Range limits and thermal physiological adaptation of intertidal limpets belonging to the genus Nipponacmea

Abstract

ABSTRACT Nipponacmea fuscoviridis and N. radula are common intertidal species along China's coast and are characterized by divergent biogeographic patterns. In order to understand the effects of thermal stress on the distribution of these rocky shore species, the upper thermal limits and thermal safety margins of these two species were determined and compared. Thermal tolerance of the southern species N. fuscoviridis was higher than that of its northern congener N. radula: (1) the lethal temperature (LT50) of N. fuscoviridis (mean ± SD = 44.19 ± 0.34 °C) was higher than that of N. radula (42.44 ± 0.17 °C); (2) levels of the heat shock protein HSP70 reached maximum values at 40 and 42 °C in N. radula and N. fuscoviridis, respectively; (3) the temperatures at which hsp70 and hsp90 genes were induced (Ton) in N. fuscoviridis were higher than those of N. radula; and (4) Arrhenius breakpoint temperatures (ABTs) of cardiac performance of N. radula and N. fuscoviridis were 36.74 ± 1.27 and 36.84 ± 1.04 °C, respectively. With the consideration of environmental temperature, the maximum habitat temperature (MHT) of the northern species, N. radula, was close to its ABT and lower than its LT50. The MHT for the southern species, N. fuscoviridis, was much higher than its ABT and closed to its LT50. These results indicate that the southern species, despite its higher upper thermal tolerance limit, is living nearer to its lethal temperature and might be more sensitive to the increasing air and ocean temperatures in the face of climate change.