A fitness cost for thermal tolerance in a marine copepod: Implication on biological effects of global warming

Abstract

On rocky shores, the marine copepod Tigriopus japonicus is an inhabitant of shallow supralittoral tidepools and able to cope with a certain degree of thermal stress. However, different geographical populations of T. japonicus may have different extents of thermal tolerance. This study used a two‐generation experiment to compare the thermal tolerance of a temperate South Korean population (SK) and a tropical Hong Kong population (HK) of T. japonicus. 81 mate‐guarding pairs (F0; 27 pairs each) were raised in three temperatures: 15, 20 and 25°C for 30 days. The first brood of each female was cultured in the same medium and their offspring were crossed with others exposed to the same temperature. The results showed that F0 of SK copepods demonstrated a lower lethal temperature (LT) at 42.9°C than F0 of HK copepods (LT: 45.3°C). At 25°C, although F1 of SK copepods showed an improved thermal tolerance, their reproductive output was significantly less than that of the HK's F1 group. Also, expression of heat shock proteins in the SK group was significantly higher than that in HK group after heat stress at 30°C for 90 minutes. Our results suggest that multigenerational development of thermal tolerance in SK copepod is possible, but at the expense of population fitness. Such observations have profound implications on the long‐term biological consequence of global warming on T. japonicus populations along the Western Pacific coasts.