Chironomid Larvae Research Articles

Relationship between heavy metals and dissolved organic matter released from sediment by bioturbation/bioirrigation

Organic matter (OM) is an important component of sediment. Bioturbation/bioirrigation can remobilize OM and heavy metals that were previously buried in the sediment. The remobilization of buried organic matter, thallium (Tl), cadmium (Cd), copper (Cu) and zinc (Zn) from sediment was studied in a laboratory experiment with three organisms: tubificid, chironomid larvae and loach. Results showed that bioturbation/bioirrigation promoted the release of dissolved organic matter (DOM) and dissolved Tl, Cd, Cu and Zn, but only dissolved Zn concentrations decreased with exposure time in overlying water. The presence of organisms altered the compositions of DOM released from sediment, considerably increasing the percentage of fulvic acid-like materials (FA) and humic acid-like materials (HA). In addition, bioturbation/bioirrigation accelerated the growth and reproduction of bacteria to enhance the proportion of soluble microbial byproduct-like materials (SMP). The DOM was divided into five regions in the three-dimensional excitation emission matrix (3D-EEM), and each part had different correlation with the dissolved heavy metal concentrations. Dissolved Cu had the best correlation with each of the DOM compositions, indicating that Cu in the sediment was in the organic-bound form. Furthermore, the organism type and heavy metal characteristics both played a role in influencing the remobilization of heavy metal.

БИОЛОГИЧЕСКАЯ ОЦЕНКА МАЛЫХ ВОДОЕМОВ, РАСПОЛОЖЕННЫХ В ПАРКОВЫХ ЗОНАХ ГОРОДА МОСКВЫ

The article describes the biological and ecological state of ponds of three park zones located in northern, central and western administrative districts of Moscow. The area of reservoirs varied from 0.12 to 3.71 ha, average depth varied from 1.12 to 2.4 m. The analysis of hydrobiological material in accordance with existing criteria has been carried out. Total and seasonal concentration and biomass of phytoplankton, zooplankton and benthos are determined. During observation period in composition of algocenosis prevailed representatives of following groups of algae: Volvocophyceae, Desmidiales, Bacillariophyta, Xanthophyta, Zygnematophyceae, Chrysophyta, Pyrrophyta, Protococcophyceae, Cyanophyta, Euglenophyta. Concentration of algae in ponds varied from 0.58 up to 6.78 mln/l, total biomass varied from 0.87 to 9.70 mg/l. Zooplankton of the inspected ponds was represented by species of three systematic groups: Rotatoria, Cladocera and Copepoda. Concentration of zooplankton organisms varied from 0.0055 to 3.9432 mln/m3, biomass varied from 0.05 to 18.60 g/m3. Zoobenthos included Oligochaeta, Clitellata and insect larvae (Chironomidae, Ephemeroptera, Trichoptera). Prevalence of various representatives of plankton groups depended on the season of the year. In zoobentos samples there were found oligochaeta, chironomid and mayfly larvae, caddisflies and leeches. Higher plants were represented by 8 hydrophytic species, 1 species with floating leaves and 10 aerial coastal species. Ichthyofauna of ponds included 12 species among which aborigen species were common carp, crucian carp, roach, bream, tench, verkhovka, Amur sleeper, pike, perch, pike-perch; invasive species were grass carp, silver carp. The investigations of the large Golytsinsky pond have demonstrated that episodic releases of silver carp (spotted and hybrid) make possible to utilize both zooplankton and phytoplankton, and release of grass carp helps utilize higher water plants.

Unexpected patterns of chironomid larval size in an extreme environment: a highly glaciated, alpine stream

In this article, we report on the development and growth of alpine chironomid species in a highly glaciated headwater, using biometrical analyses. Glacially influenced alpine streams are characterized by year-round harsh environmental conditions. Only a few, highly adapted benthic insects, mainly chironomid larvae (genus Diamesa) live in these extreme conditions. Although several studies have shown patterns in ecosystem structure and function in alpine streams, cause–effect relationships of abiotic components on aquatic insects’ life strategies are still unknown. Sampling was performed at Schlatenbach, a river draining the Schlatenkees (Hohe Tauern NP, Austria), at three sites and on six occasions from August to October 2015. Semi-quantitatively sampled Diamesa cinerella (Meigen 1835) and Diamesa steinboecki (Goetghebuer 1933) larvae were biometrically analysed, and they showed differences in larval size and biovolume with higher values close to the glacier. Considering the decreasing water temperatures but increasing benthic organic matter towards the glacier, food availability seems to play a crucial role for larval size in highly glaciated alpine headwaters. This is the first study to show that harsh conditions in these environments (low temperatures, high turbidity and flow dynamics) may exclude many taxa, but favour other, highly adapted species, when their essential needs (food quality and quantity) are guaranteed.

Family Variation of Aquatic Insects and Water Properties to Assess Freshwater Quality in El-Mansouriya Stream, Egypt

The use of family variation of aquatic insects in assessing freshwater quality in ecosystems has only recently been applied in the northern parts of Africa. The current study along with El Husseiny et al. (2015) and Bream et al. (2017) can be considered the first of such studies in Egypt. The survey was conducted during the period April 2015 to February 2016, in the permanent stream, El-Mansouriya, in Dakahlia province, Egypt. The water quality and health status of water for human use of this stream was determined using different aquatic invertebrate family biotic indices formulations (BMWP, SWRC and EPT indexes) along with the physical and chemical properties. Water samples were analysed and the water quality parameters were compared to the WHO (2004) standards. Most of the parameters were found to be within permissible limits, except for turbidity and nutrient salts. Aquatic insects were collected and identified to order and family levels. A total of seven orders and 19 families were collected, including a few intolerant insects (EPT orders) and insects more tolerant to pollution (chironomid larvae). The values of the water quality parameters sampled showed significant correlations with aquatic insect diversity. The canonical correspondence analysis clarified that the electrical conductivity of the water was the most significant variable affecting the variation in taxa. From these results it can be seen that the water quality of this stream is moderately impacted, and could therefore be considered harmful, since this stream is the main supply to the Water Central Station in Aga. Water quality degradation is generally due to impacts associated with population growth, industrialisation and agricultural activities. These results can be used to assist in conservation planning and decision-making in Egypt.

Food habits of fishes in a freshwater reed belt in Lake Kitaura, eastern Japan, in summer

The diets and feeding guild structure of a freshwater reed belt fish assemblage (30 species) were examined in Lake Kitaura, part of the Lake Kasumigaura system, eastern Japan, from June to September in 2009 and 2010. Ontogenetic dietary shifts were recognized in 14 species, including several species (e.g., Cyprinus carpio, Tridentiger brevispinis and Hyporhamphus intermedius) targeted by local fisheries. Juveniles of these species generally fed on zooplankton, later switching to other prey items (e.g., benthic chironomid larvae, gammaridean amphipods, shrimps, juvenile fishes, diatoms and decomposing reeds) with growth. A cluster analysis based on dietary overlaps showed that the reed belt fish assemblage comprised five feeding guilds (plant, zooplankton, benthic invertebrate, terrestrial insect and fish feeders). Of these, zooplankton feeders were the most abundantly represented in terms of species numbers, suggesting that the main food items for the fish assemblage were zooplankton (e.g., cladocerans, and calanoid and cyclopoid copepods). Fish feeders included five species, of which one was an alien species introduced from another region in Japan (Opsariichthys uncirostris) and three were from foreign countries (Micropterus salmoides, Lepomis macrochirus macrochirus and Ictalurus punctatus).

Qualitative and Quantitative Examination of Algal Flora in the Gut Content of <i>Tanypus punctipennis</i> Meigen, 1818

Larval chironomids feed on algae, diatomae, detritus, decaying plant and animal fragments. The larvae in turn are food for other carnivore and omnivore animals. Thus, larval chironomids have a very important role in the aquatic food cycle. In this study, the algal flora in the stomachs of Tanypus punctipennis , which is known as a very common species in Turkish Thrace, was examined in terms of qualitative and quantitative factors. It was found that Bacillariophyta was the dominant group with 43 taxa in the stomach of T. punctipennis. It was followed by Cyanophyta with 7 taxa, Euglenophyta with 6 taxa, Chlorophyta with 4 taxa, Carophyta with 2 taxa, and Rhodophyta with 1 taxa.

Glacier dynamics influenced carbon flows through lake food webs: evidence from a\xa0chironomid \u03b413C-based reconstruction in the Nepalese Himalayas

Using a sediment core covering the last 3,500 years, we analysed photosynthetic pigments’ concentrations in lake sediments and carbon stable isotopic composition of chironomid (Diptera, Chironomidae) remains (δ13CHC). We aimed to reconstruct temporal changes in aquatic primary productivity and carbon resources sustaining chironomid larvae in a high mountain lake (Lake Pyramid Inferior; 5,067 m a.s.l.) located in the Nepalese Himalayas. Both pigments and δ13CHC trends followed a similar fluctuating pattern over time, and we found significant positive relationships between these proxies, suggesting the strong reliance of benthic consumers on the aquatic primary production. Temporal trends matched well with main known climatic phases in the Eastern part of the Himalayan Mountains. Past glacier dynamics and associated in-lake solute concentrations appeared to be the main driver of autochthonous primary productivity, suggesting then the indirect impact of climate change on carbon processing in the benthic food web. During warm periods, the glacier retreat induced a rise in in-lake solute concentrations leading to an increasing primary productivity. Complementary investigations are still needed to strengthen our understanding about the response of past aquatic carbon cycling in CO2-limiting environments.

Most Interesting Findings from Remnants of Chironomid (Insecta: Diptera: Chironomidae) Larvae in Layers of a 200-Year-Old Stratum of Lake Oron Bottom Sediments

The remnants of chironomid larvae from layers of the 10-cm-thick bottom sediment in Lake Oron have been studied. Six taxons unknown in the current chironomid fauna of the lake have been identified: Abiskomyia rivalis, Corynoneura arctica-type, Mesocricotopus thienemanni, Metriocnemus eurynotus-type, Nanocladius rectinervis-type, and Robackia pilicauda. The most probable reasons for the disappearance of these species from the Oron fauna, which are related to environmental changes caused by global climate changes, are considered.

The effect of epiphytic macroinvertebrates on microbial communities in different types of macrophyte-dominated shallow lakes

Complex interactions between epiphytic fauna and microbial food webs in periphyton are vital to the ecosystem ecology of shallow lakes. However, little is known about how different types of macrophyte dominated lakes may influence microbial and metazoan communities. The goal of the present study was to examine the impact of metazoan on microbial food web in three different types of lakes (Stratiotes-dominated,Ceratophyllum-dominated andPotamogeton-dominated). The results of this study suggest a strong correlations between chironomid larvae, small Metazoa and microbial communities in the periphyton of macrophyte-dominated lakes. Weak relations between food web components were found in thePotamogeton-dominated andCeratophyllum-dominated lakes, where environmental variables explained the bulk of the total variance in periphyton abundance, whereas strong predator-prey relations were noted in theStratiotes-dominated lake, where environmental variables had a minor role in the total variance in periphyton abundance. Our study contributes to knowledge of the functioning of eutrophic lakes in the current era of increasing eutrophication caused by climate change and human activity.

МОДЕЛИРОВАНИЕ МНОГОЛЕТНЕЙ ДИНАМИКИ ОБИЛИЯ ПОПУЛЯЦИЙ ЛИЧИНОК CHIRONOMUS PLUMOSUS (L., 1758) И CH. ANTHRACINUS ZETT., 1860 С ПРИМЕНЕНИЕМ ИСКУССТВЕННЫХ НЕЙРОННЫХ СЕТЕЙ (ОЗ. КРАСНОЕ, КАРЕЛЬСКИЙ ПЕРЕШЕЕК, ЛЕНИНГРАДСКАЯ ОБЛАСТЬ)

This article presents the results of a study of long-term series (1964 -1983) of population dynamics of larvae of two species of chironomid of Chironomus plumosus L. and Ch. anthracinus Zett, which dominate the zoobenthos community of the Krasnoye Lake. The main goal of this work is to develop multiple regression models of time-series to predict e dynamics of the number and biomass of populations of two types of chironomids and to assess their predictive ability. The long-term dynamics series were analyzed using the methods of spectral (Fourier) analysis, which made it possible to determine their main harmonic components and evaluate the statistical relationships with the harmonics of the dynamics of chlorophyll concentration “a” in the lake. The article presents the results of forecasting the dynamics of abundance and biomass of chironomid larvae by two types of regression models: using linear multiple regression and regression models using the technology of artificial neural networks. As the results showed, to simulate and predict the time series of the population dynamics of chironomid larvae in the Krasnoye Lake, regression models based on the technology of artificial neural networks turned out to be much more accurate in predictions compared to linear multiple regression models.

Diet of the endangered spirlin (Alburnoides bipunctatus) at the centre of its distribution in Europe

The feeding habits of spirlin Alburnoides bipunctatus were investigated in a tributary of the River Vistula (Poland). To evaluate size-related patterns of resource use, fish were assigned to three size classes, defined according to size at first maturation: small (29–70-mm total length, TL), medium (71–90mm TL) and large (91–104mm TL). There was a significant ontogenetic shift in the feeding pattern among size classes, marked by differences in the proportion of the main taxonomic groups of prey consumed: small spirlin primarily consumed chironomid larvae, whereas medium and large spirlin showed a preference for Coleoptera, Ephemeroptera and imagines of unidentified insects. The proportion of prey taken from the water column was significantly lower for small- than medium- and large-sized spirlin. This difference was attributed to the benthic habits of small spirlin compared with medium and large spirlin. The shift to open water feeding in spirlin corresponded with sexual maturation, with habitat segregation between the smallest size class (comprising juveniles) and larger size classes (mature individuals). Size-specific changes in the diet composition of this species have not previously been documented.

Mouthpart deformities in Chironomidae (Diptera) as bioindicators of heavy metals pollution in Shiroro Lake, Niger State, Nigeria

In this study, mouthpart deformities in Chironomid larvae (Diptera) were investigated in relation to sediment contamination in the Shiroro Lake in Nigeria. Metals and chironomids were sampled monthly at three stations (A–C) between August 2013 and January 2014. Across the stations, zinc ranged (3.9–75mg/g), manganese (1.29–1.65mg/g), lead (0.00–0.10mg/g), iron (101–168mg/g) and copper (0.13–0.17mg/g). The metal ions did not differ significantly (P > 0.05) between the sampling stations. However, zinc and iron ions were significantly different between the sampling seasons (P < 0.05). Thirteen chironomid species were recorded, with Chironomus sp., Polypedilum sp. and Ablabesmyia sp. dominating the assemblage structure. Mouthpart deformities were significantly higher at Station A compared with Station C, and seasonally significantly higher during dry season compared with wet season. Elevated incidences of deformity were recorded in Chironomus spp larvae as compared to other genera therefore for further studies in this region assessments should be based solely on Chironomus species and ignoring the rest. Strategies need to be developed to reduce the contaminations and the biological effects.

Ratio of Methylmercury to Dissolved Organic Carbon in Water Explains Methylmercury Bioaccumulation Across a Latitudinal Gradient from North-Temperate to Arctic Lakes

We investigated monomethylmercury (MMHg) bioaccumulation in lakes across a 30° latitudinal gradient in eastern Canada to test the hypothesis that climate-related environmental conditions affect the sensitivity of Arctic lakes to atmospheric mercury contamination. Aquatic invertebrates (chironomid larvae, zooplankton) provided indicators of MMHg bioaccumulation near the base of benthic and planktonic food chains. In step with published data showing latitudinal declines in atmospheric mercury deposition in Canada, we observed lower total mercury concentrations in water and sediment of higher latitude lakes. Despite latitudinal declines of inorganic mercury exposure, MMHg bioaccumulation in aquatic invertebrates did not concomitantly decline. Arctic lakes with greater MMHg in aquatic invertebrates either had (1) higher water MMHg concentrations (reflecting ecosystem MMHg production) or (2) low water concentrations of MMHg, dissolved organic carbon (DOC), chlorophyll, and total nitrogen (reflecting lake sensitivity). The MMHg:DOC ratio of surface water was a strong predictor of lake sensitivity to mercury contamination. Bioaccumulation factors for biofilms and seston in Arctic lakes showed more efficient uptake of MMHg in low DOC systems. Environmental conditions associated with low biological production in Arctic lakes and their watersheds increased the sensitivity of lakes to MMHg.

On the Diet and Foraging Strategy of Tundra Waders at Sivash

Abstract The feeding on aquatic invertebrates, intensity and efficiency of forage intake were studied at the Sivash lagoons in 1995–2002 by the example of 6 wader species (217 birds). The diet composition significantly varied from seeds of plants to different species of aquatic and soil organisms. The diet at Eastern Sivash was based on Polychaeta, at Central Sivash — on Crustacea and chironomid larvae (Insecta). Foraging intensity depended on the abundance of main prey and the size of prey items taken. We distinguished the studied wader species as “probers” and “gatherers” of forage. The highest foraging intensity among “probers” and “gatherers” were observed at the Sivash lagoons in feeding sites with a high number of chironomid larvae, and the lowest one — in feeding sites with a polychaeta worm Hediste diversicolor. The wader foraging intensity was associated with high density and availability of prey items: at Central Sivash — chironomid larvae and brine shrimps (Artemia salina), at Eastern Sivash — chironomid larvae and polychaetes. Results of the stomach analysis and obtained correlations indicate a determinative role of polychaetes, molluscs, brine shrimps and chironomids in the foraging behaviour and distribution of the studied species of waders at migratory stopovers of the Azov-Black Sea Region.

Habitat modification by invasive crayfish can facilitate its growth through enhanced food accessibility

BackgroundInvasive ecosystem engineers can facilitate their invasions by modifying the physical environment to improve their own performance, but this positive feedback process has rarely been tested empirically except in sessile organisms. The invasive crayfish Procambarus clarkii is an ecosystem engineer that destroys aquatic macrophytes, which provide a physical refuge for animal prey, and this destruction is likely to enhance vulnerability to predators. Using two series of mesocosm experiments, we tested the hypothesis that the invasive crayfish increases its feeding efficiency on animal prey by reducing submerged macrophytes, thus increasing its individual growth rate in a positive density-dependent manner.ResultsIn the first experiment, increasing crayfish density reduced both macrophytes and animal prey (dragonfly and chironomid larvae) and, importantly, increased the growth rate of individual crayfish, in accordance with our expectation. In the second experiment, we used artificial macrophytes to clarify whether the physical architecture of macrophytes itself protects animal prey and limits crayfish growth rate. Increasing the artificial macrophyte quantity not only increased the survival of animal prey, but also retarded the crayfish growth rate.ConclusionsWe conclude that macrophytes strengthen bottom-up control of crayfish, but this effect can be relaxed by increasing the density of crayfish via reduction in macrophytes. This positive feedback process may explain the crayfish outbreaks and regime shifts occasionally observed in invaded freshwater ecosystems.

Microphytobenthos and chironomid larvae attenuate nutrient recycling in shallow‐water sediments

Abstract In shallow‐water sediments, the combined action of microphytobenthos and bioturbating fauna may differentially affect benthic nutrient fluxes and exert a bottom‐up control of pelagic primary production. In many cases, the effects of microphytobenthos and macrofauna on nutrient cycling were studied separately, ignoring potential synergistic effects. We measured the combined effects of microphytobenthos and chironomid larvae on sediment–water fluxes of gas (O2, TCO2 and N2) and nutrients (NH4+, NO3−, NO2−, and SiO2) in shallow‐water sediments of a hypertrophic freshwater lagoon. Fluxes were measured in the light and in the dark in reconstructed sediments with low (L = 600 ind/m2), high (H = 1,800 ind/m2) and no (C) addition of chironomid larvae, after 3 weeks of pre‐incubation under light/dark regime to allow for microalgal growth. Besides flux measurements, pore water nutrient (NH4+, and SiO2) and dissolved metal concentrations (Fe2+ and Mn2+) were analysed and diffusive fluxes were calculated. Chironomid larvae increased sediment heterotrophy, by augmenting benthic O2 demand and TCO2 and N2 dark production. However, on a daily basis, treatments C and L were net O2 producing and N2 sinks while treatment H was net O2 consuming and N2 producing. All treatments were net C sink regardless of chironomid density. Microphytobenthos always affected benthic nutrient exchange, as significantly higher uptake or lower efflux was measured in the light compared with dark incubations. Theoretical inorganic N, P and Si demand by benthic microalgae largely exceeded both dark effluxes of NH4+, and SiO2 and their net uptake in the light, suggesting the relevance of N‐fixation, water column NO3− and solid‐phase associated P and Si as nutrient sources to benthic algae. Chironomid larvae had a minor effect on inorganic N and P fluxes while they significantly stimulated inorganic Si regeneration. Their bioturbation activity significantly altered pore water chemistry, with a major reduction in nutrient (highest for NH4+ and lowest for SiO2) and metal concentration. Underlying mechanisms are combinations of burrow ventilation and bioirrigation with stimulation of element‐specific processes as coupled nitrification–denitrification, co‐precipitation and inhibition of anaerobic paths such as Fe3+ or Mn4+ reduction or re‐oxidation of their end products. The combined activity of benthic algae and chironomid larvae may significantly attenuate internal nutrient recycling in shallow eutrophic ecosystems, and contribute to the control of pelagic primary production.

Macrobenthic communities in water bodies and streams of Svalbard, Norway

ABSTRACTDiversity of macrobenthic communities was studied from water bodies and streams of Spitsbergen, Svalbard archipelago, Norway. In total 162 quantitative samples from different regions of Spitsbergen were analysed in relation to environmental variables. Macrobenthic communities were found on all kinds of substrates (except for the periglacial zone), representing a wide range of biological communities: solid-bottom, soft-bottom, macrophytes and small brook associated. However, taxonomical structure is very simplified, with particular dominance of the Chironomidae family. Chironomid larvae dominated highly in diversity, abundance and biomass. Overall macrobenthic communities were characteristic, with remarkable dominance of one species and general omnipresent taxonomical scarcity (average 2.8 species per sample). In total we found 30 taxa. We distinguished 16 types of macrobenthis communities, with characteristic dominance of different taxa: chironomids (11 types), oligochaete Enchytraeidae family (3), caddisfly Apatania zonella (1) and gammarid amphipod Gammarus setosus (1). Regarding environmental variables, temperature and pH had the most significant influence on the abundance of macrobenthic organisms. It is hypothesized that the structural convergence of different types of communities is their common response to extreme high Arctic living conditions. On the other hand, different chironomids may dominate in the same habitats and water bodies. This gives the effect of lower average similarity of communities and high β-diversity.

The very hungry amphipod: the invasive Dikerogammarus villosus shows high consumption rates for two food sources and independent of predator cues

The invasion of the Ponto–Caspian amphipod Dikerogammarus villosus in European rivers is assumed to reduce macroinvertebrate diversity and to alter ecosystem functions. D. villosus shows an extraordinarily flexible feeding behavior including the ability to use various food sources. On the other hand, its response to predation risk seems to depend on environmental factors. To evaluate the ecological function of D. villosus, we estimated the daily food consumption for different food sources and analyzed potential effects of predator avoidance behavior on feeding. D. villosus consumption of willow leaves or chironomid larvae was quantified in 24-h laboratory experiments with and without kairomones of the European bullhead (Cottus gobio). Consumption rates were estimated based on gut content and gut evacuation rate under semi-natural laboratory conditions enabling the animals to feed over the whole time of the evacuation rate experiment. We observed very high evacuation rates and consequently high consumption rates up to 89% of body weight per day. Consumption rates differed significantly between food sources: D. villosus ingested more leaves than chironomid larvae. In contrast, predator cues did not affect the feeding of D. villosus. This might be explained by its strong refuge affinity and probably benefits its successful invasion. A comparison of the estimated consumption rates with results of an own consumption experiment (and other studies) under more artificial conditions indicated that more natural conditions result in higher consumption rates. Consequently, feeding rates from highly artificial experiments should be used with great caution to assess the ecosystem function of D. villosus.

Pattern of Lateralized Behaviors in a Caudate Amphibian, &lt;i&gt;Ambystoma mexicanum&lt;/i&gt;

Laterality of brain and behavior at the individual and/or group level is a characteristic of all vertebrate classes. The general pattern of left-right asymmetry in vertebrates is so that left-eye/right-hemisphere system is used to detect socially important images, like conspecifics, and also recognize danger, while the right-eye/left-hemisphere system is used to discriminate prey and food items from inedible objects. However, the pattern of motor and visual lateralization in caudate amphibians is poorly investigated to date. Here we present the first evidence of individual and group level motor and visual lateralization in sexually mature and immature larvae of the Mexican axolotl, Ambystoma mexicanum , thus presenting a comprehensive characteristic of the lateralized behavioral pattern in a salamander species. First, we performed four successive tests to assess asymmetry in rapid C-start and measure its characteristics in responses to startle stimuli in sexually immature larvae. We experimentally showed that axolotls exhibited a leftward population bias in each of four C-start tests, of which the bias was significant in the second test and in the pooled data for all four tests. Second, in mature axolotls we have found right-sided individual level asymmetry and, at the group level, a tendency to react more actively to food items (live chironomid larvae) appeared in their right visual hemifield. Third, individual axolotl larvae been placed in the square aquarium with two opposite mat walls and two opposite mirror walls preferred to stay near to mirror walls, rather than near to mat walls. At the group level, this preference increased over three successive tests and reached significance in the third test and in the pooled data. At both individual and group levels axolotls showed statistically significant lateralization, preferring to inspect the mirror walls with their left eyes in all three tests. Overall, the expressed pattern of lateralization in the Mexican axolotl corresponds to the general pattern of lateralization established for other vertebrates including anuran amphibians.

Silver bioaccumulation in chironomid larvae as a potential source for upper trophic levels: a study case from northern Patagonia.

Silver (Ag) is a pollutant of high concern in aquatic ecosystems, considered among the most toxic metallic ions. In lacustrine environments, contaminated sediments are a source of Ag for the food web. Chironomidae (Insecta: Diptera) are the most abundant, diverse, and representative insect groups in aquatic ecosystems. Chironomid larvae are closely associated to benthic substrates and link primary producers and secondary consumers. Given their trophic position and their life habits, these larvae can be considered the entry point for the transference of Ag, from the benthic deposit to the higher trophic levels of the food web. Previous studies in lakes from Nahuel Huapi National Park (Northern Patagonia) showed Ag enrichment over background levels (0.04-0.1μgg-1 dry weight) both in biota (bivalves and fish liver) and sediments from sites near human settlements. The aim of this study was to analyze the role of chironomids in the transference of Ag from the benthic reservoir of Lake Moreno Oeste to the food web. The concentration of Ag in chironomid larvae tissue ranged from 0.1 to 1.5μgg-1 dry weight, reaching a bioaccumulation factor up to 17 over substrates and depending on the associated substrate type, feeding habitats, larval stage, and season. The main Ag transfer to higher trophic levels by chironomids occurs in the littoral zone, mostly from larvae inhabiting submerged vegetation (Myriophyllum quitense) and sediment from vegetated zones. This study presents novel evidence of the doorway role played by chironomid larvae in Ag pathways from the sediments into food webs of freshwater ecosystems.