Physiological Adaptation Of Mytilus-Edulis To Cyclic Temperatures

Mytilus edulis adapted to cyclic temperatures by reducing the amplitude of response of oxygen consumption and filtration rate over a period of approximately two weeks, and thereby increasing their independence of temperature within the range of the fluctuating regime. When acclimated to cyclic temperature regimes within the range from 6 to 20°C, the metabolic and feeding rates, measured at different temperatures in the cycle, were not significantly different from the adapted response to equivalent constant temperatures. Physiological adaptation ofMytilus edulis to different thermal environments was reflected in their metabolic and feeding rate-temperature curves. Animals subjected to marked diel fluctuations in environmental temperature showed an appropriate region of temperature-independence, whereas animals from a population not experiencing large diel temperature fluctuations showed no region of temperature-independence. In a fluctuating thermal environment which extended above the normal environmental maxima, respiratory adaptation occurred at higher temperatures than was possible in a constant thermal environment. The feeding rate was also maintained at higher temperatures in a cyclic regime than was possible under constant thermal conditions. This represented a shortterm extension of the zone of activity in a fluctuating thermal environment. The net result of these physiological responses to high cyclic and constant temperatures has been assessed in terms of ‘scope for growth’. Animals acclimated to cyclic temperatures between 21 and 29°C had a higher scope for growth at 29°C and were less severely stressed than those maintained at the constant temperature of 29°C.

A Possible Role Of Alpha-Amylase Isoenzymes From The Style Of The Mussel Choromytilus-Meridionalis (Krauss) Following Thermal-Acclimation

Separation of the proteins comprising the crystalline style of the mussel Choromytilus meridionalis (Krauss) by anion exchange chromatography shows that there are three fractions displaying α-amylase activity in both warm- and cold-acclimated mussels. These fractions correspond with one or more proteins which remain unbound to the resin (Peak I), a bound fraction which is eluted at 100–150 mM NaCl (Peak II) and a further fraction which is eluted at 200–250 mM NaCl (Peak III) but which may represent contamination carried over from Peak II. Cold-acclimation to 8°C results in the appearance of a fourth α-amylase fraction (Peak IV) which is eluted from the column between 300–400 mM NaCl. Thermal acclimation also results in changes in the activities of Fractions I–IV such that a specific activity of 0.47 mg glucose liberated per A280 unit of protein per 8 min incubation at 8°C in Fraction IV is increased nearly 10-fold to a specific rate of 4.10 in protein Fraction I following acclimation to 22°C. It is suggested that an increased of digestive activity may be of equal importance to a suppression of metabolic costs in the maintenance of energy flow into growth and reproduction in ectothermic organisms which experience an increase of environmental temperature, especially in bivalves such as C. meridionalis which do not show a compensatory increase in filtration rate.

Contrasting transcriptome response to thermal stress in two key zooplankton species, Calanus finmarchicus and C. glacialis

Climate change has already led to the range expansion of warm-water plankton assemblages in the northeast Atlantic and the corresponding range contraction of colder-water species. The temperate copepod Calanus finmarchicus is predicted to shift farther northward into polar waters traditionally dominated by the arctic copepod C. glacialis. To identify temperaturemediated changes in gene expression that may be critical for the thermal acclimation and resilience of the 2 Calanus spp., we conducted a whole transcriptome profiling using RNA-seq on an Ion Torrent platform. Transcriptome responses of C. finmarchicus and C. glacialis from Disko Bay, west Greenland, were investigated under realistic thermal stresses (at + 5, +10 and +15°C) for 4 h and 6 d. C. finmarchicus showed a strong response to temperature and duration of stress, involving up-regulation of genes related to protein folding, transcription, translation and metabolism. In sharp contrast, C. glacialis displayed only low-magnitude changes in gene expression in response to temperature and duration of stress. Differences in the thermal responses of the 2 species, particularly the lack of thermal stress response in C. glacialis, are in line with laboratory and field observations and suggest a vulnerability of C. glacialis to climate change.