Abstract
Homarus americanus, the Maine lobster, survives well in sea water at temperatures ranging between 10° and 20°C. Survival time is limited, however, if the water temperature is raised to 26°C or cooled to 3°C. At these temperature extremes the simple reflex responses disappear, and the animal becomes quiescent. The effects are irreversible in a very short period of time. The spiny rock lobster, Panulirus interruptus, an inhabitant of southern waters, is quite at home in sea water at temperatures of 35° or even higher. Several specimens have been maintained in well aerated sea water at 36° for several days in the laboratory aquarium. Moreover, a number have survived for weeks at temperatures as low as 10–12°. The lower limit, lethal range, for this southern species is about 7° and the upper limit about 38°C. When subjected to these temperature "extremes," Panulirus exhibits similar reactions to those of the northern variety. The disappearance of simple reflex responses in the limiting temperature ranges suggests that either nervous transmission is blocked or muscle contraction impaired, or both. If so, there is no question that these neuromuscular effects take place with warming at a far different (lower) temperature for Homarus than for Panulirus. To determine the cause of this temperature tolerance difference a comparative study of the effect of temperature on the single motor axons of both Homarus and Panulirus has been started. The first data obtained are described here and reveal a very definite species temperature sensitivity difference in the warming range. Methods. Motor axons were isolated from the meropodite segment of the walking limb of both Homarus and Panulirus and mounted in pairs, one from each species, across 4 platinumized-platinum electrodes (100–150 μ thickness) in Homarus physiological solution adjusted to pH 7.6(7).
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