Experiments with four planarian species, Dugesia tigrina, Planaria vitta, Dendrocoelum lacteum, and Bdellocephala punctata, indicate that starvation retards the rate of regeneration.

The question whether starvation influences the rate of regeneration in planarians has been answered variously in the literature. Child (1911), Abeloos (1930), and Wolsky (1935) state that starved animals regenerate at a slower rate than fed ones, while Bardeen (1901) and Sivickis (1933) maintain that they regenerate equally quickly.

The question is important for various reasons, but mainly because the right answer should throw some light on the problem whether the physiological reserves necessary for regeneration are retained completely or at least more tenaciously than other body reserves. If they are not, the retarded regeneration of starved animals might help us to test several substances for their influence on the rate of regeneration.

In our experiments four species were used to ascertain whether the results of starvation were similar in different species. They were Dugesia tigrina, Planaria vitta, Dendrocoelum lacteum, Bdellocephala punctata. The animals were placed in Petri dishes, in most cases 10 in each, with 50 ml. tap-water; the water was renewed every day. The experimental conditions were as much alike as possible in all experiments. Great care was taken that the temperature was the same, 21°±1°, in the dishes with the starved animals and in those containing the non-starved controls. Regeneration started from a transverse cut just behind the eyes, in the anterior part of the time-graded regeneration field (Brøndsted, 1946). Regeneration of an animal was considered to be finished when both the black eye-spots could be seen at a magnification of × 25 in standard illumination. Only large and therefore presumably well-fed animals were used. This precaution is especially necessary in wild animals, where the nutritional state is not known.

Dugesia tigrina

This species has been kept in our aquarium for years. Normally the animals are fed calf liver twice a week. Two groups of 10 and 11 animals each were starved for 24 days. Two groups of 10 each from the well-fed stock served as controls. By 105 hours after decapitation the 20 controls had regenerated their heads completely. At this time only 15 of the starved animals had regenerated.

Planaria vitta

This species is also reared in our laboratory; it is fed enchytraeids and thrives very well on this diet. Some animals were starved 90 days, and their reduction in size was roughly estimated. Petri dishes with 10 fed and 10 starved animals were placed on a background of paper ruled in millimetres. The lengths of the animals when creeping was measured, and averaged 6.0 mm. for fed animals, 2·4 mm. for starved ones, indicating a reduction during starvation to about of the weight of fed animals. Two groups each of 10 such starved animals were used in the experiment, and two groups each of 10 well-fed animals served as controls. Planaria vitta is a rather small species. It is therefore difficult to cut individuals at exactly the same level: the cut may be located more posteriorly in the time-graded regeneration field in some animals than in others. This explains why the regeneration curves shown in Text-fig. 1 cover a rather long period of time, because regeneration is slower when a more posterior cut is made.

TEXT-FIG. 1.

Planaria vitta. Percentage of animals with eyes regenerated against time after operation.

TEXT-FIG. 1.

Planaria vitta. Percentage of animals with eyes regenerated against time after operation.

The experiment (Text-fig. 1) shows that the rate of regeneration of the starved animals lags considerably behind that of the controls, an equivalent percentage being reached about 30 hours later.

It should be mentioned that in the course of the regeneration process the controls reproduced asexually to such an extent that 30 buds were produced, whereas the starved animals did not reproduce asexually at all. The experiment is therefore interesting because it suggests that the materials necessary for both regeneration and asexual reproduction are first used for regeneration in starved animals. The problem of the interrelation between the two processes is under investigation in our laboratory.

Dendrocoelum lacteum

These animals were caught under stones on the shore of Lake Furesø near Copenhagen.

In one experiment 20 animals were starved in the laboratory for 14 days after their capture. They all regenerated completely after 117 hours, whereas the controis (also 20 animals but freshly captured) required 105 hours for all of them to regenerate.

In another experiment 40 animals were starved for 16 days in the laboratory before operation, and 40 animals operated on 2 days after their capture served as controls. Due to various circumstances completion of regeneration for all the animals was not observed. Nevertheless the result was clear, as shown in Text fig. 2. As in the previous experiment, the starved animals lagged behind in regeneration by 10–20 hours.

TEXT-FIG. 2.

Dendrocoelum lacteum. Percentage of animals with eyes regenerated against time after operation.

TEXT-FIG. 2.

Dendrocoelum lacteum. Percentage of animals with eyes regenerated against time after operation.

Bdellocephala punctata

This species was collected under stones on the shore of Lake Furesd together with Dendrocoelum lacteum. Twenty specimens were starved for 34 days in the laboratory (at about 20° C.) before operation. Three of these specimens died 1 day after operation. Twenty animals which had been kept without food for 14 days, at temperatures varying from 4° to 8 ° C., served as controls. Such starvation is very slight because of the decreased metabolism at such low temperatures. One specimen died 2 days after operation. Text-fig. 3 shows the result. The starved animals lagged behind the controls by 5 to 35 hours.

TEXT-FIG. 3.

Bdellocephala punctata. Percentage of animals with eyes regenerated against time after operation.

TEXT-FIG. 3.

Bdellocephala punctata. Percentage of animals with eyes regenerated against time after operation.

These experiments with four species strongly suggest that starvation retards regeneration.

The retardation is somewhat different in the four species. It seems to be more pronounced in Dendrocoelum than in Bdellocephala, although the two species are systematically more closely related to one another than to either of the two other species; this is also revealed by the fact that the time-graded field of head regeneration in the two species is nearly identical (Brøndsted, 1946). None the less Dendrocoelum is more sensitive to starvation than Bdellocephala, as shown by a faster diminution of body size (judged by eye; no measurements have been made). This is presumably due to the fact that the latter species is more sluggish than most planarians, whereas the former is rather lively.

It is difficult to evaluate the retardation of regeneration after starvation in Planaria vitta as compared to the other species, because its regeneration rate is so slow. The rather great difference between the time of regeneration of the starved and not starved animals may be due to the long regeneration time in general in this species.

The fact that the rate of regeneration is decreased by starvation is presumably due to some physiological deficiency resulting from starvation. This may appear surprising because planarians are known for their extraordinary ability to starve and nevertheless to retain their morphological integrity; this itself may well be called a sort of regeneration. It is reasonable to assume that an ordinary regeneration after damage of a normally fed animal has the chemical resources necessary for such a process, so to say, ready at hand. Obviously the resources are also present in the body of the starved animal, as is indicated by the fact that it does regenerate; but the retardation in regeneration rate might be explained on the assumption that some substances have been used up, or nearly so, during starvation, substances which require some time to be rebuilt. This gives us a possibility of investigating the problem as to what substances must be available in the animal if it is to regenerate at a normal rate. Experiments are in progress in this laboratory; a start has been made with ribo-nucleic acid (Brøndsted, A. & H. V., 1953).

My thanks are due to the Carlsberg Foundation, Nordisk Insulin Foundation, and the Kongstad Foundation for financial support, and to Mrs. A. Brøndsted for carrying out several of the experiments.

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