Thermal acclimation, heat shock and photoperiod: Do these factors interplay in the adaptive responses of crab neuromuscular systems to temperature?

Abstract Evidence is reviewed demonstrating that the adaptive responses to temperature made by the walking leg neuromuscular system of crabs ( Carcinus maenas ) are in response to local temperature and not in response to hierarchical influences by the CNS and hormonal systems. Evidence is presented showing that the laboratory acclimation responses in muscle membrane resting potential (RP) do not predict the responses in seasonal acclimatized crabs, suggesting that additional environmental factors may have a role. No consistent effect of either short or long day photoperiod was found on muscle membrane RP in 8 or 22 °C acclimated crabs. However, short day data for RP were more hyperpolarised than those from long day particularly at temperatures above 17 °C. In 8 °C acclimated crabs short day exposure resulted in consistently higher EJP amplitudes than following long day exposure. In 22 °C acclimated crabs day length had a less marked effect, but short day appeared to alter the pattern of response to temperature towards that for 8 °C acclimated crabs. Photoperiod was shown to have an effect on muscle tension, particularly in 8 °C acclimated crabs. Long day as compared to short day exposure resulted in a higher force generated at temperatures below about 17 °C with a marked temperature dependency. In 22 °C acclimated crabs the difference between short and long day exposure was less marked but in this case the force generated was consistently greater following short day exposure. Thus photoperiodic effects may play a role in acclimatization. Heat shock (HS) increased CTMax of 8 °C acclimated Carcinus from 33.04±0.2 to 34.17±0.52 °C. Following heat shock closer muscle RP was more hyperpolarised but the temperature dependency of RP was unaltered from non-heat shocked controls, furthermore HS increased the temperature at which RP failed from 25.21±0.71 to 34.17±0.52 °C. The effect of HS on EJP amplitude was complex, at low temperatures it lowered EJP amplitude but at higher temperatures the amplitude was increased. HS also significantly raised the temperature at which EJP failed from 23.39±0.73 to 27.43±1.16 °C. Force generated by the closer muscle was dependent on acclimation temperature. Short day photoperiod increased force generation particularly in cold acclimated crabs. HS reduced force generation over the temperature range measured.