Morpho-functional role of muscular systems for the evolution of parasitic barnacles (Cirripedia: Rhizocephala)

Annotation

Parasitology is a complex scientific discipline, the main tasks of which is the study of morphology, life cycles of parasitic organisms and evolutionary adaptations associated with the transition to a parasitic lifestyle. The most interesting point is studying adaptations to parasitism of highly specialized organisms, strikingly different in structure from their free-living relatives. Rhizocephalans are good example of such animals. The only thing that indicates their belonging to crustaceans is their dispersing larva. During the transition to endoparasitism, rhizocephalans have lost almost all the traits characteristic for their free-living relatives. The body of an adult female is represented by two functional parts: the interna, a system of trophic rootlets located in the body cavity of the host, and the externa, a sacc-like reproductive formation carried outside the host's body. In adults, it is impossible even to determine the axis of the body, there are no traces of segmentation, the digestive tract, specialized excretory and circulatory systems. Moreover, the presence of a nervous system in rhizocephalans raises a question. Parasitic barnacles are also known for their significant influence on hosts. These parasites are capable of causing parasitic castration of decapods, often without destroying the tissues of the gonads themselves. Nevertheless, many aspects of the structure of rhizocephalans still remain unknown. Getting the fullest possible understanding of the anatomy and morphology of parasitic barnacles at the moment is especially relevant. In particular, it was only very recently that the members of the group first described the muscular system of some Rhizocephala. The new data obtained indicate the uniqueness of the muscular system in rhizocephalans. Thus, the general organization of the muscular system was strikingly different in the studied species. Peltogaster paguri is characterized by a spiral arrangement of muscle elements, while representatives of the family Polyascidae and Sacculinidae have a network of star-like muscular elements. It is important to note that such a muscular system is unique and does not have any analogous in animals. This is due to the fact that it is formed in rhizocephalans de novo, since the body of an adult female does not inherit any organ systems from the larva. The present project is aimed at studying and describing the muscular systems in representatives of various families of rhizocephalans. At the moment, members of the team have described extremely unusual muscular systems of representatives of two families of rhizocephalans, however, for most families, there is still no data on musculature. The results obtained will make it possible to understand better the evolutionary trends in this group and the biology of its various representatives. It is important to note that the origin of rhizocephalans is still a controversial issue. A comparative analysis of the anatomy of these animals, in particular the structure of the muscular system, will make it possible to get closer to understanding how parasitism developed in this group. The study of rhizocephalans is also important from a practical point of view, since their hosts are often important commercial species reared in aquaculture. In addition, rhizocephalans can serve as regulators of the abundance of those introduced species that damage ecosystems.

Expected results

During the project, a comprehensive analysis of the organization of the muscular systems in a number of species of rhizocephalan crustaceans belonging to different families will be carried out. With the use of light and confocal microscopy, data will be obtained on the general plan of the structure of the muscular system and the localization of muscle elements within the rootlets of the interna. Using the methods of electron microscopy, information about the ultrastructural organization of muscle elements will be obtained and the details of their structure will be clarified. The complex use of several methodological approaches will make it possible to reconstruct in detail the structure of the muscular system in the rootlets of the parasite. The results obtained will be combined with modern data from molecular phylogenetic studies, which will allow us to trace evolutionary trends among rhizocephalans and to make conclusions about the morpho-functional role of muscles. Based on the data on the organization of the muscular system in representatives of several species of parasitic barnacles from different families, an assessment of the variety of variants of the structure and the degree of development of the muscular system, which forms de novo at the definitive stages of development of parasitic barnacles, will be carried out. Since there have been almost no such studies previously, these new data will allow us to understand the mechanisms of nutrient transport along the rootlets of interna of rhizocephalans and the coherence between interna structure and the type of organization of the muscular system. The results obtained during the implementation of the project could also be useful for practical sources. Rhizocephalans are parasites of commercial decapod crustaceans, and the data obtained can be used in the development of measures to control rhizocephalans in aquaculture. In addition, a more complete understanding of the physiological features of rhizocephalans will make it possible to use them as a means of biological control for the introduced species.