Respiration rate and oxy-regulatory capacity in cold stenothermal chironomids.

The effects of temperature and oxygen saturation on the respiration rate of two cold stenothermal chironomids, Diamesa insignipes and Pseudodiamesa branickii were investigated. Fourth instar larvae were collected in winter in a glacio-rhithral stream (1300 m a.s.l., Alps, NE-Italy) and their respiration rate was measured with a Clark's electrode in the range 0-14 degrees C. The respiration rate was significantly higher in D. insignipes than in P. branickii at low temperatures (<or=4 degrees C), higher in P. branickii between 8 and 12 degrees C and comparable at 14 degrees C. Higher values of R (regulation value), R(25%) (respiration rate at 25% oxygen saturation) and b(1)/b(2) (slope ratio in piecewise linear regression), and lower values of P(c) (critical pressure) and I (initial decrease) were recorded in P. branickii than in D. insignipes. These values are compatible with oxy-regulatory behaviour in P. branickii, whereas D. insignipes appeared to be almost an oxy-conformer. On the basis of this autoecological information, new implications regarding survival of species from cold, high altitude habitats under changing climatic conditions are made.