The speciation continuum and species relations between populations: in search of agreement between the theory and practice of systematics

From an evolutionary point of view, the achievement of species status by a group of populations is an ongoing process (except for rare cases of instantaneous speciation), during which isolated populations acquire traits and adaptations that minimize gene flow between them. However, depending on the group, the ways and timing of the gaining of reproductive isolation may be different. In such a complex group for systematics as small vipers (genus Vipera, subgenus Pelias), there are a number of problematic situations for species delimitation: the ability to form hybrids and hybrid populations between species, adaptive hybridization and hybrid speciation, and possible traces of reversed speciation, which indicate that complete and irreversible reproductive isolation may not be achieved at all. The effectiveness of reproductive isolation largely depends on external factors, mostly related to the range spatial structure, ecology of species in areas of sympatry, as well as climatic conditions and their changes, landscape dynamics, etc. The only species concept that allows to describe new species in the absence of reproductive isolation, recognizes the possibility of hybrid and reverse speciation — de Queiroz unified species concept — is practically unsuitable due to the need to consider as species a large number of isolated populations. Therefore, the solution is a conservative approach in practical taxonomy, which takes into account as a species criterion the ecological divergence of species, the possibility of their sympatric existence, which is usually achieved at 5% divergence of the mitochondrial cytochrome b gene. Stabilized hybrid populations occupying distinct ecological niche different from those of parental species also deserve recognition as species of hybrid origin. Not only species deserves to be protected, but also a distinguishable and diverged group of populations — Evolutionary Significant Unit (ESU) or subspecies in traditional taxonomy.

On the species independence of Carlina cirsioides Klokov (Asteraceae)

The systematic position and modern state of populations of the rare species of Ukrainian flora Carlina cirsioides Klokov (Asteraceae) are considered. Since this species is included into the Red Data Book of Ukraine (2009) and the European List of Globally Threatened Animals and Plants (1991), it is well-known for European botanists as an endemic of the Ukrainian flora. However, neither the authors of Flora Europaea (1976), nor monographers of the genus Carlina recognize Carlina cirsioides as a separate species. Comparative morphological, chorological, and coenotic analyzes does not allow Carlina cirsioides to be considered as a separate species, endemic and relic of the Ukrainian flora. According to morphological features, specimens from the plains of Ukraine are referred to the subspecies Carlina acaulis caulescens, which is distributed mainly in plain regions of Europe. Ecological and coenotic conditions of habitats of Carlina acaulis in the lowland part of Ukraine are different from its habitats in the Carpathians and Alps and are close to xerotherme grass communities with Carlina acaulis of plains of Central Europe. Steppe communities of Festuco-Brometea class with Carlina acaulis in the Volhynian-Podolian Upland are similar to xerotherme communities with Carlina acaulis of Central Europe. Erico-Pinetea class communities are common habitats for Carlina acaulis in the Ukrainian Polissia and north-eastern Poland. Lowering the species status of Carlina cirsioides from separate species to subspecies Carlina acaulis caulescens does not diminish its phytosozological value. Due to the low number of Carlina acaulis populations in the Volhynian-Podolian Upland and Polissia, all localities of this species in the lowland part of Ukraine need to be provided by protection.

Modern evolutionism and the views of A. A. Lyubishchev on the problem of species

With the advent of Darwinism, historical, functional, and adaptive approaches began to dominate in the theory of form. According to A. A. Lyubishchev: «Historical morphology devoured constructive». The tasks of morphology and taxonomy are closely related. Both disciplines should strive to identify the laws governing the diversity of the organic world. The nomogenetic component of evolution, the laws underlying the system, are reflected in morphology. And vice versa, the similarity of organs of different origins, facts of incomplete homology, pre-adaptation of forms, a huge number of parallelisms and many other morphological factors prove not only the existence of laws of form, but also the nomogenetic component of evolution. Despite the heterogeneity and exceptional complexity in the structure of organisms, there is a recurrence of similar forms that penetrates the entire systematics, suggesting that the forms of organisms are not epiphenomenons of a complex structure. An excellent example of regular variability is the Law of homologous series of hereditary variability by N. I. Vavilov: «knowing what mutational changes occur in individuals of any species, one can foresee that the same mutations in similar conditions will arise in related species and genera.» For A. A. Lyubishchev, the main components of evolution were: 1) tychogenetic (evolution based on random, unforeseen mutations); 2) nomogenetic (the presence of firm laws of development and limited form formation); 3) ectogenetic (factors external to organisms); and 4) telogenetic (active adaptation of organisms). At present, the study of architectonics and promorphology is coming to the fore, i.e. symmetry of organisms.

On the processes of sympatric speciation in the group of «yellow» wagtails in the Middle Volga region

This article discusses the mechanisms of sympatric speciation in the group of species of «yellow» wagtails based on hybridization. Interspecific and intraspecific hybridization can be attributed to the genetic mechanisms of divergence of populations of «yellow» wagtails. The existence of hybridization between the subspecies of the white-eared yellow wagtail M. flava beema and the yellow-fronted wagtail M. lutea leads to the emergence and further accumulation in the population of individuals with a light-colored head to varying degrees, the so-called «gray-headed» individuals. Intraspecific hybridization of subspecies forms of the yellow wagtail M. flava — nominative M. f. flava and white-eared M. f. beema leads to constantly occurring genotypic splits, which support intraspecific polymorphism of populations and provide the basis for further genetic divergence of these subspecies and species. The form of "gray-headed" hybrids is characterized by maximum genetic distances (1306.67–1375.67), which may correspond to the species rank. The modern polytypic complex of M. flava (in the narrow sense, a series of species and subspecies of only M. flava) probably formed in historical time on the basis of fan hybridization between the original forms of M. f. flava and M. lutea. Thus, the factors of genetic differentiation and divergence, along with ecological and geographical isolation, play a leading role in the formation of the spatio-temporal and genetic structure of the genus Motacilla. Currently, there is an active process of genetic divergence and separation of subspecies and species forms of «yellow» wagtails under conditions of wide sympatry within a single polytypic complex based on intraspecific and interspecific hybridization in the European part of Russia.

From species to cultivar and backwards

When one describes some plants, there are cases when natural selection produces cultivars, and the products of selective breeding appear to be species. The majority of specialists in fundamental and applied botany do not pay respective attention to this problem. Meanwhile, despite the formal following of the rules of respective Codes, there is a disregard to fundamental tenets of philosophy and mixing of natural and cultural objects. There is need to develop mechanisms that would prevent the conversion of species into cultivars and vice versa. The issue is considered on nomenclatural examples of taxa and culta of the genus Hedera.

Geographical distribution and species diagnostics of the Carboniferous and Permian genus Gzheloceras (Cephalopoda: Nautiloidea)

The article is devoted to an attempt to trace the ways of distribution of Late Paleozoic nautilids Gzheloceras Ruzhencev et Shimansky, 1954. The genus Gzheloceras Ruzhencev et Shimansky (Cephalopoda: Nautiloidea) includes a large number of species from Carboniferous and Permian sediments. Representatives of the genus Gzheloceras were distributed mainly in the northern hemisphere. They inhabited the warm epicontinental seas of the northern and north-western periphery of the Palaeo-Tethys. Species of the genus Gzheloceras differ from each other by insignificant differences in the position of the siphuncle, the details of the surface ornamentation, less often in the form of suture and the shape of the cross section of the whorls. The form of the conch and a transverse ornamentation indicate a nectobenthic lifestyle of the genus Gzheloceras. The centre of origin of the genus is the waters on the place of modern Kazakhstan. In the Serpukhovian or Early Bashkirian, representatives of the genus Gzheloceras, apparently, dispersed into the Urals. The genus Gzheloceras flourished in the Early Permian of the Urals.

The taxonomic complex Centaurea stoebe s. l. (Asteraceae) in the flora of Ukraine

Nowadays, many biological terms receive new interpretations, especially the concept of species. The species is the main structural unit of living things. It emerges, develops, and, when living conditions change either disappear or transforms into other species. There is no clear and unified definition of species. The achievements of contemporary molecular genetic studies indicate that the majority of microorganisms exist mainly not in a free-floating condition, but in formed associations or consortia. Microbial interactions occur by transferring molecular and genetic information, and various mechanisms such as secondary metabolites, siderophores, quorum-sensing system, biofilm formation, and cell transduction signals can be involved in this exchange. Therefore, for a deeper understanding of the concept of "species" in biology, it is necessary to take into account not only morphological and physiological criteria, but also to consider species from the viewpoint of systems biology, and to bear in mind factors of horizontal gene transfer. Therefore, the concept of "species" can be considered in a broader context, in particular within ecosystems with all assimilation relations.

Elusive species criteria and paradigms of botany

The development of botanical science and the improvement of methods used to identify the boundaries of species lead to constant changes in the criteria and volume of species in various systematic groups of plants. Currently, to solve these problems, modern methods of geno- and chemosystematics (for example, use of PCR, ITSS, and other markers), methods of discriminant and factor analyses, assessment of boundaries of ecological and climatic niches of different species, approaches of chemosystematics and metabolomics are used. However, the emergence of a large number of different modern approaches to estimate the volume of species has not simplified the task of plant taxonomists. Instead, it gave them the task to select or reasonably combine reliable methods. The latter would allow to progress in solving this difficult tasks and set priorities for the development of an integrated methodological approach to the study criteria and volumes of species.

On the position of parthenogenetic vertebrates in the evolutionary flow and the applicability of species concept to them

The review is devoted to the analysis of literature sources considering the concepts of "species" and its criteria, "speciation", "reticulate evolution" and "Darwinian evolution", "divergence", "hybridization", and "parthenogenesis". The evolutionary fate and place of parthenogenetic organisms (in particular, among vertebrates) in the general evolutionary flow are considered. The reasons for the predominance of bisexual reproduction despite the obvious energetic and quantitative benefits of parthenogenesis are analysed. The applicability of the term "species" to parthenogenetic organisms is considered, considering their discrepancy with the main (genetic and reproductive) species criteria according to most concepts.

Changes of knowledge of the fauna volume: species discovery curve in case of silken-fungus beetles of the Carpathians

The approach to the analysis of the fauna composition and completeness of its detection through the concept of “species discovery curve” is considered. Beetles of the family Cryptophagidae were taken as a model group. The dynamics of the accumulation of the information about the composition and volume of the Cryptophagidae fauna of the Ukrainian Carpathians during the eight stages of their study (the middle XIX, late XIX and the end of XIX century, the beginning of the XX century, the period until 1930–1940; middle and second half of XX century, and the current state for 1999 and 2021) are presented. In general, the composition of the cryptophagid fauna in the Ukrainian Carpathians is estimated at 116 species. This is 16 % more compared to what was known 100 years ago, i.e. each stage of the study adds about 5 % to the known species richness of this group of beetles. The components of fauna changes are analysed separately: 1) due to the changes in the nomenclature of existing species, 2) as a result of finding rare species (i.e. strengthening research efforts), 3) due to division or vice versa – combining existing species into two or three “small” species that were previously considered as morphs, varieties, or were not distinguished.