SUBZERO TEMPERATURE TOLERANCE IN SPIDERS - ROLE OF THERMAL-HYSTERESIS FACTORS

The immature stages of 2 spp. of spiders (Philodromus and Clubiona) which overwinter under the bark of standing dead trees survive subzero temperatures by depressing their supercooling points in winter. The solutes which are at least partially responsible for the decrease in supercooling points in winter are: proteins which produce a thermal hysteresis (a difference between the freezing and melting points) of .apprx. 2.degree. C in the hemolymph and glycerol. The thermal-hysteresis-factors and glycerol are only found in the spiders in winter. Acclimation of winter spiders to warm temperatures, at either long or short photoperiods, results in loss of the thermal hysteresis within 2 wk. These thermal-hysteresis-factors appear to be similar to protein and glycoprotein antifreezes previously found in polar marine fishes and certain overwintering insects.