Low-temperature tolerance of early juveniles of six terrestrial hermit crab species: supplementary material

<p>Because temperature strongly influences biological processes of ectotherms, it also plays a fundamental role in determining their geographical distribution. We evaluated the low-temperature tolerance of early juveniles of six terrestrial hermit crab species in the family Coenobitidae (genera <i>Birgus</i> and <i>Coenobita</i>), <i>B. latro</i>, <i>C. brevimanus</i>, <i>C. cavipes</i>, <i>C. purpureus</i>, <i>C. rugosus</i>, and <i>C. violascens</i> that occur in the northwestern Pacific region, Japan. A total of 30 laboratory-raised juveniles (about 1 mm in shield length) carrying gastropod shells were individually stocked in small plastic cups with sandy bottoms in temperature-controlled incubatory chambers at ~27°C. The temperature was reduced by 1°C every 48 h, and the juveniles were observed until all the crabs had died; the median lethal temperature (MLT) was estimated as the temperature at which 50% of the test juveniles had died. The MLT estimates varied significantly among the species, and the most northward distributed species, <i>C. purpureus</i>, had the lowest MLT values. The phylogeny, paleoceanography, paleogeography, and paleoclimatology suggest that cooler thermal regimes might have acted as an evolutionary force for the divergence of <i>C. purpureus</i> in the Pliocene. A negative correlation was found between the northern latitudinal limit of distribution and the MLT values, even after controlling for the phylogenetic relationships in the six coenobitids. A temperature-dependent biogeography was thus recognized in terrestrial hermit crab species in the northwestern Pacific region, and global warming is expected to affect their geographical distributions.</p>