An updated Atlas of Helophorus chromosomes

An account is given of my development of techniques to obtain well-spread Giemsa-stained banded chromosome preparations. Apparent G-banding could be obtained following very slight trypsin treatment of freshly prepared slides, but this banding was very fine (close-grained) and possibly not a reflection of chromosome structure. However, treatment of developing embryos in vitro with 5-fluorouridine produced a similar chromomere banding, which is therefore regarded as genuine. Steady accumulation of Helophorus Fabricius, 1775 karyotypes has resulted in the production of an Atlas covering 62 of the 170 species known to occur in the Palaearctic. Chromosome polymorphisms involving pericentric inversions and addition of extra C-banding regions have been found, as well as small B-chromosomes in a few species. In general, karyotypes have proved very useful in establishing the limits of individual species. Parthenogenesis involving triploidy has been found in two species. Karyotypes of experimentally produced hybrids have revealed irregularities in chromosome condensation.

Karyotypes of water scavenger beetles (Coleoptera: Hydrophilidae): new data and review of published records

This study summarizes available data on karyotypes of water scavenger beetles (Coleoptera: Hydrophiloidea: Hydrophilidae), based on newly acquired data of 23 genera and 64 species. We combine these data with previously published data, which we review. In total, karyotypes are available for 33 genera and 95 species, covering all subfamilies and tribes. Available data indicate that most groups of the Hydrophilidae are diploid and sexually reproducing, with XY (♂) and XX (♀) sex chromosomes; the Y chromosome is always minute and does not recombine with X during meiosis. Exceptions are known in Anacaena, with parthenogenetic diploid or triploid populations in some species and sex chromosomes fused with autosomes in others. The diploid number of chromosomes is 2n = 18 in the subfamilies Acidocerinae, Chaetarthriinae, Enochrinae and Hydrophilinae. Variations are known in species of Anacaena and Berosus (both usually with 2n = 18) and in Hydrochara and Hydrophilus with an increased number of chromosomes (2n = 30). The number of chromosomes is increased in the subfamily Cylominae (2n = 24–30) and in all subclades of the subfamily Sphaeridiinae (2n = 22–32). We summarize protocols for obtaining chromosome slides used for this study and provide step-by-step guidelines to facilitate future cytogenetic studies.

A re-examination of the West European species of Boreonectes Angus, 2010, with particular reference to B. multilineatus (Falkenström, 1922) (Coleoptera, Dytiscidae)

The West European species of Boreonectes Angus, 2010 are reviewed. B. multilineatus (Falkenström, 1922) is shown to be widely distributed in the Pyrenees, where it is the only species known to occur. The chromosomes of all five west European species are found to have, in addition their different numbers of chromosomes, differences in the number and locations of secondary constrictions, and in some cases, the number of chromosomes with clear centromeric C-bands. The level of differences between the chromosomes of the species is in stark contrast with the very slight genetic (DNA) differences between them and this suggests that chromosome differentiation may have been a driver of speciation. Two of the species, B. griseostriatus (De Geer, 1774) and B. multilineatus, have distributions extending northwards as far as Arctic Scandinavia. It is pointed out that, while these northern areas now constitute the major portions of their ranges, they must be of fairly recent origins as most of the area would have been covered by ice sheets and therefore not habitable during the glacial maximum of the Last Glaciation. This contrasts with the situation in the area of the Central European mountains where fossil faunas, including Boreonectes, are known. B. griseostriatus, identifiable to species by its parameres, was present in the Woolly Rhinoceros site at Starunia in the Western Ukraine, and this fauna is discussed as well as an English fauna of similar age.

Triploidy in Chinese parthenogenetic Helophorus orientalis Motschulsky, 1860, further data on parthenogenetic H. brevipalpis Bedel, 1881 and a brief discussion of parthenogenesis in Hydrophiloidea (Coleoptera)

The chromosomes of triploid parthenogenetic Helophorus orientalis Motschulsky, 1860 are described from material from two localities in Heilongjiang, China. 3n = 33. All the chromosomes have clear centromeric C-bands, and in the longest chromosome one replicate appears to be consistently longer than the other two. The chromosomes of additional triploid parthenogenetic H. brevipalpis Bedel, 1881, from Spain and Italy, are described. In one Italian population one of the autosomes is represented by only two replicates and another appears more evenly metacentric than in material from Spain and the other Italian locality. Parthenogenetic and bisexual specimens of H. orientalis are illustrated, along with Pleistocene fossil material. Parthenogenetic H. brevipalpis is also illustrated. Parthenogenesis in Hydrophiloidea is discussed. It appears to be rare and, in all cases has been detected by chromosomal analysis of populations in which males are unexpectedly scarce. Parthenogenesis is suspected in Helophorus aquila Angus et al., 2014, from northern Qinghai (China), which should be verified in further studies.

A remarkable new Helophorus species (Coleoptera, Helophoridae) from the Tibetan Plateau (China, Sichuan)

Helophorus dracomontanussp. n. is described from the Tibetan Plateau near Kangding, Sichuan, China. It is a member of the subgenus Helophorus s. str. but the anterolateral part of the pronotum resembles subgenus Gephelophorus Sharp, 1915. The short metallic-black maxillary palpi with almost symmetrical apical segments are suggestive of subgenus Kyphohelophorus Kuwert, 1886, but the elytral flanks are narrower than the epipleurs, excluding the species from that subgenus. An adjusted key to Helophorus s. str. is given to identify the new species, as well as H. jaechi Angus, 1995 and H. kozlovi Zaitsev, 1908.

A chromosomal analysis of Nepa cinerea Linnaeus, 1758 and Ranatra linearis (Linnaeus, 1758) (Heteroptera, Nepidae)

An account is given of the karyotypes and male meiosis of the Water Scorpion Nepa cinerea Linnaeus, 1758 and the Water Stick Insect Ranatra linearis (Linnaeus, 1758) (Heteroptera, Nepomorpha, Nepidae). A number of different approaches and techniques were tried: the employment of both male and female gonads and mid-guts as the sources of chromosomes, squash and air-drying methods for chromosome preparations, C-banding and fluorescence in situ hybridization (FISH) for chromosome study. We found that N. cinerea had a karyotype comprising 14 pairs of autosomes and a multiple sex chromosome system, which is X₁X₂X₃X₄Y (♂) / X₁X₁X₂X₂X₃X₃X₄X₄ (♀), whereas R. linearis had a karyotype comprising 19 pairs of autosomes and a multiple sex chromosome system X₁X₂X₃X₄Y (♂) / X₁X₁X₂X₂X₃X₃X₄X₄ (♀). In both N. cinerea and R. linearis, the autosomes formed chiasmate bivalents in spermatogenesis, and the sex chromosome univalents divided during the first meiotic division and segregated during the second one suggesting thus a post-reductional type of behaviour. These results confirm and amplify those of Steopoe (1925, 1927, 1931, 1932) but are inconsistent with those of other researchers. C-banding appeared helpful in pairing up the autosomes for karyotype assembly; however in R. linearis the chromosomes were much more uniform in size and general appearance than in N. cinerea. FISH for 18S ribosomal DNA (major rDNA) revealed hybridization signals on two of the five sex chromosomes in N. cinerea. In R. linearis, rDNA location was less obvious than in N. cinerea; however it is suggested to be similar. We have detected the presence of the canonical "insect" (TTAGG) _n telomeric repeat in chromosomes of these species. This is the first application of C-banding and FISH in the family Nepidae.

Further studies on Boreonectes Angus, 2010, with a molecular phylogeny of the Palaearctic species of the genus

Karyotypes are given for Boreonectes emmerichi (Falkenström, 1936) from its type locality at Kangding, China, and for B. alpestris (Dutton & Angus, 2007) from the St Gotthard and San Bernardino passes in the Swiss Alps. A phylogeny based on sequence data from a combination of mitochondrial and nuclear genes recovered western Palaearctic species of Boreonectes as monophyletic with strong support. Boreonectes emmerichi was placed as sister to the north American forms of B. griseostriatus (De Geer, 1774), although with low support. The diversity of Palaearctic species of the B. griseostriatus species group is discussed.

A chromosomal analysis of eleven species of Gyrinidae (Coleoptera)

Karyotypes are presented for 10 species of Gyrinus Geoffroy, 1762: Gyrinus minutus Fabricius, 1798, Gyrinus caspius Ménétriés, 1832, Gyrinus paykulli Ochs, 1927, Gyrinus distinctus Aubé, 1836 var. fairmairei Régimbart, 1883, Gyrinus marinus Gyllenhal, 1808, Gyrinus natator (Linnaeus, 1758), Gyrinus opacus Sahlberg, 1819, Gyrinus substriatus Stephens, 1869, Gyrinus suffriani Scriba, 1855, Gyrinus urinator Illiger, 1807 and for Orectochilus villosus (Müller, 1776) (Coleoptera: Gyrinidae). The 10 Gyrinus species have karyotypes comprising 13 pairs of autosomes plus sex chromosomes which are X0 (♂), XX (♀), with the X chromosomes the longest in the nucleus. Orectochilus villosus has 16 pairs of autosomes plus X0, XX sex chromosomes. The data obtained by Saxod and Tetart (1967) and Tetart and Saxod (1968) for five of the Gyrinus species are compared with our results. Saxod and Tetart considered the X chromosome to be the smallest in the nucleus in all cases, and this is considered to result from confusion arising from uneven condensation of some of the chromosomes. Small differences between the chromosomes of different Gyrinus species have been detected, but not between Greenland and Swedish populations of Gyrinus opacus, nor between typical Gyrinus distinctus from France and Gyrinus distinctus var. fairmairei from Kuwait.

Comparison of different cytogenetic methods and tissue suitability for the study of chromosomes in Cimex lectularius (Heteroptera, Cimicidae)

In the article we summarize the most common recent cytogenetic methods used in analysis of karyotypes in Heteroptera. We seek to show the pros and cons of the spreading method compared with the traditional squashing method. We discuss the suitability of gonad, midgut and embryo tissue in Cimex lectularius Linnaeus, 1758 chromosome research and production of figures of whole mitosis and meiosis, using the spreading method. The hotplate spreading technique has many advantages in comparison with the squashing technique. Chromosomal slides prepared from the testes tissue gave the best results, tissues of eggs and midgut epithelium are not suitable. Metaphase II is the only division phase in which sex chromosomes can be clearly distinguished. Chromosome number determination is easy during metaphase I and metaphase II. Spreading of gonad tissue is a suitable method for the cytogenetic analysis of holokinetic chromosomes of Cimex lectularius.

Further karyosystematic studies of the Boreonectesgriseostriatus (De Geer) group of sibling species (Coleoptera, Dytiscidae)-characterisation of B.emmerichi (Falkenström, 1936) and additional European data

A lectotype is designated for the Tibetan species Deronectesemmerichi Falkenström, 1936 (Currently Boreonectesemmerichi (Falkenström)), and its habitus, as well as the median lobe and parameres of its aedeagus, are figured along with additional comparative material. Material of Boreonectesemmerichi from Sikkim (BMNH) represents the first record of a Boreonectes Angus, 2010 species from India. The karyotype of Boreonectesemmerichi is described as having 26 pairs of autosomes plus sex chromosomes which are X0 (♂), XX (♀). The karyotype is most like that of Boreonectesmacedonicus (Géuorguiev, 1959), but with slight differences. Additional chromosomal information is given for Boreonectesgriseostriatusgriseostriatus (De Geer, 1774) in the French Alps, Boreonectesgriseostriatusstrandi (Brinck, 1943) on the Kola Peninsula, Boreonectesmultilineatus (Falkenström, 1922) in the Pyrenees and Boreonectesibericus (Dutton & Angus, 2007) in the Spanish Picos de Europa.

Further karyosystematic studies of the Boreonectesgriseostriatus (De Geer) group of sibling species (Coleoptera, Dytiscidae)-characterisation of B.emmerichi (Falkenström, 1936) and additional European data

A lectotype is designated for the Tibetan species Deronectesemmerichi Falkenström, 1936 (Currently Boreonectesemmerichi (Falkenström)), and its habitus, as well as the median lobe and parameres of its aedeagus, are figured along with additional comparative material. Material of Boreonectesemmerichi from Sikkim (BMNH) represents the first record of a Boreonectes Angus, 2010 species from India. The karyotype of Boreonectesemmerichi is described as having 26 pairs of autosomes plus sex chromosomes which are X0 (♂), XX (♀). The karyotype is most like that of Boreonectesmacedonicus (Géuorguiev, 1959), but with slight differences. Additional chromosomal information is given for Boreonectesgriseostriatusgriseostriatus (De Geer, 1774) in the French Alps, Boreonectesgriseostriatusstrandi (Brinck, 1943) on the Kola Peninsula, Boreonectesmultilineatus (Falkenström, 1922) in the Pyrenees and Boreonectesibericus (Dutton & Angus, 2007) in the Spanish Picos de Europa.

Karyotypes of some medium-sized Dytiscidae (Agabinae and Colymbetinae) (Coleoptera)

An account is given of the karyotypes of 29 species of medium sized Dytiscidae (Coleoptera). Of the 20 species of Agabus Leach, 1817, 18 have karyotypes comprising 21 pairs of autosomes and sex chromosomes which are either X0(♂) or XX (♀). These species are Agabus serricornis (Paykull, 1799), Agabus labiatus (Brahm, 1791), Agabus congener (Thunberg, 1794), Agabus lapponicus (Thomson, 1867), Agabus thomsoni (J. Sahlberg, 1871), Agabus confinis (Gyllenhal, 1808), Agabus sturmii (Gyllenhal, 1808), Agabus bipustulatus (Linnaeus, 1767), Agabus nevadensis Håkan Lindberg, 1939, Agabus wollastoni Sharp, 1882, Agabus melanarius Aubé, 1837, Agabus biguttatus (Olivier, 1795), Agabus binotatus Aubé, 1837, Agabus affinis (Paykull, 1798), Agabus unguicularis (Thomson, 1867), Agabus ramblae Millan & Ribera, 2001, Agabus conspersus (Marsham, 1802) and Agabus nebulosus (Forster, 1771). However two species, Agabus infuscatus Aubé, 1838 and Agabus adpressus Aubé, 1837, have developed a neo-XY system, with karyotypes comprising 21 pairs of autosomes and XY sex chromosomes (♂). No chromosomal differences have been detected between typical Agabus bipustulatus and Agabus bipustulatus var. solieri Aubé, 1837, nor have any been found between the three species of the Agabus bipustulatus complex (Agabus bipustulatus, Agabus nevadensis and Agabus wollastoni). The four species of Colymbetes Clairville, 1806, Colymbetes fuscus (Linnaeus, 1758), Colymbetes paykulli Erichson, 1837, Colymbetes piceus Klug, 1834 and Colymbetes striatus (Linnaeus, 1758) have karyotypes comprising 20 pairs of autosomes and sex chromosomes which are X0 (♂), XX (♀). Two of the species of Rhantus Dejean, 1833, Rhantus exsoletus (Forster, 1771) and Rhantus suturellus (Harris, 1828) have karyotypes comprising 20 pairs of autosomes and X0/XX sex chromosomes, but the other three species, Rhantus grapii (Gyllenhal, 1808), Rhantus frontalis (Marsham, 1802) and Rhantus suturalis (Macleay, 1825) have 22 pairs of autosomes and X0/XX sex chromosomes. Agabus congener and Rhantus suturellus may have one B-chromosome. Nine of the species have previously published karyotype data but for seven of these the data are wrong and are here corrected.

A chromosomal investigation of some European Leiodidae (Coleoptera), with particular focus on Spanish subterranean Leptodirini

Karyotypes are shown for Leiodes calcarata (Erichson, 1845), Catops coracinus Kellner, 1846, Cantabrogeus luquei (Salgado, 1993), Espanoliella luquei Salgado & Fresneda, 2005, Fresnedaella lucius Salgado, Labrada & Luque, 2011, Notidocharis uhagoni (Sharp 1872), Quaestus (Quaesticulus) pasensis Salgado, Labrada & Luque, 2010, all of which are shown to have a diploid number of 20 autosomes plus Xy (♂) or XX (♀) sex chromosomes, as well as an as yet undescribed triploid species of the genus Cantabrogeus Salgado, 2000. These results are contrasted with published information, all on Leptodirini, which lists 10 species as having diploid numbers of 22 + Xy or XX. It is shown that the higher chromosome number (n = 11 + X or y) previously reported refers exclusively to the more derived Leptodirini ("infraflagellates") whereas the lower number (n = 10 + X or y) refers to the less derived surface-dwelling forms and the less derived Leptodirini ("supraflagellates").

A long-living species of the hydrophiloid beetles: Helophorus sibiricus from the early Miocene deposits of Kartashevo (Siberia, Russia)

The recent hydrophiloid species Helophorus (Gephelophorus) sibiricus (Motschulsky, 1860) is recorded from the early Miocene deposits of Kartashevo assigned to the Ombinsk Formation. A detailed comparison with recent specimens allowed a confident identification of the fossil specimen, which is therefore the oldest record of a recent species for the Hydrophiloidea. The paleodistribution as well as recent distribution of the species is summarized, and the relevance of the fossil is discussed. In addition, the complex geological settings of the Kartashevo area are briefly summarized.

A chromosomal investigation of some British Cantharidae (Coleoptera)

The karyotypes of 20 species of Cantharidae occurring in the British Isles are described and illustrated, 19 of which are hitherto unrecorded. These are Cantharis cryptica Ashe, Cantharis fusca Linnaeus, Cantharis lateralis Linnaeus, Cantharis livida Linnaeus, Cantharis nigra (Degeer), Cantharis nigricans (O. F. Müller), Cantharis pallida Goeze, Cantharis pellucida Fabricius, Cantharis rufa Linnaeus, Cantharis rustica Fallén, Cantharis thoracica (Olivier), Rhagonycha fulva (Scopoli), Rhagonycha lignosa (O. F. Müller), Rhagonycha limbata Thomson, Rhagonycha lutea (O. F. Müller), Rhagonycha testacea (Linnaeus), Silis ruficollis (Fabricius), Malthinus seriepunctatus Kiesenwetter, Malthodes dispar (Germar) and Malthodes minimus (Linnaeus). The main findings were as follows: (1) Cantharis, Rhagonycha and Silis have karyotypes of six pairs of autosomes plus sex chromosomes, which are X0 (male), XX (female). (2) Malthinus and Malthodes differ from the other genera in having only five pairs of autosomes. (3) The chromosome complement of Silis differs from those of the other genera studied in having a variable number of B-chromosomes in individuals from the same population. (4) The karyotypes of the Rhagonycha species show a degree of uniformity in the relative chromosome lengths, centromere positions and C-banding patterns. (5) The karyotypes of the Cantharis species are much more distinct from each other where these characteristics are concerned. (6) Maturation of the gonads takes place in the late larval stage. (7) The segregation of the X chromosome of Cantharis rufa during meiosis is pre-reductional.

A chromosomal investigation of some European species of Haliplidae (Coleoptera)

The karyotypes of 15 European species of Haliplidae are described and illustrated. The sex chromosomes are X0 in <em>Brychius elevatus </em>and Peltodytes caesus, and XY in 13 species of <em>Haliplus</em>. The number of autosome pairs is 16 in <em>Peltodytes caesus</em>, 19 in <em>Brychius elevatus</em>, 17 in <em>Haliplus (Liaphlus) fulvus,</em> 15 in H. <em>(L.) variegatus</em>, 14 in H. <em>(L.) flavicollis</em>, 11 in <em>H. (L.) laminatus</em>, 9 in <em>H. (L.) mucronatus</em>, and 11 in <em>H. (Haliplidius)</em> obliquus and <em>H. (H.) confinis</em>, <em>H. (Neohaliplus) lineatocollis</em> and five species of <em>H. (Haliplus).</em> It is suggested that the X0 sex chromosome system, the most common in the Adephaga, is plesiotypic for Haliplidae, and that the XY systems are a synapomorphy of the family, and are neo-XY in origin. There is no good evidence of Xyp systems of the type found in Polyphaga. The diversity of karyotypes shown by species of the subgenus <em>Liaphlus</em> is contrasted with the near uniformity shown by other groups. Interspecific differences between karyotypes are noted.

A chromosomal investigation of the west European species of Corixa Geoffroy (Heteroptera: Corixidae)

C-banded karyotypes are provided for the five west European species of Corixa Geoffroy. All have 2n = 22 autosomes + sex chromosomes which are XY (male symbol), XX (female symbol). Some specimens of C. punctata have a small B-chromosome, while some C. panzeri have a fairly large one. The karyotypes of C. punctata, C. dentipes, C. affinis and C. panzeri are all distinctive, but the karyotypes of C. punctata and C. iberica appear indistinguishable. The Scottish material of C. punctata and C. iberica used in this study shows morphological intergradation between the two, suggesting that they hybridise where their ranges overlap. Meiosis shows very fine even pachytene bands in C. punctata, and that the autosomes form true bivalents during diplotene in C. affinis and C. panzeri, while the sex chromosomes appear closely associated. At first metaphase the sex chromosomes may appear either closely associated or may have separated. There is no evidence of the presence of m-chromosomes.

A chromosomal analysis of some water beetle species recently transferred from Agabus Leach to Ilybius Erichson, with particular reference to the variation in chromosome number shown by I. montanus Stephens (Coleoptera: Dytiscidae)

The karyotypes of seven Ilybius species are described and illustrated. All except I. wasastjernae have a basic karyotype of 34 autosomes plus sex chromosomes which are X0 (♂), XX (♀), with the X chromosome among the largest in the nucleus. This karyotype appears to be the norm for Ilybius and supports the transfer of the species concerned from Agabus to Ilybius. I. wasastjernae has 36 autosomes and the X chromosome is the smallest in the nucleus and its karyotype is unlike any other known karyotype in either Ilybius or Agabus. In most of the species studied no intraspecific variation has been detected. Exceptions are I. chalconatus, where there is one inversion polymorphism in one of the autosomes, and I. montanus whose autosome number has been found to vary from 29 to 34. Such variation is highly unusual among Coleoptera. The variation results from fusion‐fission polymorphisms involving three different pairs of autosomes. In each case the fusions may be homozygous, heterozygous or absent. All populations investigated were polymorphic for some of the fusions, but only one (La Salceda, Spain) included individuals lacking all fusions. The frequencies of fused and unfused chromosomes were analysed in three English populations. In only one case was there a departure from the values expected from the Hardy‐Weinberg equilibrium, and this population also showed a significant difference from the other two. Meiosis in males heterozygous for fusions involves the production of trivalents in first division, but results in the production of abundant sperm, with no evidence of chromosomal abnormalities in second metaphase, or of degenerating cells as a result of failed meiosis. The three fusions sites are consistent in all the populations studied, and it is concluded that these fusions represent unique historical events rather than current chromosomal instability.

The C-banded karyotypes of the four British species of Notonecta L. (Heteroptera: Notonectidae)

Chromosome preparations were made from mid-gut and ovarian cells of adult Notonecta glauca L., N. obliqua Thunberg, N. maculata F. and N. viridis Delcourt, using the acetic acid dissociation, air-drying method (Crozier 1968) with Giemsa staining. C-banding was obtained by treatment with barium hydroxide and salt-sodium citrate (2xSSC). The karyotypes of the first three species are very similar, with 11 pairs of autosomes plus XY sex chromosomes (plus sometimes a small 12th autosome pair in N. glauca), and the sequence of chromosome sizes very similar. However, the four longest pairs of autosomes, and the X chromosomes, have characteristic C-band patterns, which differ between the species. The karyotype of N. viridis is more distinct, with one pair of long autosomes, while the remaining chromosomes are much shorter. The long autosomes have distinct C-bands, but these are present in only one of the shorter pairs, as faint terminal bands. In warm conditions the long autosomes of N. viridis appear rod-like, but in cold conditions they have one end heavily condensed, giving a tadpole-like appearance.

The C-banded karyotypes of the four British species of Notonecta L. (Heteroptera: Notonectidae)

Chromosome preparations were made from mid-gut and ovarian cells of adult Notonecta glauca L., N. obliqua Thunberg, N. maculata F. and N. viridis Delcourt, using the acetic acid dissociation, air-drying method (Crozier 1968) with Giemsa staining. C-banding was obtained by treatment with barium hydroxide and salt-sodium citrate (2xSSC). The karyotypes of the first three species are very similar, with 11 pairs of autosomes plus XY sex chromosomes (plus sometimes a small 12th autosome pair in N. glauca), and the sequence of chromosome sizes very similar. However, the four longest pairs of autosomes, and the X chromosomes, have characteristic C-band patterns, which differ between the species. The karyotype of N. viridis is more distinct, with one pair of long autosomes, while the remaining chromosomes are much shorter. The long autosomes have distinct C-bands, but these are present in only one of the shorter pairs, as faint terminal bands. In warm conditions the long autosomes of N. viridis appear rod-like, but in cold conditions they have one end heavily condensed, giving a tadpole-like appearance.