ИСТИНА

Публикация обзорной статьи

Revolutionary events in biology at the turn of the XX and XXI centuries led to the enrichment of the methodological Arsenal of evolutionary biology. While classical biology used the Haeckel triad of methods (comparative anatomy, embryology, and paleontology) to solve this problem, since the beginning of the 21st century, the phylogenetic triad method has been replaced by the phylogenetic tetrad method-comparative anatomy, evolutionary developmental biology ("evo – devo"), paleontology, and molecular phylogenetics. The problem of the origin of bilaterally symmetrical animals is one of the key problems of phylogenetics. The article discusses two trends that exist in modern literature. One of them connects the origin of bilaterally symmetrical animals with planule-like organisms that do not have a through gut, coelome, metamerica and have a shape similar to the modern representatives of the taxon Xenoacoelomorpha. Another point of view suggests that the ancestors of Bilateria had a complex organization, had a through gut formed by amphistomy, a coelom, metamerica, and possibly even metameric limbs. According to the second concept, the ancestors of Bilateria were bilaterally symmetrical coelenterates (i.e. bilayer organisms), similar to late Proterozoic metameric organisms. The latter concept suggests that Cnidaria and three-layered Bilateria are sister groups of organisms that had two circles of tentacles: labial and marginal. The marginal circle of tentacles in three-layered bilaterians gave rise to metameric limbs. The labial circle of tentacles in three-layered bilateria gives rise to the perioral ciliated tentacles and the ventral ciliated sole-neurotrochus. The problem of the General structure of the ciliated armament of pelagic Bilateria larvae is discussed. In Cnidaria, mesodermal genes are expressed in the annular region around the primary mouth. In three-layer bilateria, the mesoderm germ split into anterior and posterior, with the anterior associated with the pre – oral and tentacular segments, and the posterior associated with the trunk segments. Hox genes are expressed only in segments formed from the posterior source of the mesoderm. The perioral ciliated tentacles of Trochozoa are derived from the anterior tentacles of the labial circle and are always free of Hox gene expression. The article discusses the origin of Ecdysozoa, the uniqueness of their cuticle and primary bifurcated limb, the origin of the secondary bifurcated limb Crustacea, the homology of the lungs and trachea of terrestrial Arthropoda, and the wings of Hexapoda. The article provides a brief analysis of the organization of Cambrian and modern Lobopoda and the problem of transformation of the primary-bivalve limb of bivalves when adapting to life in a loose substrate. The transition to living in the thickness of the substrate led to a complete reduction of limbs in the Cambrian Palaeoscolecida, whose descendants are modern cephalorhynchus. A separate section of the article is devoted to discussing the role of progenesis (pedomorphosis) as a special direction of evolution of Bilateria. Progenesis played an important role in the evolution of Trochozoa. Arguments for the progenetic origin of Platyzoa are discussed. In the extreme form, this direction is expressed in Orthonectida and Dicyemida. A progenetic origin is assumed for Xenoacoelomorpha. This allows us to exclude Xenoacoelomorpha from the circle of possible ancestors of Bilateria. The problems of primary metamerism of Deuterostomia and the General patterns of expression of homeobox genes, from which the proboscis and collar segments are free, are considered. Taking into account the concept of inversion of body sides in chordates, labial tentacles give rise to radials of the median fin fold, while marginal tentacles give rise to radials of paired fin folds in primitive fish and fingers of Tetrapoda limbs. The expression of Hox11-Hox13 genes highlights the homology of Tetrapoda fingers to the radials of paired fins of sharks, lungfish, and sturgeon, and thus to the marginal tentacles of the common ancestors of Bilateria.

В статье обсуждается происхождение Ecdysozoa, своеобразие их кутикулы и первично-двуветвистой конечности, происхождение вторично-двуветвистой конечности Crustacea, гомологии легких и трахей наземных Arthropoda, крыльев Hexapoda. В статье дан краткий анализ организации кембрийских и современных Lobopoda и проблемы преобразования первично-двуветвистой конечности двуветвистых при адаптации к жизни в рыхлом субстрате. Переход к обитанию в толще субстрата привел к полной редукции конечностей у кембрийских Palaeoscolecida, потомками которых являются современные цефалоринхи. Отдельный раздел статьи посвящен обсуждению роли прогенеза (педоморфоза) как особого направления эволюции Bilateria. Прогенез сыграл важную рольв эволюции Trochozoa. Обсуждаются доводы в пользу прогенетического происхождения Platyzoa. В крайней форме это направление выражено у Orthonectida и Dicyemida. Прогенетическое происхождение предполагается для Xenoacoelomorpha. Это позволяет исключить Xenoacoelomorpha из круга возможных предков Bilateria.

Рассмотрены проблемы первичной метамерии Deuterostomia и общие для всей группы закономерности экспрессии гомеобоксных генов, от которой свободны хоботный и воротниковый сегменты. С учетом концепции инверсии сторон тела у хордовых лабиальные щупальца дают начало радиалиям медианной плавниковой складки, тогда как маргинальные щупальца дают начало радиалиям парных плавниковых складок примитивных рыб и пальцам конечностей Tetrapoda. Экспрессия генов Hox11-Hox13 подчеркивает гомологию пальцев Tetrapoda радиалиям парных плавников акул, двоякодышащих и осетровых рыб и тем самым – маргинальным щупальцам общих предков Bilateria.