Intraspecific physiological variability of the gastropod Littorina saxatilis related to the vertical shore gradient in the White and North Seas

Physiological responses to desiccation and temperature stress as well as be havioural responses to fast and abrupt environmental changes were investiga ted in high- and low-shore Littorina saxatilis (Olivi) from several populat ions from the White and North Seas. Variations in evaporation rates, resist ance to air exposure and to acute and chronic temperature stress between an imals from different shore levels were similar in White and North Sea periw inkles, consistent with the adaptive nature of these variations. High-shore snails were found to be able to conserve body water reserves better, to re sist higher temperatures and to survive longer under conditions of combined temperature and desiccation stress than their low-shore counterparts. In a temperature range of 25 to 35 degrees C, the rate of evaporative water los s was positively correlated with temperature in low-shore snails while bein g largely temperature-independent in high-shore snails. Median lethal time during air exposure in L. saxatilis was negatively but not linearly related to the temperature of exposure. In a temperature range of 30 to 38 degrees C, the resistance to heat exposure in air was only slightly dependent on t he temperature, with Q(10) = 1.4 for the median lethal time; the heat resis tance dropped drastically at temperatures above 38 degrees C, with Q(10) = 593.8. This suggests different mechanisms of temperature resistance in diff erent parts of the studied temperature range. In contrast, behavioural resp onse to extreme salinity fluctuations was not uniform in the high- and low- shore periwinkles from the White and North Seas, which may reflect specific environmental conditions at different shore levels in the two areas studie d. Observed physiological and behavioural variations are discussed from the viewpoint of different adaptive strategies employed by eulittoral and euli ttoral-fringe animals within populations of a single species.