The combined effects of temperature and salinity on the stomatogastric nervous system of two species of decapod crustacea.

Nervous systems must maintain coordinated activity patterns despite perturbations from unstable environmental factors (e.g., temperature, pH, and salinity). Marine organisms experience daily and seasonal changes in temperature while precipitation and ocean currents alter sea water salinity. We examined how the stomatogastric nervous systems (STNSs) from two species of decapod crustaceans (Cancer borealis and Homarus americanus) were affected by altered temperature and salinity. We used the patterned activity of the pyloric rhythm to assay the tolerance of the STNS to these two perturbations, independently and combined. The pyloric rhythm is generated by a well-characterized circuit containing a small number of identified neurons. These species exhibited distinct increases in rhythm frequency as temperature was increased, with the pyloric rhythm crashing between 25°C and 38°C. When salinity was increased to 1.25× that of the physiological (1×) saline, the pyloric rhythm crash temperature was ∼3°C-5°C lower in both species. Although the C. borealis pyloric rhythm crash temperature was similar between 1× and 0.75× salinities, in H. americanus, it crashed ∼3°C higher in 0.75× salinity. Although C. borealis and H. americanus share a common habitat, they exhibited differences in their responses to these perturbations. Despite each species having a similarly configured pyloric circuit, the order in which neurons crashed was species-specific. In summary, the C. borealis STNS was unaffected by salinity alone, but increased temperature and the combination of the two perturbations altered the pyloric frequency. In H. americanus, the pyloric frequency was affected by both perturbations individually as well as the combination of the two.NEW & NOTEWORTHY Here, we investigate whether or not multiple perturbations limit the ability of a nervous system to continue to function compared with when each perturbation is presented individually. This work demonstrates that different combinations of external perturbations can produce surprising consequences for circuit function that, in some cases, enhance circuit output and in other cases diminish it.