E.B. Lebedeva

A Unique Diploid-Tetraploid Unisexual-Bisexual Fish Complex (Pisces, Cobitidae)

The discovery of vertebrate clonal forms offered new prospects in evolutionary genetic, cytological, and ecological research, which can be divided into four major blocks: clonal form origin, cytogenetic mechanisms of clonal inheritance, clonal diversity and its sources, the ecological problems of the coexistence of clonal and bisexual forms. The important results of these studies were the following: clonal forms proved to have hybrid origin, the relationships between hybridization, unisexual reproduction, and polyploidy have been understood in the evolutionary respect. As a result, a concept of reticular speciation in vertebrates have been developed [1, 2] and the origin of even-polyploid species with restored bisexuality proved to be the final stage of this process [3, 4]. By now, about 80 forms were identified among fish, amphibia, and reptiles, which are reproduced by parthenogenesis, gynogenesis, and hybridogenesis. Unlike parthenogenesis that occurs in some groups of reptiles [5], natural gynogenesis involves males whose sperms stimulate egg development, although there is no true fertilization. Therefore, fish and amphibian gynogenetic forms inhabit the same areas as one or two closely related bisexual species from whose hybridization these forms have originated. In rare cases, the reproduction of clonal forms involves males of a third, less closely related, bisexual species. This way of clonal form reproduction leads to the development of unisexual–bisexual (clonal–bisexual) complexes, such as those indentified in the genera Poecilia , Poeciliopsis (Poeciliidae), Fundulus , Menidia (Atherinidae), Phoxinus (Cyprinidae), and Cobitis (Cobitidae) [2, 5, 6]. These complexes are diploid–diploid, diploid–diploid–triploid, and, in rare cases, diploid–triploid–tetraploid. In this study, we describe fish complexes from the genus Cobitis , in which the unisexual form is represented exclusively by tetraploid females.

The gynogenetic form of fish from the genus Cobitis (Cobitidae) in a region of its geographic range is monoclonal: DNA fingerprinting data.

Several dozens of unisexual fish species and forms, whose reproduction is brought about due to specific cytogenetic mechanisms, have been found by now [1, 2]. These species are represented by females only and are characterized by clonal or semiclonal inheritance based on natural gynogenesis, when females produce nonreduced eggs with genomes identical to the maternal one. After insemination, no true fertilization occurs, because sperms only stimulate egg development. In genetic terms, natural gynogenesis is indistinguishable from parthenogenesis. Reproduction systems differing from the bisexual one are found in fish of the genera Poecilia , Poeciliopsis , Menidia , Fundulus , Phoxinus , Carassius , Rutilus (Tropidophoxinellus), and Cobitis . The species and forms reproduced in the manner described above are combined with closely related bisexual species into complexes that are usually referred to as clonal-bisexual or diploid-polyploid complexes. The diploid species and hybrid forms are sometimes morphologically indistinguishable. We previously found a clonal-bisexual complex of Cobitis in the Moscow River near Zvenigorod [3]. This complex includes two diploid species ( C. taenia and C. melanoleuca ), a triploid form, and two tetraploid forms. The triploid genome (3 n = 74) contains the diploid number of chromosomes of an unknown species (2 n = 50) and the haploid number of C. taenia chromosomes ( n = 24). In one of the tetraploid forms, the genome of triploid form and the haploid genome of C. taenia were found. The triploid form is represented only by females that are reproduced by gynogenesis [4]. To date, the clonalbisexual complexes of fish of the genus Cobitis are found in many basins of Eastern and Western Europe [4 − 6]. Analysis of the clonal structure of the unisexual forms is an important line in studying the clonal–bisexual fish complexes. This report presents data on the clonal structure of the unisexual triploid form of Cobitis from the Moscow River that was determined for the first time using multilocus DNA fingerprinting. The monoclonal structure of triploid Cobitis from a locality of the Zvenigorod area of the Moscow River was confirmed using various restrictase/probe combinations. Adult individuals of the genus Cobitis that were ready for reproduction were caught in June 2002 in spawning grounds in the Moscow River near the Zvenigorod Biological Station of the Moscow State University. Fish ploidy was determined by the number of chromosomes and erythrocyte square. Thirty six gynogenetic Cobitis were selected for our analysis. The blood of adult individuals was sampled using EDTA as an anticoagulant. DNA was isolated from the blood by the standard phenol–chloroform method using proteinase K. DNA samples were treated with restriction endonucleases and analyzed by blot-hybridization with a [ 32 P ]-labeled probe [7]. Since the DNA-fingerprinting pattern depends only on the restrictase and the probe [8], we used the following restrictase/probe combinations: Bsu RI/(GACA) 4 , Mva I, Bsu RI/(TCC) 5 , Mva I/(CAC) 5 , Hinf I, Mva I/Jeffrey’s core 33.15, Hinf I, Mva I/(TCT) 6 , Bsu RI, Hinf I, Mva I/(GATA) 4 , Bsu RI, Hinf I, and Mva I/(CT) 9 . Nineteen fingerprinting patterns of triploid gynogenetic individuals, which were obtained using microsatellite probes (TCC) 5 , (CT) 9 , (TCT) 6 , and (GATA) 4 and various restrictases, are shown in the figure. Regarding the distribution of the fingerprinting pattern fragments, no differences were found between triploids of the populations studied; i.e., all of them represented a single clone. With all the above restrictase/probe combinations, identical patterns were obtained for 36 analyzed individuals. DNA fingerprinting was used in this study for the first time to determine the clonal origin of gynogenetic fish of the genus Cobitis . This is the most efficient method for detecting even minor interindividual genomic distinctions [8]. Our results testify to the genetic homogeneity of the group of Cobitis studied. These data differ from the evidence previously obtained [9] on the gynogenetic fish Poecilia formosa. Using GENERAL BIOLOGY

The karyological study in backcross hybrids between the sterlet, Acipenser ruthenus, and kaluga, A. dauricus (Actinopterygii: Acipenseriformes: Acipenseridae): A. ruthenus x (A. ruthenus x A. dauricus) and A. dauricus x (A. ruthenus x A. dauricus)

Many species of sturgeons have a high ability to form viable and more or less fertile hybrids by artificial crosses (Nikolukin 1972); the interbreeding between various combinations of sturgeon species was also observed in nature or assumed from some morphological and genetic data (Soldatov 1915, Berg 1948, Vasil′ev 1979, Birstein et al. 1997, Ene and Suciu 2001, Ludwig et al. 2002, 2009). The property of easy interspecific hybridization is widely used to produce sturgeon hybrid stocks with economically ACTA ICHTHYOLOGICA ET PISCATORIA (2014) 44 (4): 301–308 DOI: 10.3750/AIP2014.44.4.04

The karyotype of the Amu Darya sturgeon, Pseudoscaphirhynchus kaufmanni (Actinopterygii: Acipenseriformes: Acipenseridae)

The order Acipenseriformes is an ancient group of vertebrate animals represented by two fossil families: Peipiaosteidae, extending back to the Upper Jurassic, and Chondrosteidae, dating from the Lower Jurassic, and extant representatives in two families: Acipenseridae and Polyodontidae (see Findeis 1997, Nelson 2006). Both extant families have fossil records with Mesozoic dating. Most primitive and the oldest paddlefishes (Polyodontidae) are known from the Lower Cretaceous of China (Protopsephurus) and North America (Paleopsephurus) (Grande and Bemis 1991); the only two living freshwater species represent two distinct phylogenetic lineages and genera (Hilton 2004): Polyodon spathula (Walbaum, 1792) in United States and Psephurus gladius (Martens, 1862) in China. Both the oldest sturgeon (Acipenseridae) species dated back to the Late Cretaceous in Montana are treated as taxa with an uncertain position, namely plesion Protoscaphirhynchus Wilimovsky, 1956, insertae sedis, and plesion Priscosturion Grande et Hilton, 2009, sedis mutabilis (see Hilton et al. 2011). The phylogenetic relations and taxonomic states of recent 25 sturgeon species also are the subject of a long-term discussion. Usually, living Acipenserid fish are subdivided into two subfamilies. Some authors (Findeis 1997, Nelson 2006) ACTA ICHTHYOLOGICA ET PISCATORIA (2014) 44 (2): 111–116 DOI: 10.3750/AIP2014.44.2.04