Published online by Cambridge University Press: 11 May 2009
Measurements during autumn and winter of the lower median lethal temperature of the barnacle Balanus balanoides (L.) under natural and modified environmental conditions in field and laboratory, show that the cold resistant state is advanced by three factors: short day photoperiod, reduced food assimilation and reduced temperature. Their relative efficacy is in that order.
These factors combine in promoting breeding and the acquisition of the cold tolerant state during autumn and winter. Although normally associated, breeding and cold tolerance are not mutually dependent; the one can be induced without the other under abnormal conditions.
Similar measurements made in the spring show that only a single factor is required to terminate the cold tolerant state — resumption of food assimilation. If feeding is discontinued in the spring, however, the cold tolerant state tends to return, but animals that have bred do not breed again until the following autumn.
Of the three well established mechanisms for seasonal cold tolerance — production of substances to cause freezing hysteresis, production of cryoprotective agents, and nucleating agents to promote freezing in the intercellular compartment — only the last can be entertained since the cold tolerant animal survives some 80% of the body fluids being converted to ice. The cold tolerant condition may also relate to higher levels of polyunsaturated fatty acids being present in the membrane lipid fraction in winter, so rendering cell membranes less prone to damage by ice crystals.
The suggestion is made that normal metabolic activity and tolerance of low chemical potential of water - the common factor in freezing and desiccation - are not compatible.