Research Article |
Corresponding author: Desislava Stoianova ( d.st.stoianova@gmail.com ) Academic editor: Natalia Golub
© 2015 Desislava Stoianova, Snejana Grozeva, Nikolay Simov, Valentina Kuznetsova.
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:
Stoianova D, Grozeva S, Simov N, Kuznetsova V (2015) Achiasmate male meiosis in two Cymatia species (Hemiptera, Heteroptera, Corixidae). In: Lukhtanov VA, Kuznetsova VG, Grozeva S, Golub NV (Eds) Genetic and cytogenetic structure of biological diversity in insects. ZooKeys 538: 95-104. https://doi.org/10.3897/zookeys.538.6722
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The karyotype and male meiosis, with a particular focus on the presence or absence of chiasmata between the homologs, were studied in the water boatman species Cymatia rogenhoferi (Fieber) and C. coleoptrata (Fabricius) (Corixidae, Cymatiainae). It is shown that the species have 2n = 33 (28A+2m+X1X2Y) and 2n = 24 (20A+2m+XY) respectively, post-reduction of sex chromosomes, and achiasmate meiosis of an alignment type in males. Cytogenetic and some morphological diagnostic characters separating Cymatia Flor from the rest of Corixidae are discussed.
Karyotype, m-chromosomes, sex chromosome post-reduction, spermatocyte meiosis, morphology, Nepomorpha , Corixoidea
The Corixoidea, known as water boatmen, are moderately large to small aquatic insects, belonging to the true bug infraorder Nepomorpha. According to
In meiosis, the chiasmata are known to tie homologous chromosomes together until their separation in the reductional division. However, in some animal groups, instead of chiasma formation, an achiasmate type of meiosis is observed, being, as a rule, restricted to the heterogametic sex (
In the present paper, the karyotype and male meiosis of other two Cymatia species, C. rogenhoferi (Fieber, 1864) and C. coleoptrata (Fabricius, 1777), were studied. The focal point of this work was to clarify the presence or absence of chiasmata in spermatocyte meiosis of these species.
Five males of Cymatia rogenhoferi and two males of C. coleoptrata were collected by light trap and hydrobiological net in different localities (Table
Species | Number of analysed males | Locality and date of collection |
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Cymatia rogenhoferi | 5 | Kazakhstan, Taukum Sands, near Topar River, eastern from Topar Village, 363m a. s. l., 45°02’12"N, 074°58’33"E, light trap, 31.05.2015, leg. N. Simov and F. Konstantinov |
C. coleoptrata | 1 | Bulgaria, Danube River, marsh Malak Preslavets, 20m a. s. l., 44°05'43"N, 026°50'23"E, 13.07.2014, leg. D. Stoianova |
C. coleoptrata | 1 | Bulgaria, Danube River, Srebarna lake, 13m a. s. l., 44°06'47"N, 027°03'34"E, 12.07.2014, leg. D. Stoianova |
The chromosomes were analysed under light microscope (Axio Scope A1 – Carl Zeiss Microscope) at 100× magnification and documented with a ProgResMFcool – Jenoptik AG digital camera. All preparations and remains of the specimens are stored at the Institute of Biodiversity and Ecosystem Research (IBER), BAS in Sofia, Bulgaria.
The testes of the adult males were full of sperm, with a small number of well-synchronised dividing cells. No spermatogonial metaphases were observed. When condensing from a diffuse stage (Figs
Male meiosis in Cymatia species. 1–3 C. rogenhoferi: a–c early condensation stages 2MI from the pole. The bivalents (consisting of two side-by-side aligned chromosomes facing the opposite poles) and three univalent sex chromosomes (two X and one Y) form a ring, with a pair of very small and negatively heteropycnotic m-chromosomes in its centre 3 MII. The autosomes and m-chromosome form a ring, with pseudo-trivalent of the sex chromosomes in its centre 4–7 C. coleoptrata: a, b early condensation stages 5MI from the pole. The bivalents (consisting of two side-by-side aligned chromosomes) and two univalent sex chromosomes (X and Y) form a ring, with a pair of very small and negatively heteropycnotic m-chromosomes in its centre 6MI from the equator.The homologous autosomes can be seen lying parallel 7 late MI and AI plates. Scale bar = 10 µm.
The behaviour of chromosomes during the first spermatocyte division was quite similar to that in C. rogenhoferi. Unfortunately, we found no second division stages in the two males explored here. When condensing from the diffuse stage (Figs
The chromosome formula of C. coleoptrata was determined as 2n = 24 (20A+2m+XY).
The main goal of this paper was to address the cytogenetic features of two species of Cymatia and compare them with those encountered within the superfamily Corixoidea. This entailed at least four related issues, namely: 1) whether the karyotypes are conservative in respect to chromosome number and sex chromosome system, 2) whether m-chromosomes are present, 3) whether the post-reduction of sex chromosomes is present, and 4) whether the chiasmata are formed in male meiosis. Both Corixidae and Micronectidae are known to be characterised by an XY sex chromosome system and an inverted sequence of X and Y chromosome divisions in spermatocyte meiosis, i.e. the sex chromosome post-reduction (for references see
In Corixinae, each of 30 species studied display ten pairs of autosomes, a pair of very small m-chromosomes, and X and Y chromosomes: the karyotype formula of these species can be expressed as 2n = 24 (20A+2m+X+Y). Meiosis is of a standard chiasmate type in males (
The first (reductional in the majority of organisms) division involves several meiosis-specific events the most important being the formation of chiasmata, the points of genetic crossing-over, between homologous chromosomes. When meiosis is achiasmate and chiasmata are not formed, no diplotene or diakinesis stages can be recognised. The existence of achiasmate meiosis in phylogenetically unrelated true bug families, i.e. Micronectidae from the infraorder Nepomorpha (
The Cymatiainae were erected for the first time as a separate taxon (as Cymatiini) in Corixidae on the basis of the shape and hairiness of the pala, the chitinisation of the pharynx, the length of maxillary stylets, and their position against pharynx (Walton in
Key diagnostic characters used to distinguish Cymatiainae from the rest of Corixidae
Cymatiainae | Corixidae |
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Labium without transverse sulcations | Labium with transverse sulcations |
Absence of transverse pattern of distribution of the labial sensilla | Transverse pattern of distribution of the labial sensilla |
Nodal furrow absent | Nodal furrow present |
Pala elongate, nearly cylindrical in both sexes | Female pala spoon-shaped; male pala variable |
Pala without pegs | Pala with pegs |
Pala in both sexes without palm | Pala in both sexes with palm |
Claw of hind leg inserted apically | Claw of hind leg inserted subapically |
Absence of seta close to the claw’ basis | Presence of seta close to the claw’ basis |
Strigil absent | Usually with strigil |
Unable to stridulate | Stridulation by rubbing peg fields on the anterior femur against the side of the head, females of some species also able to stridulate |
Achiasmate male meiosis | Chiasmate male meiosis |
In different phylogenetic studies on Corixoidea (
This study was financially supported by the grant from the Russian Science Foundation no. 14-14-00541 to the Zoological Institute of Russian Academy of Sciences (for VK) and by the grant OPOS 20-UPRR/17.04.2014 with RIOSW-Russe (for DS). We want to thank Fedor Konstantinov (St. Petersburg University, St. Petersburg), Borislava Gyosheva and Mila Ihtimanska (IBER-BAS, Sofia) for the valuable help in collecting the specimens. We are greatly indebted to Yuri Popov (Borissiak Paleontological Institute, Moscow), Seppo Nokkala (University of Turku, Turku), Pavel Štys (Charles University, Prague), Nico Nieser (Naturalis Biodiversity Centre, Leiden) for reviews and valuable comments and remarks.