Carabid beetles and chironomid midges are two dominant cold-adapted taxa, respectively on glacier forefiel terrains and in glacial-stream rivers. Although their sensitivity to high altitude climate ...warming is well known, no studies compare the species assemblages exhibited in glacial systems. Our study compares diversity and distributional patterns of carabids and chironomids in the foreland of the receding Amola glacier in central-eastern Italian Alps. Carabids were sampled by pitfall traps; chironomids by kick sampling in sites located at the same distance from the glacier as the terrestrial ones. The distance from the glacier front was considered as a proxy for time since deglaciation since these variables are positively correlated. We tested if the distance from the glacier front affects: i) the species richness; ii) taxonomic diversity; and iii) species turnover. Carabid species richness and taxonomic diversity increased positively from recently deglaciated sites (those c. 160 m from the glacier front) to sites deglaciated more than 160yrs ago (those located >1300 m from glacier front). Species distributions along the glacier foreland were characterized by mutually exclusive species. Conversely, no pattern in chironomid species richness and turnover was observed. Interestingly, taxonomic diversity increased significantly: closely related species were found near the glacier front, while the most taxonomically diverse species assemblages were found distant from the glacier front. Increasing glacial retreat differently affect epigeic and aquatic insect taxa: carabids respond faster to glacier retreat than do chironomids, at least in species richness and species turnover patterns.
At high latitudes and altitudes, ice formation is a major variable affecting survival of freshwater fauna and hence the abundance and composition of invertebrate communities. Freezing, but also ...desiccation and anoxia, are lethal threats to all life stages of aquatic insects, from the eggs to the adults. During cold periods, the aquatic stages commonly remain in or move to a portion of the water body that will not freeze or dry (e.g., deep waters of lakes, springs and hyporheic zone) where they can remain active. Less frequently they migrate to habitats that will freeze at the onset of winter. Insects have developed a complex of strategies to survive at their physiological temperature minimum, comprising (a) morphological (melanism, reduction in size, hairiness/pubescence, brachyptery and aptery), (b) behavioural (basking in the sun, changes in feeding and mating habit, parthenogenesis, polyploidy, ovoviviparity, habitat selection and cocoon building), (c) ecological (extension of development to several years by quiescence or diapause and reduction of the number of generations per year), (d) physiological and biochemical (freezing tolerance and freezing avoidance) adaptations. Most species develop a combination of these survival strategies that can be different in the aquatic and terrestrial phase. Freezing avoidance and freezing tolerance may be accompanied by diapause. Both cold hardiness and diapause manifest during the unfavourable season and: (i) involve storage of food resources (commonly glycogen and lipids); (ii) are under hormonal control (ecdysone and juvenile hormone); (iii) involve a depression or suppression of the oxidative metabolism with mitochondrial degradation. However, where the growing season is reduced to a few weeks, insects may develop cold hardiness without entering diapause, maintaining in the haemolymph a high concentration of Thermal Hysteris Proteins (THPs) for the entire year and a slow but continuous growth. A synthesis of literature regarding adaptation strategies in aquatic insects is presented, highlighting the scarcity of information on freshwater insects from Alpine regions. Most references are on Diptera Chironomidae from North America and North Europe. Some recent findings on aquatic insects from Italian Alpine streams are also presented.
This special issue provides an overview of recent advances in the study of chironomids (Diptera chironomidae), as an outcome of the 20th International Symposium on Chironomidae held in Trento ...(Italy), in July 2017. it includes 27 selected papers, representative of the six topics of the symposium: genetics and cytogenetics, taxonomy and systematics, autecology and physiology, toxicology and adaptive biology, ecology and biomonitoring, palaeolimnology. Most papers emphasise the value of chironomids in the monitoring programmes, mainly on Europe and case histories from South America and Africa. however, as our title indicates, the reported contemporary studies represent a range from the genetic through the autecological to the ecosystem scale. the aim of the volume is to give new insights on ecology and biology of non-biting midges, the freshwater insect family that comprises the highest number of species in the world, in both lentic and lotic habitats.
Acute toxicity and genotoxic activity of 11 pollutants were investigated in wild populations of Diamesa cinerella and Diamesa zernyi (Diptera Chironomidae) from two alpine streams (Italian Alps). D. ...cinerella was collected in two sites on the non-glacial Vermigliana stream, 50 m-upstream and 5-m downstream of the Wastewater Treatment Plant (WTP) at the Tonal Pass (1799 m a.s.l.). D. zernyi was collected in the Presena glacial stream, close to the glacier snout (2685 m a.s.l.). IV-instar larvae were exposed for 24-96 h to increasing concentrations of three drugs (ibuprofen-IBU, furosemide-FUR, trimethoprim-TMP), three personal care products (triclocarban-TCC, tonalid-TON, sucralose-SUCR), and five pesticides (boscalid-BOS, captan-CAP, chlorpyrifos-CPS, metolachlor-MET, terbuthylazine-TER). The experimental concentrations were from one to several million times higher than the highest environmental concentration (EC) measured in the study sites. Two mixtures of pesticides were also prepared: MIX 1K =103 x EC of CPS, MET and TER, and MIX 10K = 104 x EC of CPS, MET and TER. Species- and site-specific responses were observed for both tests. On the basis of survival data, both species resulted very resistant to pharmaceuticals (mainly to FUR for which no effects on survival and movement or pupation were observed), and more sensitive to pesticides (mainly to CPS, MET and CAP). Genotoxicity tests (Comet assay) highlighted a WTP effect under natural conditions and a genotoxic effect for 9 of the 11 tested compounds. Overall, a clear gradient of increasing resistance in larvae from the least (PR0) to the most polluted (TP_dw) site was highlighted by both tests, ecotoxicological and of genotoxicity, as also expected according to species autecology (D. zernyi is restricted to very cold and pristine habitats). D. cinerella living downstream of the effluent accumulates a significantly higher DNA damage than the other populations, highlighting a basal physiological stress condition in nature. It is plausible that these larvae possess chemical resistance strategies to survive already under natural conditions. Diamesa spp. exhibited a higher toxic resistance than any other model species tested to date under the same pollutants, probably associable to its strong cold resistance. The results emphasised that the measured concentrations of Contaminants of Emerging Concern (CECs) and pesticides seem to be far below those required to cause acute effects. However, the effects on freshwater communities of prolonged exposure to mixture of trace CECs and pesticides remain unknown.
Diversity and distribution of chironomid fauna (Diptera: Chironomidae) in 36 springs in the Italian Prealps (Veneto and Trentino NE-Italy, 46°N, 10-11°E) was studied in relation to altitude, spring ...type and grade of disturbance. The springs were located between 62 and 1710 m asl of altitude, in three calcareous mountain areas (Mt. Baldo, Mts. Lessini and Mt. Pasubio). They differed in conservation status (natural, moderately and highly disturbed) and belonged to five hydromorphological types (rheocrene, limnocrene, rheohelocrene, rheolimnocrene, rheohygropetric). Each spring was surveyed once, between early summer and autumn, within 50 m of the spring’s source (eucrenal). A total of 4198 chironomid larvae and pupae were sorted from 111 macroinvertebrate samples collected, belonging to five subfamilies (Tanypodinae, Diamesinae, Prodiamesinae, Orthocladiinae and Chironominae), 41 genera and 60 species/groups of species, and three juveniles taxa. As expected, Orthocladiinae accounted for a large part of specimens (88%) and species (74%), with Tvetenia calvescens/bavarica as the most frequent and abundant taxon, shared by pristine and disturbed springs and by all spring types. Most taxa were found in few sites, and frequencies declined gradually for most wider distributed species. A high number (74%) of rare (= present in less than 10% of sites) taxa were found and from one to 23 taxa were identified per spring. Maximum richness occurred in moderately disturbed (Shannon-H = 1.29±0.60) springs, located at medium-high altitude (385-1266 m asl), according to the intermediate disturbance hypothesis. Even the evenness (Equitability-J) was higher as average in these springs. A Cluster Analysis run on Bray-Curtis similarity index highlighted a high similarity i) between the chironomid assemblages of moderately disturbed and natural springs (44 species in each spring group, with 29 species in common), and ii) between rheocrene and rheohelocrene types, thus the springs with the highest microhabitat heterogeneity. High individuality of springs was revealed, and new information about non-biting midges autecology provided. The utility of chironomids as bioindicators of water quality and ecological state of springs was confirmed, with some species e associated with high disturbance level (e.g., Polypedilum nubeculosum gr. to water intake works) and others with pristine conditions (e.g., Pseudodiamesa branickii).
Recently, the use of Daphnia magna has been proposed in on-line and real-time biomonitoring programmes as an early warning system for evaluating the effluent quality of sewage treatment plants ...(STPs). These systems are based on recording behavioural changes in the test organism resulting from the stress caused by the effluents. Indeed, altered behavioural signals could be induced at sublethal concentrations that are significantly lower than the corresponding EC50. However, at present, it is unknown whether the sensitivity of D. magna can be representative of that of other aquatic organisms, particularly benthic macroinvertebrates. An experiment was designed to verify whether D. magna can be employed in biomonitoring programmes for STPs located in alpine areas as a surrogate for cold freshwater best-adapted species. The responses of survival and behaviour alteration to exposure to the effluent of the Tonale Pass plant (Trentino, Italian Alps, 46°N, 10°E; 1799 m a.s.l.) were compared in a laboratory population of D. magna and a wild population of the chironomid Diamesa cinerella. These larvae were collected from the Vermigliana stream 50 metres upstream of the effluent input. Both organisms were exposed for 24 and 48 hrs to the effluent as it is and to three dilutions (/10, /100, /1000). The mortality rate and behavioural responses (using video tracking systems) were recorded. No significant mortality or change in behaviour was observed in the two species when exposed to the undiluted effluent. Exposure to serial dilutions of the treated effluent did not affect the survival of either species but notably altered their behaviour at both exposure times (e.g., the time spent in activity in D. magna and the average speed of movement and the cumulative distance travelled in both), especially when exposed to the ten-times-diluted effluent. Overall, the findings of this study emphasize that even though D. magna and D. cinerella use different behavioural strategies to cope with adverse environmental conditions, their overall sensitivity to treated effluents is similar. Accordingly, the use of D. magna in biological early warning systems protocols seems to also be sufficiently protective for local, cold-adapted species of alpine freshwater ecosystems.
The metabolic effects of low oxygen content on alcohol-dehydrogenase (ADH) activity and hemoglobin (Hb) concentration were investigated in IV-instar larvae of Chironomus riparius (Diptera: ...Chironomidae) from an Italian stream. Two series of short-term (48 h) experiments were carried out: exposure to (1) progressive hypoxia (95 to 5% of oxygen saturation) and (2) anoxia (at <5% of oxygen saturation). In (1), Hb amount increased with increasing oxygen depletion up to a critical value of oxygenation (about 70% of oxygen saturation). Below this percentage, the Hb amount declined to values comparable with those present in the control. The respiration rate (R) remained almost constant at oxygen saturation >50% and decreased significantly only after 48 h of treatment (= <5% of oxygen saturation) reaching values <100 mmolO2 gAFDW-1 h-1. ADH activity showed two phases of growth, within the first 14 h and over 18 h of exposure. Overall, we inferred that i) Hb might function as short-term oxygen storage, enabling animals to delay the on-set of anaerobiosis; and ii) alcoholic fermentation co-occurs for a short time with aerobic respiration, becoming the prevalent metabolic pathway below 5% of oxygen saturation (<1 mg L-1). These considerations were supported also by results from anoxia exposure (2). In such condition, larvae were visibly stressed, becoming immobile after few minutes of incubation, and ADH reached higher values than in the hypoxia treatment (2.03±0.15 UADH mg prot-1). Overall, this study showed a shift from aerobic to anaerobic activity in C. riparius larvae exposed to poorly oxygenated water with an associated alteration of ADH activity and the Hb amount. Such metabolites might be valid candidate biomarkers for the environmental monitoring of running waters.
1. The longitudinal distribution of macroinvertebrates was investigated in June, August and September 1996 and 1997 in the Conca glacial stream and its tributary (Italian Alps; 46°N, 10°E). The ...principal aim was to test the Milner & Petts (1994) model that predicts the succession of faunal groups downstream of the glacial snout in relation to water temperature and channel stability. The effect of a non‐glacial tributary on the taxonomic richness and density patterns occurring in the glacial stream was also considered.
2. Channel stability showed an atypical longitudinal trend in the Conca glacial stream, being high in the upper part with Pfankuch Index values between 30 and 33. Water temperature exceeded 6 °C at all stations, with average values below 2 °C occurring only within 700 m from the glacial snout.
3. Taxonomic richness and diversity increased downstream. Taxonomic richness in the glacial stream (at about 1.5 km from the glacier) was comparable with the tributary and the reach after the confluence. Abundance also increased downstream in the glacial stream, but not as greatly as the number of taxa.
4. At higher taxonomic levels, the community structure in the tributary stations appeared to be similar to the two stations in the glacial stream just upstream of the confluence. The effect of the tributary was evident mainly at the genus or species level of the Chironomidae community. Some taxa found in the non‐glacial stream (e.g. Cricotopus fuscus, Eukiefferiella coerulescens, Metriocnemus sp., Paratrichocladius rufiventris, P. skirwitensis, Rheocricotopus effusus and Smittia sp.) were found also in the Conca stream but only after the confluence.
5. The upper glacial reach (within 700 m from the glacier snout) was dominated by the chironomid Diamesa spp. Less than 400 m from the glacier other Diamesinae (Pseudokiefferiella parva) and a few Orthocladiinae, especially Orthocladius (Euorthocladius) rivicola gr., colonized the stream. Some Diamesinae maintained relatively dense populations at mean water temperature around 5 °C, while some Orthocladiinae colonized reaches with mean water temperature <3 °C.
6. Contrary to the Milner & Petts (1994) model, Dipteran families such as Empididae and Limoniidae were more abundant in the upper stations than Simuliidae; non‐insects such as Nematoda and Oligochaeta were also numerous at some sites. Leuctridae, Taeniopterygidae and Nemouridae were the first Plecoptera to appear upstream, while Chloroperlidae were restricted to the lower reaches. Among Ephemeroptera, Heptageniidae were more abundant than Baetidae in the glacial sites.
7. In this glacial system channel stability and maximum temperature did not show the expected longitudinal trend and thus a typical kryal community was confined within 700 m from the glacier snout where summer mean water temperature was below 4 °C.
The distribution of 19 macroinvertebrate taxa was related to 36 environmental variables in 3 Alpine glacial streams. Principal component analysis (PCA) and a self-organising map (SOM) were used to ...ordinate sample sites according to community composition. Multiple linear regression (MLR) was carried out with the environmental variables as predictors and each macroinvertebrate taxon as criterion variable, a multilayer perceptron (MLP) used the environmental variables as input neurons and each taxon as output neuron. The contribution of each environmental variable to macroinvertebrate response was quantified examining MLR regression coefficients and compared with partial derivative (Pad) and connection weights approach (CW) methods. PCA and SOM emphasized a difference between glacial (kryal) and non-glacial (krenal and rhithral) stations. Canonical correlation analysis (CANCOR) confirmed this separation, outlining the environmental variables (altitude, distance from source and water temperature) which contributed most with macroinvertebrates to site ordination. SOM clustered kryal, rhithral and krenal in three well separated group of sites. MLR and MLP detected the best predictors of macroinvertebrate response. Pad sensitivity analysis and CW method emphasized the importance of water chemistry and substrate in determining the response of taxa, the importance of substrate was overlooked by linear multivariate analysis (MLR).
The effects of temperature and oxygen saturation on the respiration rate of two cold stenothermal chironomids,
Diamesa insignipes and
Pseudodiamesa branickii were investigated. Fourth instar larvae ...were collected in winter in a glacio-rhithral stream (1300
m a.s.l., Alps, NE-Italy) and their respiration rate was measured with a Clark's electrode in the range 0–14
°C. The respiration rate was significantly higher in
D. insignipes than in
P. branickii at low temperatures (≤4
°C), higher in
P. branickii between 8 and 12
°C and comparable at 14
°C. Higher values of
R (regulation value),
R
25% (respiration rate at 25% oxygen saturation) and
b
1/
b
2 (slope ratio in piecewise linear regression), and lower values of
P
c (critical pressure) and
I (initial decrease) were recorded in
P. branickii than in
D. insignipes. These values are compatible with oxy-regulatory behaviour in
P. branickii, whereas
D. insignipes appeared to be almost an oxy-conformer. On the basis of this autoecological information, new implications regarding survival of species from cold, high altitude habitats under changing climatic conditions are made.
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