193 research outputs found
Thoracic horn structure in Orthocladiini pupae (Diptera: Chironomidae: Orthocladiinae)
No full textThe pupal thoracic horn in Chironomidae is a respiratory organ specialized for oxygen adsorption and the horn surface was suggested as a measure of a species’ oxygen requirements. This structure was analyzed in 31 species belonging to the tribe Orthocladiini within the genera
Cricotopus, Eukiefferiella, Orthocladius and Tvetenia. Optima for dissolved oxygen and water temperature were calculated for each
taxon using information from a large database. The species with extensive horn are the most resistant to low oxygen levels and
high temperature, and no significant correlation was detected between horn surface and species optima. The species of the genus
Cricotopus, characterized by reduced thoracic horn, tolerate lower oxygen levels then Orthocladius: it is suggested that higher
tolerance is bound to more frequent respiratory undulations. At taxonomic levels below tribes behavioural and physiological
adaptations more than morphological ones may explain the result
Response of chironomid species (Diptera, Chironomidae) to water temperature: effects on species distribution in specific habitats
No full textThe response of 443 chironomid species to water temperature was analyzed, with the aim of defining their thermal optimum, tolerance limits and thermal habitat. The database included 4442 samples mainly from Italian river catchments collected from the 1950s up to date. Thermal preferences were calculated separately for larval and pupal specimens and for different habitats: high altitude and lowland lakes in the Alpine ecoregion; lowland lakes in the Mediterranean ecoregion; heavily modified water bodies; kryal, krenal, rhithral and potamal in running waters. Optimum response was calculated as mean water temperature, weighted by species abundances; tolerance as weighted standard deviation; skewness and kurtosis as 3rd and 4th moment statistics. The responses were fitted to normal uni- or plurimodal Gaussian models. Cold stenothermal species showed: i) unimodal response, ii) tolerance for a narrow temperature range, iii) optima closed to their minimum temperature values, iv) leptokurtic response. Thermophilous species showed: i) optima at different temperature values, ii) wider tolerance, iii) optima near their maximum temperature values, iv) platikurtic response, often fitting a plurimodal model. As expected, lower optima values and narrower tolerance were obtained for kryal and krenal, than for rhithral, potamal and lakes. Thermal response curves were produced for each species and were discussed according to species distribution (i.e. altitudinal range in running water and water depth in lakes), voltinism and phylogeny. Thermal optimum and tolerance limits and the definition of the thermal habitat of species can help predicting the impact of global warming on freshwater ecosystems
Biomonitoring of lake sediments using benthic macroinvertebrates
No full textThe Water Framework Directive (2000/60/EC) is an innovative piece of legislation aimed at protecting the quality of all continental
and coastal waters in Europe through an ecological evaluation of the ecosystems. Since it is widely acknowledged that the
greater the ecological realism the greater the difficulty of its definition, we describe the different uses of benthic organisms as a
tool for assessing the quality of sediment in lakes. We review the responses from single species to the community. We focus on
studies in the laboratory and in the field, and we also critically consider the use of predictive models for these evaluations.
Our discussion of the information collected underlines the importance of the relation between sensitivity of single species and
contaminants. Moreover, the recent approach in developing mechanistic models to predict the response of natural communities
seems to be particularly powerful for community ecology, and we strongly recommend more effort along these lines
The effects of tricyclazole treatment on aquatic invertebrates in a rice paddy field
No full textThe benthic macroinvertebrate community response to tricyclazole treatments in an experimental rice paddy field was analyzed using univariate and multivariate statistical analysis. The observed community presented low species diversity, dominated by the gastropods Gyraulus albus and Physa fontinalis, the oligochaetes Branchyura sowerbyi and the hirudinea Alboglossiphonia heteroclita.
No significant effect was detected following tricyclazole treatments, while a moderate shift in community composition was observed during the sampling period, with gastropods prevailing at the end of the experiment. Multivariate classification tree analysis emphasized the importance of sampling date over tricyclazole treatments. The limited period of submersion of the rice paddy field, the low oxygen content and the high water temperatures are thought to be the reasons of the low community diversity observed
Chironomid species as indicators of freshwater habitat quality
No full textChironomid species responses to environmental factors were investigated because knowledge of species optima and tolerance is needed to develop an effective method for assessing the ecol. quality of freshwater ecosystem. The focus of the present study was on the optima at the species level for which environmental data are available with the objective of assigning each chironomid species to an appropriate quality class. The database used for the anal. includes samples collected predominantly in northern Italian lakes and running waters since the 1970s. Environmental response was quantified for 315 species with mean and std. deviation of variables weighted for taxa abundance. The 25 species with the most numerous data points available were arranged according to quality class values detd. by variable weighted means. Many species were found in class 1 waters (best water quality) while few species occurred in class 4 and 5 waters. The same species often occurred in waters that indicated poor and good water quality. Nitrate-N was the variable that most often placed species in low quality classes, whereas both dissolved oxygen and PO4-P usually placed species in class 1. Different species of the same genus often have different optima. [on SciFinder (R)
Hydrobaenus olfa Zerguine & Rossaro 2010, n. sp.
No full text<i>Hydrobaenus olfa</i> n. sp. <p>Holotype: 1 pharate ♂, Algeria: Garaet Ank El Djmel, 35° 46.298' N, 6° 52.00' E, 15.I.2004. Paratypes: 1 ♂, 4 pupal exuviae, 4 larvae, as for holotype. Type material deposited in University of Milano, DiPSA Dept., Italy.</p> <p> <b>Etymology:</b> The species is named after Olfa, the name of the son of the first author.</p> <p> <b>Diagnostic characters:</b> The species can be easily separated from all the other known species of <i>Hydrobaenus</i> for the high number of anal macrosetae (6–8) on anal lobes of pupa. The larval and adult male characters emphasize that the species is near to <i>Hydrobaenus pilipes</i> (Malloch, 1915). The male imago has a slender relatively well developed anal point, devoid of setae, gonostylus without an outer corner and a developed crista dorsalis, the larva has an AR about 2, a large bifid yellow median tooth and a narrow small dark first lateral tooth.</p> <p> <b>Male</b> (n = 2). Medium sized species, wing length 3.22 mm.</p> <p> <i>Antenna.</i> With 13 flagellomeres; groove beginning at flagellomere 4; sensilla chaetica on flagellomeres 2– 3 and terminal. Antennal ratio 2.33, ultimate flagellomere 828 µm long.</p> <p> <i>Head.</i> Eye bare, with parallel-sided dorsomedian extension. Temporal setae clearly separated into two groups, with 5 inner verticals reduced in size, 3 larger outer verticals, 2 postorbitals. Cibarial pump with anterior margin concave, narrow anteriorly, broadened posteriorly. Palp normal with 5 segment; palpomeres lengths (µm): 39, 42, 140, 109, 165. Apex of 3rd palpomere with 3 sensilla clavata.</p> <p> <i>Thorax.</i> Antepronotum moderately developed; lobes joined along a broad suture with anterior notch, in broad contact, 7 lateral antepronotals; 8 acrostichals reduced in size, placed in a row, beginning some distance from antepronotum; 11 dorsocentrals arising from a white spot; 10 strong prealars, arising from a white spot; 7 scutellars on two rows. Anterior and posterior anepisternum II and preepisternum without setae.</p> <p> <i>Wing</i> badly preserved in type material. Membrane without setae, with distinct punctation. Anal lobe somewhat reduced. Costa moderately extended; R 2 +3 running and ending midway between R 1 and R 4 +5; R 4 +5 ending distally of M 3; An ending distally of FCu; Cu 1 slightly curved apically. R with setae, R 1 and R 4 +5 without setae. Squama fringed with more than 50 setae arranged in many rows.</p> <p> <i>Legs.</i> Pseudospurs present on ta 1 of mid and hind legs. Sensilla chaetica on tarsomere 1 of hind leg absent. Setae on ta 1 of p 3 c. 140 µm long. Pulvilli absent. LR c. 0.57. Legs measurements in Table 1.</p> <p> <i>Abdomen.</i> Tergites with irregularly scattered setae; T IX with about 20 setae.</p> <p> <i>Hypopygium</i> (Fig. 1). Anal point well developed 40 µm long, transparent, with parallel sides; apex without setae and microtrichia, with numerous setae at base. Phallapodeme and aedeagal lobe well developed. Anterior margin of transverse sternapodeme convex, oral projections pointed, never conspicuously thickened. Virga consisting of 2 well developed spines 30–40 µm long and 2 other slender and lighter spines. Gonocoxite with well developed inferior volsella well separable into a dorsal and a ventral lobe. Dorsal lobe squared, with short setae and microtrichia, ventral lobe developed beyond dorsal lobe. Superior volsella not developed. Gonostylus rounded apically, with a rounded outer corner, without an outer projection; crista dorsalis absent; megaseta 17 µm long.</p> <p> <b>Pupa</b> (n = 5). Medium sized pupae, 6.06 mm long, abdomen 4.85 mm long.</p> <p> <i>Cephalothorax.</i> Frontal apotome rugose; with well developed warts. Frontal setae present on frontal apotome. Antennal sheath above pedicel smooth. Ocular field with 1 postorbital and 1 vertical. Two antepronotals, c. 100 µm long. Thoracic horn c. 500 µm long (Fig. 2), with pointed apex, sparsely covered with strong spinules. Three precorneals present, arranged in a triangle, 180, 100, 80 µm long; 4 dorsocentrals present, dc 2 closer to dc 1 than to dc 3; prealar minute. Thorax weakly rugulose. Wing sheath smooth.</p> <p> <i>Abdomen</i> (Fig. 2). Tergite I without anteromedian shagreen; T II with faint median shagreen; T III–VI with more extensive, stronger shagreen; T VII–IX with faint anteromedian shagreen. Sternites I and IX without anteromedian shagreen; faint anteromedian and posteromedian shagreen present on remaining sternites. Tergite II with posterior hooklets. Pedes spurii A present on sternites IV–VII; pedes spurii B on segment II, well developed. Apophyses dark and well delineated on both tergites and sternites. Segment I with 4–5 D setae, 2–3 L setae and 3 V setae. Segments II–VI each with 5 D setae, 4 L setae, no taeniate setae on segments IV–VI. Segment VII with 4 taeniate L setae; segment VIII with 5 taeniate L setae, 200–250 µm long.</p> <p> <i>Anal lobe</i> (Fig. 2). With 6–8 equally long anal macrosetae placed on well developed tubercles and with full fringe of about 40, 160 µm long, setae, fringe always reaching macrosetae. Apex of anal lobe rugulose, with lines. Male genital sac ending near apex of anal lobe. Genital sheath not ending in papilla but constricted at apex.</p> <p> <b>Larva</b> (n = 4). Medium sized to large larvae, about 9 mm long.</p> <p> <i>Antenna</i> (Fig. 3). With 6 segments, segments consecutively smaller, segment 6 vestigial. Antennal segments lengths (in µm): 76.1, 16.7, 11, 6, 3, 1. Antennal ratio about 2. Ring organ near base of first segment. Blade slightly shorter than flagellum. Lauterborn organs distinct, about as long as third segment.</p> <p> <i>Labrum</i> (Fig. 3). S I coarsely plumose. Labral lamella simple, triangular, very weakly sclerotized. Pecten epipharyngis consisting of 3 simple, sclerotized smooth spines; 7–8 pairs of chaetulae laterales present, all smooth, 2 chaetulae basales present bifid at apex. Premandible with 2 apical teeth and small inner accessory tooth; brush absent.</p> <p> <i>Mandible</i> (Fig. 3). Apical tooth 18 µm long, shorter than combined width of 3 inner teeth (25 µm), with a darkened molar area resembling a 4th tooth. Seta subdentalis apically with a small indentation. Branches of seta interna smooth.</p> <p> <i>Mentum</i> (Fig. 3). With large, bifid median tooth and 6 pairs of lateral teeth. Median tooth 12 µm wide, pale; first lateral teeth 4 µm wide, darker and lower than median tooth; second lateral teeth 8 µm wide; other teeth consecutively smaller. Ventromental plate well developed; beard absent.</p> <p> <i>Maxilla</i> (Fig. 3). Anterior lacinial chaeta apparently neither longitudinally curled, nor forming nearly complete cylinder. No lamella of galea serrated. Pecten galearis not developed.</p> <p> <i>Body.</i> Procercus well developed, sclerotized posteriorly, 50–60 µm high, 30–40 µm wide, dark with 7 apical setae (anal setae). Anal setae 580–600 µm long. Anal tubules not swollen, shorter than posterior parapods. Posterior parapods 357 µm long in one paratype, 227 µm long in the other paratype (3 instar?). Supraanal seta 262–300 µm long in one paratype, 103 µm long in the other paratype.</p> <p> <b>Habitat.</b> The type locality, Garaet Ank El Djmel, is a big pond of about 3.5 ha and a depth of 0.6 m. It belongs to the complex wetlands of the Eastern Hauts plateaux in Algeria. Garaet Ank El Djmel has a sandy bed and is very salty of about 10 mS cm –1. The specimens were collected on 15 January 2004 where the average air of temperature was 5.2°C and the average water temperature was 6.3°C.</p>Published as part of <i>Zerguine, Karima & Rossaro, Bruno, 2010, A new species of Hydrobaenus Fries, 1830 (Diptera, Chironomidae) from Algeria, pp. 37-43 in Zootaxa 2507 (1)</i> on pages 38-41, DOI: 10.11646/zootaxa.2507.1.2, <a href="http://zenodo.org/record/5301923">http://zenodo.org/record/5301923</a>
Strumenti per lo sviluppo di un indice di qualità del macrobenthos per i laghi italiani
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