Ecosystem shifts at two mid-Holocene tipping points in the alpine Lake Son Kol (Kyrgyzstan, Central Asia)

Tipping points can be defined as critical ecosystem thresholds that start self-enforced dynamics pushing systems into new stable states. Many lake ecosystems of arid Central Asia are sensitive to hydrological changes as they are located at the intersection of the influence of the dry Siberian Anticyclone and the relatively humid mid-latitude Westerlies, and their sediment records can be used to study past tipping points. We studied subfossil chironomid remains preserved in a ca. 6000-year-long sediment record from the Central Asian lake Son Kol (Central Kyrgyzstan) to reconstruct past ecosystem dynamics. Our results show abrupt transitions from a chironomid fauna dominated by macrophyte-associated, salinity-indicating taxa, to a vegetation-independent fauna, and subsequently to a macrophyte-associated, freshwater-indicating fauna. A comparison of the chironomid-based environmental reconstruction to other proxy indicators from the same record suggests a phase of increased Westerly strength starting about 4900 cal. yr BP. This increase led to enhanced precipitation and sediment fluxes into the lake, which in turn led to high turbidity levels and consequently to a macrophyte collapse causing abrupt changes in the chironomid fauna. At 4300 cal. yr BP, a weakening of the Westerlies in combination with higher lake levels led to lower turbidity and ultimately to the recovery of the macrophyte population and associated changes in the chironomid assemblage. These two sequences of events show how the occurrence of a gradual change in an external trigger (Westerlies) can trigger a cascade of within-lake processes (turbidity, macrophyte density) and may ultimately lead to an abrupt reorganization of the ecosystem (chironomid fauna), providing models for tipping points.

Chironomids (Insecta, Diptera, Chironomidae) from alpine lakes in the Eastern Carpathians with comments on newly-recorded species from Ukraine

The first summarising checklist of Ukrainian Chironomidae (Insecta, Diptera) consisted of 302 species. Compared to other European countries, it is obvious that the real chironomid diversity of Ukraine has not been fully documented and greater effort is needed to discover the actual richness of this family. Thus, our survey focused on the chironomid fauna of some alpine lakes situated above the treeline in the Ukrainian Carpathians (a part of the Eastern Carpathians) aiming to contribute to the knowledge of the Ukrainian chironomid fauna and create the basis for more comprehensive neo- and palaeolimnological studies of these, regionally, little-known ecosystems. In total, 34 species/taxa, belonging to 22 genera and 4 subfamilies were collected in June 2019. Ten species were recorded for the first time in Ukraine: Zavrelimyia melanura, Acamptocladius reissi, Cricotopus speciosus, Cricotopus curtus, Heterotrissocladius marcidus, Orthocladius dentifer, Psectrocladius oligosetus, Polypedilum uncinatum, Paratanytarsus laccophilus and Tanytarsus bathophilus. The occurrence of six species previously considered as “doubtfully present” in Ukraine was finally confirmed. Generally, the surveyed lakes have a unique composition of chironomids consisting of a mixture of species typical for cold alpine lakes and acidic ponds situated at lower altitudes.

DNA barcode data reveal biogeographic trends in Arctic non-biting midges

Chironomid flies (non-biting midges) are among the most abundant and diverse animals in Arctic regions, but detailed analyses of species distributions and biogeographical patterns are hampered by challenging taxonomy and reliance on morphology for species-level identification. Here we take advantage of available DNA barcode data of Arctic Chironomidae in BOLD to analyse similarities in species distributions across a northern Nearctic – West Palearctic gradient. Using more than 260 000 barcodes representing 4666 BINs (Barcode Index Numbers) and 826 named species (some with interim names) from a combination of public and novel data, we show that the Greenland chironomid fauna shows affinities to both the Nearctic and the West Palearctic regions. While raw taxon counts indicate a strong Greenland – North American affinity, comparisons using Chao’s dissimilarity metric support a slightly higher similarity between Greenland and West Palearctic chironomid communities. Results were relatively consistent across different definitions of species taxonomic units, including morphologically determined species, BINs, and superBINs based on a ∼4.5% threshold. While most taxa found in Greenland are shared with at least one other region, reflecting circum-Arctic dispersal, our results also reveal that Greenland harbours a small endemic biodiversity. Our exploratory study showcases how DNA barcoding efforts using standardized gene regions contribute to an understanding of broad-scale patterns in biogeography by enabling joint analysis of public DNA sequence data derived from diverse prior studies.

Sub-fossil Chironomidae (Diptera) from lake sediments in Central America: a preliminary inventory

The chironomid diversity of Central America is virtually underestimated and there is almost no knowledge on the chironomid remains accumulated in surface sediments of lakes. Thus, in the present study we provide information on the larval sub-fossil chironomid fauna from surface sediments in Central American lakes for the first time. Samples from 27 lakes analysed from Guatemala, El Salvador and Honduras yielded a total of 1,109 remains of four subfamilies. Fifty genera have been identified, containing at least 85 morphospecies. With 45 taxa, Chironominae were the most specious and also most abundant subfamily. Tanypodinae with 14 taxa dominated in about one third of the sites. Orthocladiinae were presented by 24 taxa, but were recorded in 9 sites, being dominant in only one site. Podonominae were collected only in one locality. Head capsules of Heterotrissocladius found in the high elevation lake Magdalena, Guatemala, represent a first record for the Neotropical region. Both relative abundance and species richness of Chironominae and Orthocladiinae showed significant relationship to elevation, while Tanypodinae were indifferent. Hopefully, the list of taxa provided by our study will be a base line for future limnological and paleolimnological investigations using chironomid remains in the region.

Mayfly (Ephemeroptera) assemblages of a Pannonian lowland mountain, with first records of the parasite Symbiocladius rhithrogenae (Zavrel, 1924) (Diptera: Chironomidae)

Despite increasing numbers of studies on aquatic insects in South-East European streams, there are still gaps in the knowledge about their distribution and assemblage composition in many regions. As one of the most abundant and sensitive aquatic insects, mayflies are widely used as bioindicator taxa. With the main goal of improving the knowledge of South-East European mayflies, a study was conducted of 15 streams along a Pannonian lowland mountain, in spring and summer 2017. A total of 18 mayfly taxa were recorded, where Ephemera danica Müller, 1764 and Baetis rhodani (Pictet, 1843) were the most widespread. All sites were characterized with the domination of rhithral elements, with similar shares of grazers/scrapers and detritivores. Nevertheless, sites at lower altitudes generally had a higher share of potamal and littoral elements, and a higher share of detritivores than at higher altitudes. NMDS analysis separated sites mainly based on sampling period. Although Heptageniidae nymphs were recorded in all streams, the parasitic chironomid Symbiocladius rhithrogenae (Zavrel, 1924) was recorded attached to three nymphs of Rhithrogena group semicolorata, each in a different stream. These records represent the first report of this species for Croatia. The current study contributes significantly to our knowledge of mayfly assemblages and species distribution in South-East Europe. Moreover, with a newly recorded species, this study indicates that the knowledge of the Croatian chironomid fauna is still growing.