Adaptive responses to temperature in homogeneously and heterogeneously acclimated crabs

Abstract

Walking leg closer muscle neuromuscular parameters were recorded electrophysiologically from homothermally and heterothermally acclimated Carcinus maenas (eurythermic) and Cancer pagurus (stenothermic). Homothermal (and immobilised) crabs of both species were acclimated to either 8 C or 22 C, whereas heterothermally acclimated crabs were acclimated to 8 C and 22 C coincidentally, exposing the animal's central nervous system (CNS) to either the warm (22 C) or cold (8 C) acclimation temperature. Thus, heterothermal acclimation exposes the CNS/endocrine system and one set of walking legs at one acclimation temperature, the contralateral walking legs are acclimated to the other acclimation temperature. This allowed an investigation into the CNS influence on the attainment of acclimation by walking legs. Comparisons of acclimation responses of the neuromuscular function of isolated walking legs from the same animal were done with respect to the walking leg and CNS acclimation temperatures experienced. Animals were acclimated for two weeks, recordings were taken of excitatory junctional potentials (EJP) etc., from dactylopodite closer muscle fibres when stimulated by the tonic motor axon over an experimental temperature range (6-26 C).The acclimation responses in homothermally exposed crabs of both species resulted in partial (Precht, type III) responses in resting potential, single and double pulse stimulated excitatory junctional potential amplitudes, these were interpreted as responses that allowed the maintenance of muscle function in the new thermal condition. With respect to long term thermal acclimation other electrophysiological parameters gave equivocal compensatory responses. Capacity acclimation responses were more complete in C.pagurus than C.maenas. In heterothermally acclimated animals resting potentials and EJP amplitudes revealed partial acclimation responses in a compensatory manner. Acclimation of heterothermally acclimated C.maenas and C.pagurus was determined to be independent of a CNS influence, indicating thermal acclimation was in response to the local tissue acclimation temperature.