No evidence for slow-down of molecular substitution rates at subzero temperatures in Antarctic serolid isopods (Crustacea, Isopoda, Serolidae)

The molecular slow-down hypothesis suggests a temperature-controlled slow-d own of molecular substitution rates to be a common characteristic of polar poikilotherm organisms. There is evidence that metabolic rate may be contro lling the rate of nucleotide substitution in many organisms. In this study, absolute rates of nucleotide change based on a geologically calibrated mol ecular clock from the 16S ribosomal RNA (LSU) gene of 12 species of serolid isopods living in Antarctic waters are calculated and compared with data f rom sesarmid crabs from tropical latitudes. Contrary to the prediction, no difference of molecular substitution rates between Crustacea from different latitudes can be detected. This result is corroborated by testing the rela tive rate in serolid isopods against other Crustacea from tropical, tempera te and Antarctic waters. While an influence of temperature on the rate of s pontaneous mutation cannot be dismissed, the results show that temperature is not the key determinant of the rate of nucleotide change as has been sug gested by the molecular slow-down hypothesis.