Hidden Morphotypes and Homologous Series in Phenotype Variations in the Colonial Hydroids Dynamena pumila, Diphasia fallax, and Abietinaria abietina (Hydrozoa, Leptothecata)

Abstract

The intraorganismal variability of the shoot modules of three species of hydroids was studied to determine the degree of similarity between them. The strict form of the internodes (modules) of the shoots is repeated many times, which is useful for the study of intraorganismal variability. Against the general background of the high stability of the shape of the internodes, we found significant deviations from the norm. Some resemble the structure of the internodes in other genera of the same family. Their morphogenesis is different from that characteristic of the studied species. Most of the anomalies were characterized by stable forms and low frequencies of occurrence (<0.2%). After the appearance of abnormal internodes, normal ones were found to usually re-form. Thus, it is doubtful that the anomalies were caused by mutations. There is also no reason to believe that the anomalies were caused by environmental factors, since they always formed singly along with normal shoot modules of the same modular organism. In Dynamena pumila, Diphasia fallax, and Abietinaria abietina, the composition of their morphovariations was found to be similar, and their frequencies were comparable, which confirms the assumption that several latent phenotypes can be formed indeterminately based on one genotype. The study was conducted on samples of >20,000 internodes of each of the three species.