Paradox of Extended Flows in Dynamena pumila (Linnaeus, 1758) Colonial Hydroid

Abstract

Colonial hydroids are used as a natural model of a number of fundamental biological processes, including the self-organization of systems, which is most clearly expressed in the operation of the distribution system. Functional integration of the colonial organism is performed by the moving of intracavitary fluid (hydroplasm) along a tubular body represented by sprouts and the stolons that connect them. Hydroplasm movement occurs due to independent pulsations of hydrants and tubular coenosarc and frequently looks chaotic. However, food particles in hydroplasmatic flows (HPFs) can pass through the stolon at distances commensurate with the colonial organism length for one HPF. The formation of such HPFs is paradoxical, since, as demonstrated by our studies, the pulsator volumes are much smaller than the volume of registered unidirectional HPFs. The article presents the results of the study of (a) HPF length; (b) transverse stolon pulsations in different stolon internodes (modules); (c) HPF rate along the stolon modules; and (d) volumes of the main pulsators (hydrants, coenosarc regions). Microvideo recording for 1–2 h with a magnification of 100 and frequency of 4 frames/s is the basic method of study. The objects of study are seven linear Dynamena pumila colonies of six to eight sprouts each grown on glass from primary sprouts. The HPF length was determined visually by scanning the colony under a microscope for 1–2 h every minute for 10–20 s. Regular powerful HPFs usually started from the primary sprout. According to visual recording, their length was from two to seven stolon modules (6–20 mm). However, HPFs coming from the primary sprout could fill no more than two stolon modules (according to its volume). Consequently, the resulting total continuous HPF is composed of several local HPFs. By means of calculations, it was demonstrated that “swept volumes” (the difference between the max and min volumes) of certain pulsators is much less than the local HPF volume. While the compression of one to two hydrants is enough to form the weakest local HPF, simultaneous compression of ten to twenty hydrants is required to create a powerful HPF. The obtained data can be explained based on the hypothesis on the hydraulic synchronization of independent pulsators and coordinated involvement in the creation of total HPFs of intermediate sprouts, which are entered by the flow on its path; this results in food movement along the colony over significant distances.