Influence of Food Consumption on the Functioning of the Pulsator-Reversible Transport System in Hydroids—An Idiographic Approach

The reaction of the pulsator-reversible transport system to feeding was studied in the colonial hydroid Dynamena pumila (L., 1758) (Leptothecata, Sertulariidae). The study is based on an in-depth individual analysis of the movement of hydroplasma in the stolon in three small D. pumila colonies of similar structure, which were kept under the same conditions. The colonies were fed with freshly hatched Artemia salina nauplii by dosed feeding in three variants: (a) feeding a proximal large maternal shoot from which the colony grew; (b) feeding two distal daughter shoots near the growth apex of the stolon; and (c) feeding three middle daughter shoots. The direction of hydroplasmic flows (HPF) was recorded in all modules of the colony stolon every minute for 90 min immediately after feeding, noting only the direction and saturation with food particles. Then, HPF in the stolon module closest to the maternal shoot was immediately recorded using time-lapse microvideo for 1.5–2 h. The study was repeated on the same colonies 20–28 h after feeding. It has been shown that the following parameters increased in all colonies after feeding: the length and duration of HPF, the maximum speed of HPF, and the volume of transferred hydroplasma by each HPF in total per unit of time; the duration of the resting phases decreased. The results indicate an increase in the intensity of colony integration after receiving a limited amount of food. At the same time, the hypothesis about the insufficiency of pulsations of a single shoot in providing transcolonial HPF was confirmed. Using the every minute scanning of the HPF by stolon modules, it was found that the movement of food particles along the colony from one end to the opposite end is provided not only by the pulsations of the shoots that received food, but also by all of the other shoots. The described mechanism of functioning of HPF also operates in the absence of food, although the volumes of the transferred hydroplasma are smaller in this case. The idiographic approach made it possible to identify individual differences in each parameter and to detect quantitative discrepancies in the results depending on the place where food was obtained in the colony. Simple averaging concealed these differences, which may be essential for understanding the multifactorial dependence of the functioning of the transport system in a modular organism, characterized by the uncertainty of the combination of many equivalent processes, for example,