Holocene insect remains from south-western Greenland

Abstract

Remains of plants and invertebrates from Holocene deposits in south-western Greenland include a number of insect fragments from Heteroptera and Coleoptera. Some of the finds extend the known temporal range of the species considerably back in time, and one of the taxa has not previously been found in Greenland either fossil or extant. The fossil fauna includes the weevil Rutidosoma globulus which is at present extremely rare in Greenland. Its rarity might indicate that it is a recent immigrant, but the fossil finds provide a minimum date for its arrival at around 5840 cal. years B.P. Other remains of terrestrial insects complement the scarce fossil Greenland record of the species concerned.

• Greenland
• Arctic
• Holocene
• insects
• beetles
• palaeoenvironments

The history of the Greenland flora and fauna has been much debated, especially regarding survival in ice-free areas during the last ice age versus immigration after the last partial deglaciation of Greenland. In his review, Bennike (1999) concluded that most species immigrated after the last deglaciation. This was mainly based on two arguments: (1) According to temperature reconstructions, the mean annual air temperature in Greenland was around 23°C lower than at present during the last glacial maximum ca. 25 000 years before present (Dahl-Jensen et al. 1998). It was argued that only few hardy species of vascular plants or animals would be able to cope with such harsh conditions. (2) The Greenland Ice Sheet was much larger during the last glacial maximum than at present, and the margin reached the edge of the continental shelf (Vinther et al. 2009), leaving only comparatively small ice-free areas on mountains and in certain lowland areas (Funder 1979; Funder et al. 2011). It is noteworthy that the ground beetle Amara alpina that is well adapted to Arctic conditions and was widespread in Greenland during the last interglacial stage (Böcher 1989; Bennike & Böcher 1994; Bennike 2002) apparently did not survive the last ice age. Nevertheless, it must still be emphasized that the microclimate, especially on south-facing slopes, must have created fairly favourable conditions, regardless of the low mean-temperature. The fact that the sun stays permanently above the horizon during summer in large parts of Greenland also helps to maintain fairly high temperatures locally.

During the past decades, insect remains have been studied from Late Pliocene/early Pleistocene and last interglacial deposits in Greenland (Bennike & Böcher 1994; Böcher 1995; Brodersen & Bennike 2003). Deposits of Holocene age have also been analysed (e.g., Böcher & Fredskild 1993; Böcher & Bennike 1996; Bennike et al. 2000), but Holocene lake, mire and river deposits offer a large potential for further work on insect remains. Such work can help unravel environmental and climatic changes, but also shed light on the history of the insects and providing data on their temporal range in Greenland. The present fauna of Greenland Coleoptera has been treated by Böcher (1988). Here we report on some insect remains that were found in Holocene sediment samples from the Sisimiut region in south-western Greenland (Figs. 1, 2).

Fig. 1  Map of Greenland showing the location of Sisimiut and other places mentioned in the text.

Fig. 2  Detailed map of the Sisimiut area showing the position of the sampled lakes.

Setting

The samples were collected near the outer coast in south-western Greenland (Figs. 1, 2). This region belongs to the low-arctic bioclimatic zone. The mean July temperature was 6.3°C and the mean annual precipitation 383 mm during the period from 1961 to 1990 (Cappelen et al. 2001). Permafrost is discontinuous. The local bedrock is dominated by glacially scoured Precambrian crystalline basement gneiss. Thin Quaternary till and gravel deposits are widespread. The topography is rugged with abundant lakes, and the highest mountain in the area is 554 m a.s.l. The vegetation is dominated by moss-rich scrubs and heaths with Salix glauca, Betula nana and ericaceous dwarf shrubs such as Empetrum nigrum and Ledum palustre. Fens, bogs and snow-bed vegetation are widespread on poorly drained sites and the uplands are characterized by fell-field vegetation. The terrestrial insect fauna includes around ten species of beetles (Böcher 1988).

The samples come from lake sediment cores collected from unnamed lakes, here referred to as Sisi 12, Sisi 14 and Sisi 15, located north north-west of Sisimiut (Holsteinsborg). Sisi 12 is located at ca. 200 m a.s.l., and the 341-cm long sequence was collected at 66°58.925′N, 53°43.090′W, at a water depth of 7.7 m. Sisi 14 is located at ca. 185 m above sea level, and the 440 cm long sequence was collected at 66°58.786′N, 53°44.005′W, at a water depth of 7.3 m. Sisi 15 is situated 129.9 m a.s.l. The core from this lake was collected at 66°57.72′N, 53°40.55′W, at a water depth of 5.6 m. The core was 356 cm long, but the insect remains discussed here come from the upper part of the core, which was relatively rich in macroscopic remains of terrestrial plants. This is probably because a small delta to the north of the lake prograded towards the core site during the Holocene. A small section ca. 0.5 m high that was eroded in the onshore delta sediments revealed fine-grained sand and silt with a thin organic-rich layer, from which a sample was also collected. The latter sample consisted of fine-grained sand, whereas the other samples consisted of gyttja (lake mud).

Methods

Sediment cores were collected with a Russian corer and sub-sampled in the laboratory. Small sub-samples around 15 ml were wet-sieved, and the residue left on the sieves was studied using a dissecting microscope. For insect analyses such samples are small, but this was balanced by a large number of analysed samples (830). A 2-kg sample was collected from an open section in the delta at Sisi 15 and also wet-sieved and analysed.

Samples of terrestrial plant macrofossils were dated using accelerator mass spectrometry radiocarbon age determination. The dates have been calibrated to calendar years according to the INTCAL09 data set. The sequence from Sisi 12 was dated on the basis of five age determinations, the sequence from Sisi 14 on the basis of six age determinations and the sequence from Sisi 15 on the basis of five age determinations. All gave well constrained age-depths curves that have enabled us to put ages on the recovered insect remains (Fig. 3). The remains from the delta at Sisi 15 were dated on the basis of an age of 3725±50 ¹⁴C years B.P. (LuS-8463; date based on Salix herbacea leaves). This corresponds to a calibrated age of 4236–3959 cal. years B.P., or ca. 4100 cal. years B.P.

Fig. 3  Age–depth curves for Sisi 12, Sisi 14 and Sisi 15.

Results

A number of fragments of Heteroptera (true bugs) and Coleoptera (beetles) were found in the samples (Fig. 4). This is not by itself sensational, but the evidence provided about their former presence in south-western Greenland is highly interesting. Here we present some notes on the species recorded.

Fig. 4  Temporal ranges of insect taxa from the Sisimiut region discussed in this paper.

Nysius groenlandicus (Zetterstedt, 1838) (Heteroptera: Lygaeidae)

One head and seven prothoraces, with ages between 9140 and 3515 cal. years B.P., were collected. The Greenland seed bug is common and found almost throughout the ice-free parts of Greenland, with increasing abundance from the coast inland, reflecting the extreme thermophily and xerophily of the species. It is a polyphagous seed-feeder with a single yearly generation and overwintering in the egg-stage (Böcher 1972, 1975, 1976; Böcher & Nachman 2001, 2010). The distribution is palaearctic and Arctic–alpine, at least covering Iceland and Scandinavia, Arctic Russia and (apparently) Asian mountains. An occurrence in sub-Arctic North America has still to be confirmed (Danks 1981).

Nysius groenlandicus was present in Jameson Land, east Greenland and the Thule region, north-west Greenland, during the last interglacial stage (Bennike & Böcher 1992, 1994) and recorded from early Holocene deposits in north-eastern Greenland (Böcher & Bennike 1996; Christiansen et al. 2002). The earliest Holocene records are dated to ca. 9800 cal. years B.P. (west Greenland) and 8700 cal. years B.P. (east Greenland). The finds from the Sisimiut region confirm that N. groenlandicus was an early member of the Holocene fauna of Greenland. Remains of the species have been recorded from a large number of mid- and late Holocene deposits in Greenland (Buckland et al. 1983; McGovern et al. 1983; Böcher & Fredskild 1993; Böcher 1998; Bennike 2000; Bennike et al. 2000; Wagner et al. 2008; Buckland et al. 2009; Bennike, Knudsen et al. 2010).

Bembidion grapii (Gyllenhal, 1827) (Coleoptera: Carabidae)

Two front halves of right elytra of this ground beetle were found, with ages around 8855 and 4680 cal. years B.P. The species is fairly common in west Greenland, has been found northwards to 72°20′N and is therefore the only Greenland carabid extending almost to the High Arctic. In east Greenland its occurrence seems to be much more scattered northwards to ca. 69°N. The general distribution is circumpolar, low Arctic and sub-Arctic, mostly in alpine regions. B. grapii preferably lives in fairly warm and dry situations, e.g., among low vegetation or in birch coppices on south-facing slopes.

As a fossil in Greenland B. grapii has been recorded from central east Greenland (early Holocene; Böcher & Bennike 1996), south-east Greenland (late Holocene; Hasholt 2000), west Greenland (mid-Holocene; Böcher & Fredskild 1993; Bennike et al. 2000) and south Greenland (Buckland et al. 2009).

Hydroporus morio (Aubé, 1823) (Coleoptera: Dytiscidae)

One right elytron, two left elytra and two meso + metasterna were found in sediments from Sisi 14, with ages between 5840 and 2205 cal. years B.P. The small of the two Greenland predacious water beetles is very common and widely distributed along the western coast, at least north to Thule Air Base at 76°30′N. The species is also common in south-east Greenland, recorded north to 65°N. H. morio inhabits any kind of small ponds and pools, frequently temporary pools, and also marshes, but shallow ponds with a muddy bottom are preferred. The species is circumpolar, Arctic to northern temperate.

In Greenland, remains of H. morio have been found in last interglacial deposits (Bennike & Böcher 1994) and in Holocene deposits (Fredskild et al. 1975; Fredskild 1983, 1985; Buckland et al. 1983; Böcher & Fredskild 1993; Bennike 1995, 2000; Eisner et al. 1995). The oldest Holocene finds of the species are dated to around 9500 years old (Fredskild et al. 1975; Fredskild 1983).

Colymbetes dolabratus (Paykull, 1789) (Coleoptera: Dytiscidae)

Many fragments of elytra were found in the sediments from Sisi 12 and Sisi 14, with ages between 6570 and 3740 cal. years B.P. C. dolabratus is the largest beetle in Greenland and abundant in the southern half of the country, with a northern limit in the southern High Arctic at ca. 74°N in both west and east Greenland. This is a circumpolar species with an Arctic to northern temperate range.

The species typically lives in ponds with rich vegetation, but it is highly eurytopic and may be present in almost any kind of stagnant water where larvae and adults are found together during the summer. In late summer the imagines migrate to hibernate in lakes that do not freeze to the bottom. During winter the species depends on diffusion of oxygen into the air bubble under the elytra. The air bubble decreases in size if not replenished, and if the lake is ice covered for extended time the imagines may suffer from lack of oxygen. The northern limit in Greenland is probably determined by the length of the period of ice cover.

Remains of C. dolabratus have been reported from many Holocene sites in Greenland (Fredskild et al. 1975; Fredskild 1985; Böcher & Fredskild 1993; Björck et al. 1994; Bennike 1995, 2000; Eisner et al. 1995; Bennike & Funder 1997; Bennike et al. 1999; Bennike, Anderson et al. 2010). The oldest remains are dated to ca. 10 800 cal. years B.P. (east Greenland; Björck et al. 1994) and ca. 9500 cal. years B.P. (north-west Greenland; Fredskild 1985). Both species of predaceous diving beetles were among the first insects to appear in Greenland following the last partial deglaciation.

Micralymma brevilingue (Schiödte, 1845) (Coleoptera: Staphylinidae)

One pronotum, two left elytra and one set of paired elytra were found in sediments from Sisi 14, and dated to ca. 2205–200 cal. years B.P. M. brevilingue is the most widespread rove-beetle in Greenland, found even in the southern part of the High Arctic and very commonly along the western coast. In most cases the species lives close to the beach. It can also be found elsewhere, for example, in snow-beds and luxuriant herbslopes. The species is circumpolar and Arctic. According to Makarova et al. (2007) the species is widespread in the High Arctic archipelago of Severnaya Zemlya, Siberia, and is thus the northernmost occurring beetle-species in Eurasia.

Fossil M. brevilingue have been reported from south-west Greenland (Bennike 1992; Böcher & Fredskild 1993; Böcher 1998). The finds are middle to late Holocene in age.

Atheta cf. islandica (Kraatz, 1856) (Coleoptera: Staphylinidae)

One left and one right elytron, dated to 9110 and 7040 cal. years B.P. were found. The genus Atheta comprises four Greenland species of which A. (Boreophilia) islandica seems to be most common and to have the greatest geographical range in Greenland (north to 68°40′N in west Greenland and 63°N in east Greenland). The species is palaearctic and Arctic–alpine.

Remains of another species, Atheta (Boreophilia) hyperborea Brundin, 1940 were found fairly frequently in palaeo-Eskimo sediments from Disko Bugt (Böcher & Fredskild 1993), but it is highly surprising to find the genus as early as 9110 cal. years B.P.

Bledius sp. (Coleoptera: Staphylinidae)

One right elytron was found in the sediment sequence from Sisi 12, dated to around 2730 cal. years B.P. The large genus Bledius primarily comprises small species living in burrows on mud-flats. The find is important because the genus has never before been reported from Holocene Greenland deposits and is unknown from the modern-day fauna of Greenland. It was, however, recorded from the early Quaternary Kap København and Store Koldewey Formations in north and north-east Greenland, both dated to around 2 Mya (Böcher 1995; Funder et al. 2001; Bennike, Knudsen et al. 2010).

Simplocaria metallica (Sturm, 1807) (Coleoptera: Byrrhidae)

Two heads, five left elytra (four fragments) and four right elytra (two fragments) of this pill beetle were found, dated to between 9920 and 4100 cal. years B.P. The species is fairly common in western Greenland south of Disko, although occurring scattered; also found locally in south-eastern Greenland. S. metallica is undoubtedly a moss-feeder, always found in the vicinity of water. It is of circumpolar distribution, Low Arctic to northern temperate, alpine in southern Europe.

Simplocaria metallica has hitherto been recorded from mid- and late Holocene deposits in southern and western Greenland (Buckland et al. 1983; Böcher & Fredskild 1993; Böcher 1998; Bennike et al. 2000; Buckland et al. 2009) and also from the last interglacial stage in central east Greenland (Bennike & Böcher 1994). Previously the oldest (Holocene) find was dated to ca. 5800 cal. years B.P. Hence the present records extend the known temporal Holocene range far back in time, and the find dated to 9920 cal. years B.P. is the oldest record of a terrestrial beetle species from Holocene deposits in Greenland.

Byrrhus fasciatus (Forster, 1771) (Coleoptera: Byrrhidae)

One pronotum was recorded from the delta deposit dated to ca. 4100 cal. years B.P. B. fasciatus is common and widespread in Greenland, reaching the High Arctic in both west and east Greenland. The species is circumpolar and like S. metallica a moss-feeder found in highly different, both humid and dry situations. Both larva and adult feed on mosses. The distribution is circumpolar, Low-Arctic to temperate.

Fragments of B. fasciatus have been found in last interglacial deposits (Bennike & Böcher 1994) and in mid- and late Holocene sediments in south-western Greenland (Buckland et al. 1983; Böcher & Fredskild 1993). The earliest Holocene record (from Disko Bugt) is about 4400 cal. years old.

Rutidosoma globulus (Herbst, 1795) (Coleoptera: Curculionidae)

One prothorax, two left elytra and two right elytra were found (Fig. 5), dated to between 5840 and 3300 cal. years B.P. The sculpture of the fossil specimens seems to be a little less pronounced than that of recent specimens, but the identification has been confirmed by Robert Anderson (pers. comm. 2008). The present distribution of Rutidosoma globulus comprises most of northern and central Europe, but it is absent from the Faroe Islands and Iceland. In Denmark Rutidosoma globulus is a rare species (Hansen 1964). In Europe it is monophagous on Populus tremula (Hoffman 1958; Bullock 1992).

Fig. 5  Rutidosoma globulus (Herbst, 1795), a modern Greenland specimen drawn by Robert Nielsen.

In Greenland R. globulus appears to be extremely rare, and only three extant specimens are known. In addition to an old find from an unknown locality, one specimen was collected in the fjord Søndre Isortoq in 1885. During fieldwork in 2003 another specimen was found in the same fjord by sweeping in a small valley with snow patch vegetation comprised of Salix herbacea, S. arctophila, S. glauca, Polygonum viviparum and Carex spp. Populus does not grow in Greenland, and the food plant here is probably one or more species of Salix.

The only previous fossil record of R. globulus in Greenland is of late Holocene age and comes from a Norse ruin in Nuup Kangerlua (Godthåbsfjord; McGovern et al. 1983). It is indeed surprising to find an apparently rare species to be fairly numerous in the fossil material.

Discussion and conclusion

The colonization of Greenland by insects, especially beetles (Coleoptera) following the last ice age has been the object of a long-lasting debate which is by no means finished. However, these new finds add some facts to the discussion.

The rare Greenland occurrence of the weevil Rutidosoma globulus might suggest that the species is a fairly recent immigrant which has not yet had time to spread over large areas. If it feeds on willow (Salix spp.) one would assume that it has plenty of opportunities in Greenland, as willows are common and widespread. The fossil finds reported here provide a minimum date for its arrival in Greenland at around 5840 years B.P. ago, and it is surprising that it is so rare. It is a possibility that Salix spp do not constitute an optimal diet for the species.

Most of Greenland's terrestrial beetle species arrived from north-west Europe, in many cases using the Faroe Islands and Iceland as stepping stones. It is clear from its modern geographical range that Rutidosoma globulus also arrived from Europe, but the species does not occur in the Faeroe Islands or Iceland, so in some way it must have dispersed directly across the North Atlantic Ocean.

In general, the data from the Sisimiut region combined with other data from Greenland imply that many insect species were present in the early Holocene. This could be used as an argument in favour of survival in Greenland during the last glacial stage. However, large areas were deglaciated during the late Weichselian, from around 15 000–12 000 cal. years B.P. (e.g., Björck et al. 2002; Kelly et al. 2008). During this time period many plant and animal species may have immigrated to Greenland. We conclude that fossil finds to date do not tell us whether some insect species survived in Greenland during the last glacial stage.

Acknowledgements

OB is grateful to the Carlsberg Foundation for funding. Robert S. Anderson, Canadian Museum of Nature, Ottawa, kindly scrutinized the Rutidosoma elytra. Alexey Solodovnikov, at the Zoological Museum, Natural History Museum of Denmark, University of Copenhagen, is thanked for identifying a pronotum of Micralymma brevilingue.