Non‐budding strains of hydra: Isolation from sexual crosses and developmental regulation of form

Abstract New strains of hydra were obtained from sexual crosses; 15% of these strains exhibited impaired or no budding. Altered tentacle number, regeneration, size and form almost always accompanied this non‐budding trait. Strains selected for deficient budding activities were also more variable in morphology than are normal hydra. Two developmental traits were studied in the non‐budding animals; regenerative ability and the formation and control of supernumerary tentacles. The regeneration patterns of non‐budding hydra vary with the size of the piece of regenerating tissue. Column segments greater than 3 mm in length regenerate hydranths at all cut surfaces, whereas pieces less than 1 mm long usually regenerate bases at proximal surfaces, as do normal animals. When polyps grow abnormally long, they form supernumerary tentacles. Formation of these tentacles seems to be normally suppressed by a nearby hydranth. Supernumerary tentacle formation can be suppressed even in long, non‐budding hydra, by implants of hypostomal or subhypostomal tissue. The non‐budding hydra phenotype appears to result from developmental lesions spread throughout the polyp body. Budding is one of the primary aspects of development which is affected, and a lack of budding leads to increased animal size. This in turn results in many pleiotropic effects including supernumerary tentacle formation and altered regeneration patterns.