COMMUNICATION IN THE BIOLOGICAL SCIENCES
Department of Biology
EXAMPLE OF DISCUSSION
Although these results were obtained under laboratory conditions, they still establish physiological limits in terms of EWL for efts and newts. The ability of red-efts to tolerate dehydration better than newts might be adaptive given the problem of water loss confronting terrestrial amphibians. Indeed, the ability to tolerate dehydration is probably the most widespread physiological adaptation to a terrestrial existence in amphibians as a group (Chew 1961).
With respect to previous findings, it is interesting to note that the CAP of red-efts is similar to that of some other terrestrial urodeles (Ray 1958) while tolerance to dehydration in newts parallels findings of Littleford et al. (1947) and Houck and Bellis (1972) for some of the more aquatic species of salamanders.
The observation that red-efts had higher rates of EWL than newts did not support the second hypothesis. The explanation for these findings may rest with differences in body size. As Table 1 shows, efts were on average considerably smaller than newts. Since rate of EWL in amphibians has been shown to be inversely proportional to surface area (Schmid 1965), smaller animals should lose water from their skin more rapidly than larger ones. That the slopes of the regressions of rate of EWL on body mass in efts and newts differ significantly (-0.664 and -0.382 respectively) suggests, however, that these two forms respond differently in the test chamber. In efts, a small increase in mass leads to a greater reduction in rate of water loss than the same increment produces in newts. Such a reduction in EWL might help to offset the water conservation problems experienced by these small, recently metamorphosed juveniles.
The most probable explanation for the lower mass-specific rate of EWL in efts is that mass alone is not as good a predictor of surface area as it is in newts. Newts, although generally cylindrical, have large dorsolaterally compressed tails consistent with their aquatic mode of locomotion. Efts are more streamlined and possess tails that are cylindrical (and tapering) in cross section. Although measurements were not actually made, it seems likely, therefore, that in specimens of equal mass, efts will have a lower surface area than newts and realize a concomitant reduction in rate of EWL.
In light of these findings, it might be instructive if surface areas could somehow be measured so that newts and efts with similar values could be compared. With such a procedure, one might determine if there were any differences in the abilities of the skins of these two forms to retard evaporative water loss.
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