Phenotype of healthy and tumoral hydras from the clonal strains of St. Petersburg. (A) Healthy hydra from the tumor-free strain: the body is long and thin, and the number of tentacles does not exceed 7. (B) Tumoral hydra from the tumoral strain: many tumefactions thickening the body, and the tentacles are supernumerary (i.e. equal or superior to 8). The pictures are taken with a trinocular magnifier, scale bar: 1 mm.

Phenotype of healthy and tumoral zebrafish. (A) Healthy zebrafish from the AB strain. (B) Zebrafish with nevi (i.e. premalignant lesions) from the kita-GFP-RAS transgenic strain: the pigmentation pattern is altered. (C) Zebrafish with nevi and tumor from the kita-GFP-RAS transgenic strain: in addition to the modified pattern, a melanoma has developed on the fish’s back.

Graphical summary of the general experimental design.

The effects of four diets on tumorigenesis in hydras from tumoral and tumor-free St. Petersburg strains. (A) The proportion of juvenile hydras from the tumor-free strain developing spontaneous tumors across time (days) according to the diet followed. (B) The proportion of juvenile hydras from the tumoral strain developing tumors across time (days) according to the diet followed. (C) The frequency of the intensity of tumor phenotype expression in juvenile hydras from the tumoral strain according to the diet followed. (D) The proportion of five-week-old hydras from the tumor-free strain developing spontaneous tumors across time (days) according to the diet followed since their fifth week. (E) Changes in the frequency of the intensity of tumor phenotype expression in hydras from the tumoral strain (five-week-old) according to the diet followed over one month (i.e. after tumor development).

The proportion of wild hydras developing tumors across time (days) according to diet.

The effects of four diets on tumorigenesis in zebrafish from the tumoral strain. (A) The proportion of juvenile zebrafish from the tumoral strain developing nevi across time (days) according to the diet followed. Given the high natural mortality (see “Materials and methods”), the analysis was performed only on individuals still alive at the end of the study or having developed nevi before dying. (B) The proportion of zebrafish with nevi from the tumoral strain developing tumors across time (days) according to the diet followed since their third month (i.e. after nevi development).