Freeze tolerance in an arctic Alaska stonefly

Area of Science:

• Environmental Science
• Zoology
• Insect Physiology

Background:

• Most aquatic insects cannot survive subzero temperatures.
• The physiology of cold-tolerant aquatic insects is not well understood.
• Nemoura arctica is an arctic stonefly found in Alaska.

Purpose of the Study:

• To investigate the freeze tolerance and overwintering physiology of Nemoura arctica.
• To determine the survival rate of N. arctica nymphs at subzero temperatures.
• To identify the cryoprotective mechanisms employed by N. arctica.

Main Methods:

• Collected N. arctica nymphs from the Chandalar River, Alaska.
• Recorded natural streambed temperatures.
• Exposed nymphs to controlled freezing conditions in the laboratory.
• Measured hemolymph glycerol concentrations and analyzed ice-binding factors.

Main Results:

• N. arctica survived temperatures as low as -15°C, demonstrating freeze tolerance.
• Laboratory freezing of nymphs to -15°C for 2.5 weeks resulted in 87% survival.
• N. arctica produced significant amounts of glycerol and exhibited recrystallization inhibition.
• Low concentrations of ice-binding factors were detected, with typical hexagonal crystal growth.

Conclusions:

• Nemoura arctica is the first described freeze-tolerant stonefly species.
• The species employs physiological adaptations, including glycerol production, for overwintering.
• These adaptations are similar to those found in terrestrial freeze-tolerant insects.