isotherms of average absolute annual minima of air temperature in Northern Asia. The boundaries of ranges are constructed by us schematically according to the list of records and our data. The isotherm circuit is modified. Yellow dots indicate the localities where the material was collected.

Figure 2
Figure 2

Changes in levels of dissolved oxygen in the water in three series of experiments on the capacity of Rana amurensis to survive hypoxia (a) and records of the duration of survival under extreme hypoxia conditions. (b) Each line refers to one hermetic container with frogs; each flag indicates the death of one individual. Experimental series I and II are marked blue and red, respectively (six containers with 15 individuals and 14 containers with 28 individuals, respectively; the frogs were captured prior to overwintering in autumn 2016 and 2017); series III is marked purple (four containers with eight individuals collected in spring 2017 after overwintering). The duration of exposure of each individual to oxygen concentrations of at most 0.2 mg/L (days) is shown on a separate scale (b), with flags indicating the moments of death.

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References

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