Cold hardiness in the boreal adder, Vipera berus

Area of Science:

• Zoology
• Herpetology
• Physiology

Background:

• Freeze tolerance is a critical adaptation for reptiles overwintering in cold climates.
• The European adder (Vipera berus) is a widespread reptile in regions experiencing sub-zero temperatures.
• Understanding the freeze tolerance limits of young reptiles is important for assessing population viability.

Purpose of the Study:

• To investigate the freeze tolerance of newborn adders (Vipera berus) from East-central Sweden.
• To determine the survival rates and lethal temperatures associated with short-term and prolonged freezing exposure.
• To assess the role of blood glucose in freeze tolerance in this species.

Main Methods:

• Three controlled freezing experiments were conducted on newborn adders.
• Snakes were exposed to different freezing rates (fast/slow) and durations (2-3 hours vs. 22-30 hours).
• Blood glucose levels were measured and compared between frozen and unfrozen individuals.

Main Results:

• Ten out of eleven adders survived a short (2-3 hours) exposure to an average of -3.1°C.
• No snakes survived longer exposures (22-30 hours) at average temperatures of -4.8°C or -3.8°C.
• A significant but small increase in blood glucose was observed in frozen snakes, with a doubtful contribution to freeze tolerance.

Conclusions:

• Newborn adders exhibit very limited freeze tolerance, surviving only brief periods at temperatures around -3°C.
• Prolonged exposure to colder temperatures (-4°C and below) is lethal.
• Supercooling may aid winter survival, but careful selection of hibernation sites is likely the most critical factor for young adders.