ARE MITOCHONDRIA SUBJECT TO EVOLUTIONARY TEMPERATURE ADAPTATION

Thermal tolerance and the respiratory properties of isolated red muscl e mitochondria were investigated in Oreochromis alcalicus grahami from the alkaline hot-springs, Lake Magadi, Kenya. Populations of O. a. gr ahami were resident in pools at 42.8 degrees C and migrated into water reaching temperatures of 44.8 degrees C for short periods. The maximu m respiration rates of mitochondria with pyruvate as substrate were 21 7 and 284natom0 mg(-1) mitochondrial proteinmin-l at 37 degrees C and 42 degrees C, respectively (Q(10) = 1.71). Fatty acyl carnitines (chai n lengths C8, C12 and C16), malate and glutamate were oxidised at 70-8 0 % of the rate for pyruvate. In order to assess evolutionary temperat ure adaptation of maximum mitochondrial oxidative capacities, the rate s of pyruvate and palmitoyl carnitine utilisation in red muscle mitoch ondria were measured from species living at other temperatures: Nototh enia coriiceps from Antarctica(-1.5 to +1 degrees C); summer-caught My oxocephalus scorpius from the North Sea (10-15 degrees C); and Oreochr omis andersoni from African lakes and rivers (22-30 degrees C). State 3 respiration rates had Q(10) values in the range 1.8-2.7. At the lowe r lethal temperature of O. andersoni (12.5 degrees C), isolated mitoch ondria utilised pyruvate at a similar rate to mitochondria from N. cor iiceps at 2.5 degrees C (30 natom O mg(-1) mitochondrial protein min(- 1)). Rates of pyruvate oxidation by mitochondria from M. scorpius and N. coriiceps were similar and were higher at a given temperature than far O. andersoni. At their normal body temperature (-1.2 degrees C), m itochondria from the Antarctic fish oxidised pyruvate at 5.5% and palm itoyl-DL-carnitine at 8.8% of the rates of mitochondria from the hot-s pring species at 42 degrees C. The results indicate only modest evolut ionary adjustments in the maximal rates of mitochondrial respiration i n fish living at different temperatures.