Upper thermal tolerance of early juveniles of six terrestrial hermit crab species:supplementary material

Abstract

Because temperature strongly influences biological\nprocesses of ectotherms, they must adapt to the thermal conditions of their\nhabitats. We evaluated the upper thermal tolerance of early juveniles of six\nterrestrial hermit crab species in the family Coenobitidae (genera Birgus and Coenobita), B. latro, C. brevimanus, C. cavipes, C. purpureus,\nC. rugosus, and C. violascens, that occur in the northwestern Pacific region of\nJapan. A total of 30 laboratory-raised juveniles (approximately 1 mm in shield length) carrying gastropod shells were\nindividually stocked in small plastic cups with sandy bottoms in\ntemperature-controlled incubation chambers at ~27°C. The temperature was increased by 1°C every 48 h, and the\njuveniles were observed until all the crabs had died. The median upper lethal temperature was estimated as the\ntemperature at which 50% of the test juveniles had died. The median upper\nlethal temperature estimates significantly varied among the species. Coenobita violascens, which mainly occurs\nin mangrove estuaries with lower thermal conditions, had the lowest median\nupper lethal temperature values. The median upper lethal temperature values estimated\nfor B. latro were slightly lower than\nthose for the other Coenobita species,\nprobably reflecting its cryptic nature in natural habitats during the juvenile\nstage. The most northerly distributed species, C. purpureus, had the highest median upper lethal temperature\nvalues, suggesting the existence of common physiological mechanisms that regulate\nboth upper and lower thermal tolerance abilities.