Research Article |
Corresponding author: Robert B. Angus ( r.angus@rhul.ac.uk ) Academic editor: Snejana Grozeva
© 2021 Robert B. Angus.
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:
Angus RB (2021) A re-examination of the West European species of Boreonectes Angus, 2010, with particular reference to B. multilineatus (Falkenström, 1922) (Coleoptera, Dytiscidae). Comparative Cytogenetics 15(1): 23-39. https://doi.org/10.3897/compcytogen.v15.i1.60188
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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.
Boreonectes, B. multilineatus, chromosomes, Coleoptera, Distributions, Dytiscidae, Pyrenees, Pleistocene fossils
For Ignacio Ribera, 1963–2020. Taken from us by the Corona virus when he still had so much research to enjoy and to share with the rest of us.
Boreonectes
Angus, 2010 is a genus of small diving beetles (Dytiscidae) typically found in mountain lakes and in barren pools at lower altitudes in the north. The Palaearctic species were for many years regarded as all belonging to a single species, B. griseostriatus (De Geer, 1774) (see
No | Species | Distribution |
1 | Boreonectes griseostriatus (De Geer, 1774) | Fennoscandia, Alps (northern) |
= B. maritimus (Helliesen, 1890) | ||
= B. griseostriatus var. nigrescens Favre, 1890 | ||
1a | B. griseostriatus griseostriatus (De Geer, 1774) | |
1b | B. griseostriatus strandi (Brink, 1943) | Arctic coast of Fennoscandia and Kola |
2 | Boreonectes multilineatus (Falkenström, 1922) | Pyrenees, Inland Scandinavia, British Isles, Faroes |
3 | Boreonectes emmerichi (Falkenström, 1936) | Tibetan Plateau |
4 | Boreonectes macedonicus (Guéorguiev, 1959) | North Macedonia, Crete |
= B. creticus (Dutton et Angus, 2007) | ||
5 | Boreonectes alpestris (Dutton et Angus, 2007) | Alps (southern) |
6 | Boreonectes ibericus (Dutton et Angus, 2007) | Mountains of Iberia, Maritime Alps, Corsica, Middle Atlas Mts |
7 | Boreonectes inexpectatus (Dutton et Angus, 2007) | France, Hautes Alpes, Lac du Lauzet inférieur |
8 | Boreonectes riberae (Dutton et Angus, 2007) | Bulgaria, Turkey (Anatolia) |
9* | Boreonectes piochardi (Régimbart, 1878) | Israel/Lebanon, Mt Hermon |
10* | Boreonectes palaestinus (Baudi di Selve, 1894) | Palestine, Syria |
B. multilineatus
(Falkenström, 1922) is among these chromosomally validated species, and was taken to refer to paler, more distinctly striped material from inland montane areas in Fennoscandia, with B. griseostriatus occurring in coastal rocky localities (
In view of these discoveries the known distribution of B. multilineatus is reviewed and a detailed chromosomal comparison of all five West European Boreonectes is undertaken.
The B. multilineatus used in this study is listed in Table
The methods used for preparing chromosomes and the handling of the data are those used by
Localities of the B. multilineatus material used for chromosome analysis.
Country | Locality, date & collector | Coordinates | Number examined + reference |
---|---|---|---|
SWEDEN | Västerbotten, Åmsele, viii.1990, A.N. Nilsson | 64.528°N, 19.350°E | 3 ♂♂. |
SCOTLAND | Kirkcudbright, Clatteringshaws Loch, viii.1990, G. N. Foster | 55.067°N, 4.282°W | 4♂♂, 1♀. |
FRANCE | Lac d’Oncet, 11.ix.2010, F. Bameul. | 42.927°N, 0.1335°E | 2♂♂, 3♀♀. |
Lac d’Anapéou, 30.vii.2011, F. Bameul. | 42.926°N, 0.1284°W | 5♂♂. |
|
Etangs de Fontargente, 5.ix.2015, F. Bameul. | 42.630°N, 1.710°E | 1♂, 1♀. This paper | |
SPAIN | Ibón de las Isérias, 18.vii.2015, F. Bameul. | 42.745°N, 0.479°W | 3♂♂, 1♀. This paper |
Ibón de Anayet Este, 12.viii.2017, F. Bameul. | 42.780°N, 0.4405°W | 2♂♂. This paper | |
Bielsa, “Ibón de Urdicito 1”, 29.viii.2015, F. Bameul. | 42.669°N, 0.278°E | 1♂, 2♀♀. This paper | |
Chistén, “Ibón de Urdicito 2” Ibones de la Solana de Urdicito, 29.viii.2015, F. Bameul. | 42.666°N, 0.286°E | ||
Northern IRELAND | Antrim, Garron Plateau above Glen Arrif, R. Anderson, 3.vi.2008 | 55.003°N, 6.062°W | 4♀♀. Angus, 2008 |
IRELAND | Cork, NW Bonane, small lake 451 m a.s.l. on Glenlough Mountain K. Scheers, J. Bergsten & A. N. Nilsson, 10.vi.2018 | 51.746°N, 9.644°W | 1 ♂, 2♀♀. This paper. |
The Pyrenean distribution of B. multilineatus is shown in Fig.
Mitotic chromosomes, arranged as karyotypes, are shown in Fig.
Map showing the Pyrenean localities for B. multilineatus. For details of the localities see Table
Map showing the Irish localities from which B. multilineatus chromosomes have been obtained.
B. multilineatus and griseostriatus, habitus a, b multilineatus, Ireland, county Cork a ♀ b ♂ c B. griseostriatus, Switzerland, Le Louché d B. griseostriatus var nigrescens Favre, Switzerland, Le Louché. Scale bar: 1 mm for (a, b); c, d are field photographs by Dr E. M. Angus.
B. multilineatus
– mitotic chromosomes from midgut and testis (a–o), metaphase I of meiosis, from testis (p–r) a ♂, Sweden, Åmsele, plain (Giemsa stained), shown as fig. 2o by
Karyotypes for comparison of the West European species are shown in Figs
Centromere positions from Centromere Indices (CI), the length of the shorter chromosome as a percentage of the total length of the chromosome, based on
Chromosome | B. griseostriatus | B. multilineatus | B. alpestris | B. inexpectatus | B. ibericus |
---|---|---|---|---|---|
1 | sm | m | m - sm | -C sm | - C m (+ 24), sm (alone) |
2 | 2c | 2c | 2c | m | m |
3 | sm - m | m - sm | m | sa | sm |
4 | m | m | m | sa | -C 2c |
5 | 2c | 2c | 2c | m | -C sm |
6 | sm | 2c | sm | sm | m |
7 | sm - m | m | m | m | 2c |
8 | 2c | 2c | sm | 2c | -C m |
9 | m | m | m - sm | Sa | m (C very weak) |
10 | m | m | m | 2c | -C m |
11 | m | 2c | sm - sa | m | -C m |
12 | 2c | sm - sa | sm - sa | sa | Sm |
13 | sa | m | m | sm | 2c |
14 | m | m | m | sm | -C m |
15 | sm - sa | m | m | m | 2c (C very weak) |
16 | m | 2c | m | m | -C m |
17 | m | sa | sm | sm | -C m |
18 | m | sa | sm | m | -C sm |
19 | m | m - sm | m - sm | m | -C sm/sa |
20 | m - sm | m | m | m | -C sm |
21 | m - sm | m | m | sa | m (C sometimes weak) |
22 | m - sm | m | m | -C m | -C m |
23 | sm - sa | m | m | m | -C sm |
24 | sa | m | m - sm | sm | -C sa/sm |
25 | m | m | m | m | Sm |
26 | m | m | m - sm | m | -C sm |
27 | m | m | m | sm | – |
28 | sm (northern) m (Alpine) | m - sm (dot) | – | 2c | – |
29 | sm (northern) m (Alpine) | – | – | m | – |
30 | sm (dot) | – | – | – | – |
X | m | m | m | m | sm |
B. griseostriatus
has the highest number of chromosomes of any of the species considered here, with 30 pairs of autosomes and X0/XX sex chromosomes. The metric data are: Measured lengths of autosome 1 2.53–1.99 µ, of autosome 29 1.73–0.87 µ, of autosome 30 (often dot-like) 1.28–0.71 µ. The values for the X chromosome are 4.42–2.3 µ. The RCLs of the autosomes range from about 4 (autosome 1) to about 2 (autosome 29) and about 1.6 (autosome 30). The RCL of the X chromosome is about 6.5. Other features of the chromosomes are given in Table
Boreonectes griseostriatus
(a–m) and B. multilineatus (n–r) at higher magnification, for detailed comparison. a–e northern localities a ♂, Sweden, Öregrund (shown as fig. 2a by
B. multilineatus
has six clear secondary constrictions on autosomes 2, 5, 6, 8, 11 and 16, shown on the C-banded preparation in Fig.
B. alpestris
has a karyotype at first sight closely resembling that of B. multilineatus but has only 27 pairs of autosomes plus the usual X0 or XX sex chromosomes. The metric data are: measured lengths of autosome 1 3.75–2.68 µ, of autosome 26 2.25–2.02 µ, of autosome 27 1.97–1.66 µ and of the X chromosome 6.25–3.3 µ. The RCLs range from about 4 (autosome 1) to about 2.15 (autosome 26) and about 1.8 (autosome 27), while that of the X chromosome ranges from about 8.35–5.79. Other features are given in Table
B. griseostriatus
(a), B. inexpectatus (b, c), B. multilineatus (d) and B. alpestris (e–j) at higher magnification, for detailed comparison a B. griseostriatus, ♂, C-banded, Petit St Bernard (as fig. 2m) c, d B. inexpectatus, paratypes b plain (Giemsa stained) c C-banded c is the nucleus shown as fig. 2i by
B. inexpectatus
has a karyotype comprising 29 pairs of autosomes and X0, XX sex chromosomes, and thus, in terms of numbers of chromosomes, is the species coming closest to B. griseostriatus. The metric data are: measured lengths of autosome 1 2.8–2.4 µ, of autosome 28 1.16–1.06 µ, of autosome 29 0.75–0.63 µ and of the X chromosome 4.16–3.12 µ. The RCLs range from about 5.9 (autosome 1) to about 2.25 (autosome 28) and about 1.4 (autosome 29), while that of the X chromosome is about 7. Other features are given in Table
B. ibericus has the most distinctive karyotype of any of the West European species. It has 24–26 pairs of autosomes, with a fusion-fission polymorphism involving pairs 1 and 24. The sex chromosomes are X0 (♂), XX (♀), with the X chromosome clearly submetacentric, as against metacentric in all the other species. 15 pairs of autosomes lack centromeric C-bands, 1 pair (No. 8) may be with or without C-bands, and 3 pairs have them very weak. The metric data are: measured lengths of autosome 1 5.62–2.8 µ (fused with autosome 24), 3.93–2.5 µ (unfused), of autosome 24 1.25–1 µ, of autosome 26 1.45–0.62 µ and of the X chromosome 6.66–3.12 µ. Secondary constrictions are present on autosome pairs 4, 7, 13 and 15.
B. ibericus
at higher magnification, for detailed comparison (a–k) a–c paratypes, Spain, Peña Lara, plain (Giemsa stained) a ♂, autosomes 1 and 24 homozygous fused b ♂, autosomes 1 and 24 heterozygous for fusion c ♀, autosomes 1 and 24 homozygous unfused; shown as fig. 2j–l by
The West European species of Boreonectes show a striking diversity of karyotypes, in sharp contrast to their genetic (DNA) differences which are very slight (
There is some fossil evidence for these beetles in central Europe during the Last Glaciation. Boreonectes is among the beetles at the famous Woolly Rhinoceros site at Starunia near Lvov in the western Ukraine (
I thank all who have sent me living Boreonectes over the years: Anders Nilsson, Bo Svenson, Garth Foster, Lars Hendrich, Johannes Bergsten, Kevin Scheers and especially Franck Bameul whose heroic efforts in the Pyrenees revealed not only the completely unexpected presence of B. multilineatus but also its extensive range there. I thank my daughter Lizzie (Dr E.M. Angus) for her help in the field and for her photographs of Alpine B. griseostriatus var. nigrescens, and Hans Fery for showing me the type of Hydroporus piochardi Régimbart. I thank the Natural History Museum, London for the use of its facilities and my continuing position as a Scientific Associate in the Department of Life Sciences (Insects) and the School of Biological Sciences, Royal Holloway University of London for facilities to develop and print chromosome films. I thank the two reviewers of this paper, Prof. G. N. Foster and Prof. B. Dutrillaux for their very helpful suggestions, as well as the subject editor, Dr. S. Grozeva, for her careful scrutiny of the manuscript.