A third karyosystematic investigation of the Stictotarsus griseostriatus ( De Geer ) group of sibling species ( Coleoptera : Dytiscidae )

Karyological analysis has been carried out on Stictotarsus griseostriatus (De Geer, 1774) from Tjøme in southern Norway, one of the type localities of Deronectes maritimus Helliesen, 1890, as well as from the Canton of Valais in the Swiss Alps and Bavaria in the German Alps. True S. griseostriatus is shown to occur over much of the central Alps, and the synonymy of S. griseostriatus var. nigrescens Favre, 1890 is confi rmed. Analysis of Corsican material shows that the species inhabiting the island is S. ibericus Dutton et Angus, 2007. The known distributions of the S. griseostriatus group species occurring in the Alps and on Corsica are given, and Pleistocene fossil material from Starunia in the Ukrainian Carpathians is fi gured and discussed. A syntype of Potamodytes multilineatus Falkenström, 1922, in Helliesen’s collection in Oslo, is noted and a neotype designated for Deronectes maritimus Helliesen, 1890 as the original material on which the description was based cannot be found.


INTRODUCTION
The Stictotarsus griseostriatus group of sibling species was shown by Dutton and Angus (Dutton, Angus, 2007) to comprise seven species in Europe, effectively indistinguishable from one another morphologically, but with distinct karyotypes and clearly different distributions.In a subsequent publication Angus (2008) synonymised S. creticus Dutton et Angus, 2007with S. macedonicus (Georgiev, 1959), and showed that S. griseostriatus strandi (Brinck, 1943) is chromosomally identical with nominative subspecies S. griseostriatus, and that S. griseostriatus, in a distinctly striped form reminiscent of S. multilineatus (Falken-ström, 1922), occurs in Finnish Lapland.Angus further noted that since these Finnish S. griseostriatus had a facies resembling S. multilineatus, presumably habitat-determined, it seemed possible that coastal Deronectes maritimus Helliesen, 1890 (S. maritimus), might perhaps be a habitat-determined form of S. multilineatus.Angus further noted that Hydroporus griseostriatus var.nigrescens Favre, 1890 (S. griseostriatus var. nigrescens), from the Alps of Chandolin (Valais, Switzerland) seems to be an unknown species as S. griseostriatus itself did not occur in the Alps.The primary objectives of the present study were to establish the identities of S. maritimus and R.B. Angus Comp. Cytogenet., 2010 4(1) Comparative Cytogenetics S. griseostriatus var.nigrescens, and to fi nd out which species occurs on the high mountains of Corsica.

MATERIAL AND METHODS
The material used for chromosome analysis is listed in Table 1, and the localities are shown on the maps in Figs 1 and 2. The methods are as described by Dutton, Angus (2007) and unless otherwise stated the material is in the author's collection in the Natural History Museum, London.The Starunia fossil material is on loan from the Zoological Museum, Krakow.

RESULTS
Mitotic chromosomes, arranged as karyotypes, are shown in Fig. 3.
A plain male karyotype from Tjøme, Norway, is shown as Fig. 3, c.This karyotype shows no difference from those of the Swedish material, and confi rms that Deronectes maritimus Helliesen, 1890, described from coastal rock pools on Tjøme and neighbouring localities, is indeed true S. griseostriatus.
Alpine material is shown in Fig. 3, d-g.Again, these karyotypes show no taxonomically important differences from those of the Swedish material, showing that true S. griseostriatus does occur in the Alps, contrary to Dutton, Angus (2007) and Angus (2008).The Swiss material (Fig. 3, d, e) is from two localities by Le Louché, just west of the hydroelectric Lac de Moiry in the canton of Valais.This locality is only about 12 km S of the Alpes de Chandolin by Mt Bella Tola, just the other side of the Val d'Anniviers, from where Favre (1890) described his Hydroporus griseostriatus var.nigrescens.This was described as having the elytra almost black (Elytres presque noires).In the lower of the Le Louché localities, a lake with a dark bottom with sparse submerged vegetation, some of the specimens, including the one whose karyotype is fi gured, had almost totally black elytra.This specimen may therefore be taken as confi rming the identity of Hydroporus griseostriatus var.nigrescens as a form of S. griseostriatus (De Geer).The material in the higher of the Le Louché localities, a small silty pool, is all of the distinctly striped form, with the ground colour dull yellowish.First metaphase of shows the unpaired X chromosome, confi rming the interpretation given by Angus ( 2008), using Finnish material.Fig. 3, f, g shows the karyotype of a Bavarian male.This karyotype identifi es the material as S. griseostriatus, indicating that this species is widely distributed over the main part of the Alps.

S. ibericus Dutton et Angus, 2007
Karyotypes of Spanish and French paratypes are shown in Fig. 3, h, i.A karyotype of a Corsican male is shown in Fig. 3, j (plain) and k (C-banded).There is no taxonomically signifi cant difference between these karyotypes.S. ibericus is characterised by a fusion-fi ssion polymorphism involving autosomes 1 and 24, by the X chromosome not being the longest in the nucleus (as in other known karyotypes from the S. griseostriatus group), and by the small number of autosomes (5 pairs) with distinct centromeric C-bands.The Corsican material is referable to S. ibericus on all these characters (the material fi gured is all heterozygous for the fusion-fi ssion polymorphism) and shows no other feature to distinguish it from S. ibericus.

Pleistocene fossil material
The identifi cation of S. griseostriatus in the Alps shows it to be a true glacial relict.Fossils of S. griseostriatus group species are not uncommon in sites referable to colder episodes of the Last (Weichselian or Devensian) Glaciation in Britain, but more relevant to Alpine distributions is their occurrence in the mid-Weichselian deposits at Starunia near Lviv in the western Ukraine.This site, famous for the exceptional preservation of its insect remains because of a mixture of oil and salt (sodium chloride), was fi rst described by Łomnicki (1914a).The initial interest in this site stemmed from the discovery of the mummifi ed remains of a Woolly Rhinoceros, but the insect remains described by Łomnicki (1914b) were anomalous, all representing species living in that area at the present time.The matter was resolved by an expedition from the University of Krakow in 1929, leading to the discovery of a second Woolly Rhinoceros (Nowak, Panow, 1930) and the fi nding that the original insects were contaminants from surface material buried in the original shaft.The insects from this second site are a true Pleistocene assemblage, and have been radiocarbon dated to 23 255 ± 775 years B.P (SI-642).Angus (1973) gave an account of the Helophorus species (Helophoridae), and Zeuner (1934) described the Orthoptera.S. griseostriatus sensu lato is present among the unreported Norway, Vestfold, Tjøme (Fig. 1) 6 ♂, 5 ♀ Switzerland, Valais, Le Louché (Fig. 2) 8 ♂, 1 ♀ Germany, Bavaria, Seeon Alm (Fig. 2

DISCUSSION
The confi rmation that material from southern Norwegian rock pools is true S. griseostriatus rather than a form of S. multilineatus (Falkenström, 1922), as seemed possible in view of the variation in appearance now known in S. griseostriatus (Angus, 2008), removes any lingering uncertainty over the identity of the Scandinavian forms.The situation may now be stabilised by reference to type material.Helliesen (1890) described his Deronectes maritimus from boldly marked material from coastal rock pools on Tjøme and near Hankø in southern Norway, and considered the paler, more clearly striped form from the southern Norwegian mountains (Gaustafjeld, Mjøsvand and Valders) to be the true S. griseostriatus of De Geer.Falkenström (1922) showed that De Geer's S. griseostriatus was in fact the boldly marked Swedish Baltic coastal form, and proposed the name S. multilineatus for the inland form, placing it as a variety of S. griseostriatus De Geer.He gave only a brief description and made no mention of type material, but simply referred to Helliesen's publication.Later (Falkenström, 1929) he raised S. multilineatus to species rank and gave a detailed description and fi gures, but this is not the original use of the name, and in any event, no type was designated.Much of Helliesen's collection belongs to the Natural History Museum in Stavanger (Norway), and is at present on loan to the museum at Trondheim, where it is being curated.
There is also material in the Zoological Museum in Oslo.However, there is no material of "maritimus" from the localities mentioned by Helliesen, in either of these collections.There is, however, one female "griseostriatus" in the Oslo collection, labelled "Gausta" (a handwritten label) and "Helliesen" (a printed label).
Gaustafjeld is one of the localities from which Helliesen recorded his S. griseostriatus, so this specimen is part of the material for which Falkenström proposed the name Potamodytes multilineatus.It is therefore a syntype of Potamodytes multilineatus.It is a female, 4.3 mm long, with the elytra yellowish with distinct and well-separated blackish stripes, and the pronotum with the sides weakly but evenly curved, as in Nilsson and Holmen's habitus fi gure of S. multilineatus (Nilsson, Holmen, 1995, Fig. 347).Stripy S. griseostriatus, from Finnish Lapland and the Alps, has the pronotum with the sides straight over most of their length but then curved inwards in the basal fi fth, as in Nilsson and Holmen's habitus fi gure of S. griseostriatus (Fig. 347).Thus both the morphology and the geographical origin of this specimen are in accord with its being S. multilineatus as currently interpreted.After discussion with Dr A. N. Nilsson (Umeå, Sweden), the leading Scandinavian expert on Dytiscidae, I am leaving this specimen as a syntype just in case a male syntype should be discovered somewhere, and am designating a neotype for Deronectes maritimus Helliesen as it seems very unlikely that type material still exists.The neotype is from the material I collected on Tjøme.The discovery of true S. griseostriatus in the Alps was completely unexpected since all previously analysed material had belonged to other species of the S. griseostriatus group (Dutton, Angus, 2007).A map showing the known distributions of the S. griseostriatus group species in the Alps is given as Fig. 2, drawing on the data given by Dutton, Angus (2007) as well as those presented in this paper.Four species are involved.S. griseostriatus itself appears to be distributed over the main spine of the Alps, from Bavaria in the east to western Switzerland in the west.S. alpestris Dutton et Angus, 2007, inhabits the southern edges of the Alps, from the Italian Dolomites in the east to Ticino (Switzerland) in the west -and possibly further west, but no information is available.S. ibericus, an inhabitant of all the Iberian mountain ranges (Dutton, Angus, 2007), is found in the Maritime Alps and as far north as Briançon.It is interesting, but not surprising, that this is the species found on Corsica.The Alpine species with the most restricted known distribution is S. inexpectatus Dutton et Angus, 2007.This is still known only from the smaller of the two Lauzet lakes (Lac du Lauzet inférieur), while the larger lake, only about a kilometre distant, has S. ibericus.Clearly, more information on the S. griseostriatus group in the western French Alps is needed.
As yet there appear to be no records of the S. griseostriatus group from the arc of mountains running north and east of the Alps, the "Mittelgeberge" -the Sudeten Mountains, the Tatra and the Carpathians, though the High Ta- tra, at least, appears to offer suitable habitats.However, even if the beetles do occur in some of these mountains, there is still a very large gap between their northern and Alpine distributions.The Starunia fossil material, from the Carpathians, may be true S. griseostriatus, and while this does not signifi cantly close the gap between the northern and Alpine distributions, it does show that these beetles have been present in the area for thousands of years.
., 2010 4(1) Comparative Cytogenetics within the S. griseostriatus group.However, the paramere (Fig. 5, c), although squashed and somewhat broadened artifi cially, does bear a reasonable resemblance to the modern Norwegian S. griseostriatus (Fig. 5, d), suggesting that it might in fact be true S. griseostriatus.The fossil elytron matches the paler striped Swiss material from the silty pool near Le Louché.Coleoptera from Starunia at present in my possession.The material comprises one right elytron, about 3.6 mm long and with very distinct brown (faded) stripes on a pale background, and one abdomen complete with aedeagophore.The aedeagus, laterally compressed, and one paramere, also compressed, are shown in Fig. 5, with modern Scandinavian S. griseostriatus for comparison.The aedeagus (Fig. 5, a) is similar in size and shape to the modern Swedish specimen (Fig. 5, b), but is not suffi ciently distinctive to allow identifi cation

Table 1 .
Material used for chromosomal analysis.