Tuatara: Volume 2, Issue 1, March 1949
Loss of Memory in Salamanders at Metamorphosis
Loss of Memory in Salamanders at Metamorphosis.
Metamorphosis—alteration, often of a profound nature—occurs in the life-cycle of all but directly developing amphibians. The New Zealand frog Liopelma has a direct development, but most other frogs, and the newts and salamanders, undergo more or less metamorphosis in the transition from larval to adult forms. External change is obvious to anyone who has watched, even casually, a developing frog: the development of external gills and their later loss; growth of limbs; absorption of the tail; the straightening and shortening of the tightly coiled, larval intestine, and the growth of the adult jaws follow each other in orderly sequence. Among newts and salamanders, fundamental changes, although not so apparent as in the frogs, nevertheless do occur—external gills and tail fins are reduced and absorbed and adult colour markings are assumed.
There are, however, internal changes at metamorphosis no less profound, but less observed and certainly less understood, than those occurring externally. One of these changes, probably unrecorded until Major S. S. Flower in 1927 noted its occurrence in the European Spotted Salamander, is a complete loss of memory which coincides with the metamorphosis. Such loss of memory indicates change in the nervous system of this salamander at metamorphosis. Major Flower kept three newly-born salamanders in separate jars. By giving individual attention, all three soon became tame enough to show no fear when approached, would take proffered food, and after some weeks, would even call attention to themselves when hungry by active movements and sending out bubbles. As metamorphosis approached, appetites increased, and the animals would freely swim to his hand and take earthworms.
Metamorphosis is complete, Flower says, when the larval gills disappear. This occurred on different days for each of the three salamanders. Although the environmental conditions were quite unchanged, all memory of their human attendant was lost in each case on the day of metamorphosis. Close approach to the jars frightened the animals; they tried to avoid capture by the hand and struggled wildly if picked up, they would not feed. A process of re-taming, taking several weeks, had to be undertaken, as though they were freshly-caught wild animals.
Flower's work points to an interesting and little known aspect of the metamorphosis of amphibians, an aspect that might well repay further study.
FLOWER, S. S., 1927. Loss of memory accompanying metamorphosis in Amphibians. Proc. Zool. Soc. London, 1927, 155-156.