EFFECTS OF TEMPERATURE ON MITOCHONDRIA FROM ABALONE (GENUS HALIOTIS) - ADAPTIVE PLASTICITY AND ITS LIMITS

The effects of temperature on mitochondrial oxygen consumption, membra ne fluidity and cytochrome c oxidase activity were measured for five s pecies of eastern Pacific abalone (genus Haliotis) found at different latitudes and tidal heights. Mitochondria were isolated from freshly c ollected individuals and from specimens that had been acclimated in th e laboratory to temperatures spanning the extremes of each species' kn own habitat temperature range. The temperatures at which Arrhenius plo ts of respiration rate of mitochondria from freshly collected abalone exhibited sharp breaks in slope were found to correlate with the habit at temperature at the time of capture of each species. Membranes isola ted from freshly collected abalone living at warm temperatures (Haliot is cracherodii and H. corregata) were significantly less fluid (as det ermined by the fluorescence polarization of the probe 1,6-diphenyl 1,3 ,5-hexatriene) than were membranes from species captured at cooler tem peratures (H. rufesens and H. kamtschatkana kamtschatkana). Laboratory acclimation significantly shifted the temperature of mitochondrial th ermal inactivation in an adaptive manner in the eurythermal species, H . fulgens, H. corregata and H. rufesens, but did not alter this proper ty significantly for mitochondria from the stenothermal species, H. k. kamtschatkana. Laboratory acclimation resulted in temperature-compens atory changes in membrane fluidity in all species except H. rufesens. The temperatures at which cytochrome c oxidase activity was inactivate d also shifted in an adaptive manner in some species. Acclimation of m itochondrial respiration, membrane fluidity and cytochrome c oxidase a ctivity occurred only over the ranges of temperature at which each spe cies is common, suggesting that there is a relationship between acclim atory ability and the biogeographical distribution of congeneric speci es.