Research Article |
Corresponding author: Eva Hnátková ( hnatkova@tf.czu.cz ) Academic editor: Ekaterina Gornung
© 2018 Eva Hnátková, Costas Triantaphyllidis, Catherine Ozouf-Costaz, Lukáš Choleva, Zuzana Majtánová, Joerg Bohlen, Petr Ráb.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Hnátková E, Triantaphyllidis C, Ozouf-Costaz C, Choleva L, Majtánová Z, Bohlen J, Ráb P (2018) Karyotype and chromosomal characteristics of rDNA of Cobitis strumicae Karaman, 1955 (Teleostei, Cobitidae) from Lake Volvi, Greece. Comparative Cytogenetics 12(4): 483-491. https://doi.org/10.3897/CompCytogen.v12i4.28068
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The karyotype of Greek cobitid fish Cobitis strumicae Karaman, 1955, from Lake Volvi, Greece, a representative of one of its two major intraspecific phylogenetic lineages, was analysed by means of sequential Giemsa-staining, C-banding, silver-staining, CMA3 fluorescence banding and also by in situ hybridization (FISH) with rDNA probe. The diploid chromosome number was 2n = 50, karyotype composed of 10 pairs of metacentric to submetacentric and 15 pairs of subtelocentric to acrocentric chromosomes. The nucleolus organizer regions (NORs) as revealed by Ag- and CMA3 staining and FISH were situated in the telomeric region of the fourth submetacentric chromosome pair. The chromosomes contained very low content of C-positive heterochromatin. No heteromorphic sex chromosomes were detected. This first karyotype report for any species of lineage Bicanestrinia Băcescu, 1962 shows a simple karyotype dominated by acrocentric chromosomes and possessing single NOR-bearing chromosome pair. Cytotaxonomic implications of this finding for the taxonomy of the genus Cobitis Linnaeus, 1758 are further discussed.
chromosome banding, NOR phenotype, FISH, rDNA, cytotaxonomy of Cobitis loaches
The genus Cobitis Linnaeus, 1758 attracted the interest of evolutionary biologists by producing several gynogenetic female-only lineages after hybridisation of species (
Recent phylogenetic studies (
This study reports on the karyotype and other chromosomal characteristics of Greek cobitid fish C. strumicae from population inhabiting Lake Volvi, Greece, analysed by means of sequential Giemsa-staining, C-banding, silver-staining, CMA3 fluorescence banding and by in situ hybridization (FISH) with 28S rDNA.
Ten males and two females were collected at the outlet of a thermal spring into Lake Volvi, Greece, by dip net and transferred alive to the laboratory. The examined specimens are deposited as voucher samples in the collection of the Laboratory of Fish Genetics, IAPG, CAS, Liběchov, under Accession Code CoS/97. Valid Animal Use Protocol was in force during study in IAPG (No. CZ 02386). Standard procedures for chromosome preparation followed
At least 25 Giemsa-stained or banded metaphases plates per individual were examined, most of them sequentially. Chromosomes were classified according to
Karyotypes of a male (a) and female (b) of C. strumicae from Lake Volvi arranged from sequentially Giemsa-stained (upper row) and C-banded (lower row) chromosomes; sequentially Ag-stained chromosome pair with positive signal is framed in (a) and (b); metaphase cells of C. strumicae after CMA3 staining (c) and FISH with rDNA probe (d) chromosomes bearing CMA3 and FISH signals are framed; m – metacentric, sm – submetacentric, st – subtelocentric and a – acrocentric chromosomes. Scale bar: 10 μm.
Chromosome counts from all 12 individuals revealed an invariable diploid chromosome number 2n = 50. The karyotype consisted of 10 pairs of metacentric (m) to submetacentric (sm) and 15 pairs of subtelocentric (st) to acrocentric (a) chromosomes (Fig.
FISH with 28S rDNA probe showed strong labelling of a single chromosomal pair (Fig.
CMA3 staining revealed the positive signal on the NOR-bearing pair only (Fig.
We examined chromosomes of C. strumicae by means of several banding methods detecting sites of major ribosomal DNA, i.e. sites of NORs (
Recent cytogenetic studies in fish (
Diploid chromosome number (2n), karyotype structure, i.e. number of chromosomes in the particular categories and especially number and location of NORs, i.e. NOR phenotypes, have proven useful for fish cytotaxonomy.
The species under study, C. strumicae, shares the diploid chromosome number 2n = 50 with most of the species karyotyped so far. Its karyotype dominated by uniarmed (acrocentric) chromosomes and lack of morphologically differentiated sex chromosomes is rather common among Cobitis loaches.
This study was supported by the project EXCELLENCE CZ.02.1.01/0.0/0.0/15_003/0000460 OP RDE and RVO: 67985904 (E. H., P.R., Z.M.,), Czech Science Foundation 17-09807S (L. Ch.) and (partly) by a Research network of the French Ministère de l´Education Nationale (C.O.- C.). The authors thank P.S. Economidis, T.T. Nalbant for valuable help, advices and stimulating discussions about diversity of Bicanestrinia loaches and M. Rábová, IAPG, Liběchov, for laboratory assistance. This study is the part of a series Cytogenetics of bisexual species and their asexual hybrid clones in European spined loaches, genus Cobitis (Cobitidae, Cypriniformes).