Seasonal changes in the stable isotope values of lake-dwelling chironomid larvae in relation to feeding and life cycle variability

1. We studied seasonal changes in the carbon and nitrogen stable isotope ratios of larval Chironomus anthracinus and C. plumosus from the profundal sediments of four contrasting lakes. 2. Pronounced seasonal changes in both δ¹³C and δ¹⁵N values were evident in chironomid larvae of both species from two summer‐stratified, eutrophic lakes: Esthwaite Water and Wyresdale Park. Changes were most marked in the larvae of C. plumosus and in larvae from greater depths. In contrast, neither C. anthracinus in summer‐stratified but mesotrophic Schöhsee, nor C. plumosus in polymictic Großer Binnensee, showed marked seasonality in larval stable isotope ratios. 3. The particularly strong ¹³C‐depletion of larvae from the stratified, eutrophic lakes is attributed to a significant contribution of methane‐derived carbon to their diets. Feeding by larvae on isotopically light methanotrophic bacteria appears to occur mainly when autumn overturn of the water column restores oxygenated conditions to the sediment surface. At this time both δ¹³C and δ¹⁵N values of larvae decreased sharply. 4. Changes in the mean stable isotope ratio of the larval populations can also occur when larger, more isotopically light, larvae pupate and emigrate from the population to hatch as imagos. This effect can induce seasonal changes in larval isotope values even in lakes in which there is no evidence of a significant involvement of methane‐derived carbon in their diets. Variations in emergence patterns between species and between lakes may generate differences in the seasonal pattern of change in stable isotope ratios in larval populations. 5. Our results emphasise the importance of adequate seasonal sampling if stable isotope ratios are to be used as biomarkers to study the role of key groups, such as chironomid larvae, in the trophic structure of lakes.     

Feeding efficiencies of Chironomus plumosus (L.) and C. anthracinus Zett. (Diptera: Chironomidae) in mesotrophic Lake Erken

SUMMARY.

• 1 Absorption efficiencies of nitrogen and carbon in two Chironomus species found dominating in the profundal zone of mesotrophic Lake Erken were determined gravimetrically.
• 2 Absorption efficiencies for C. plumosus showed greater seasonal variation than those of C. anthracinus, with low efficiencies coinciding with the summer dominance of flagellate phytoplankton and with high C:N ratios.
• 3 Overall mean absorption efficiencies (±SE) for carbon and nitrogen, respectively, were 26.8% (±1.9) and 29.3% (±1.9) for C. plumosus, 24.6% (±1.7) and 28.1% (±1.8) for C. anthracinus.
• 4 Significant differences were found to exist between the C: N ratios of the superficial 2 cm sediment layers and those of Chironomus anterior midgut contents.
• 5 C. anthracinus appears to be a deposit feeder ingesting particulate matter scraped from the recently deposited surface sediments. The greater seasonal variation found in the absorption efficiencies of C. plumosus, together with the lower C:N ratios, support the contention that this species is a filter feeder with the nutritional quality of ingested matter depending primarily on pelagic inputs.

     

Chironomus species (Diptera: Chironomidae) in the profundal benthos of Spanish reservoirs and lakes: factors affecting distribution patterns

• 1 The taxonomy, distribution and habitat preferences of Chironomus larvae from profundal benthos of reservoirs and natural lakes in Spain are presented. The 114 water bodies studied were medium to large reservoirs and lakes throughout Spain, and were visited on at least two occasions (summer and winter). Out of the natural lakes investigated, Chironomus larvae were found only in one karstic lake (Banyoles), and to date, these have not been found in the high mountain lakes of the Spanish Pyrenees or Sierra Nevada, or in Spain's largest oligotrophic lake (Sanabria).
• 2 Multiple regression with environmental data from reservoirs showed that the density of Chironomus larvae was inversely correlated with water depth, temperature and sulphide content of the bottom water, but positively correlated with alkalinity and particulate organic nitrogen (PON) content of bottom water. Thus, the density of Chironomus larvae was higher in shallow reservoirs from the eastern part of Spain (calcareous water and higher PON), but markedly lower in southern reservoirs (higher temperature and higher sulphide).
• 3 According to morphological and cytological characteristics, three species of this genus have been identified in the samples examined: C. bernensis, C. plumosus and C. nuditarsis. Reasons for the absence of other widespread European species are discussed.
• 4 Using canonical correspondence analysis to relate species and environmental variables, C. bernensis showed a significant preference for reservoirs with higher oxygen concentrations in bottom water and lower total reactive phosphorus (TRP) content at the surface than those reservoirs where C. plumosus‐type were found. This suggests that the smaller C. bernensis prefers mesotrophic reservoirs and the larger C. plumosus‐type (C. plumosus + C. nuditarsis) prefers eutrophic reservoirs. Taking into account the TRP/depth index for those samples collected at depths below the thermocline, and thus, where oxygen can be a limiting factor, C. bernensis and C. nuditarsis were present in reservoirs in which the index was low (< 1:170 for C. bernensis and >1:800 for C. nuditarsis), while C. plumosus thrived in reservoirs with higher index values (<1:20). These differences may reflect the preference of C. bernensis and C. nuditarsis for detrital material, while C. plumosus prefers phytoplankton. These observations are in agreement with the depth distribution of each species: C. plumosus was restricted to reservoirs less than 46 m deep, whereas the other two species (i.e. C. bernensis and C. nuditarsis) were found up to depths of 65 and 80 m, respectively.
• 5 Data from a transect (5–20 m deep) in Lake Banyoles are consistent with the general pattern described in reservoirs. In this lake, a high density of C. bernensis was recorded from littoral and sublittoral areas with abundant oxygen (above or close to the thermocline), whereas C. plumosus was scarce in several parts of the lake, especially in oxygen‐deficient areas during the summer. This karstic, oligotrophic lake has a low TRP/depth index, and therefore, we expected C. bernensis to be dominant in the littoral, as is the case. Nevertheless, the severe depletion of oxygen caused by meromixis, and the high hydrogen sulphide concentration benefit C. plumosus in deeper zones. Chironomus nuditarsis was scarce in Lake Banyoles and only found at considerable depths.

     

Differences in feeding behaviour among Chironomus species revealed by measurements of sulphur stable isotopes and cadmium in larvae

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Emergence of chironomidae from Findley Lake in the coniferous forest of the cascade mountains after early and late thaws

Chironomidae were collected in floating emergence traps on 27.5 m deep Findley Lake in the coniferous forest of the Cascade Mountains, USA, from 1972 to 1975. There was considerable yearly variation in the date of thaw, the total number of Chironomidae that emerged and the relative abundance of each species. In 1972, 1973 and 1975 when there were early thaws, Tanytarsus and Procladius were the most common Chironomidae. Many of the common species started to emerge before the lake had completely thawed. In 1973 when most of the lake thawed June 7 and the surface water reached a maximum temperature of 19.25 °C in July, the Tanytarsus chinyensis group, Stictochironomus and Chironomus started to emerge from deep water when there was still ice along shore. Procladius nr gretis and Orthocladius started to emerge two days after the last ice had melted. In 1974 when most of the lake did not thaw until July 30–31, the surface water reached a maximum temperature of only 12.5 °C in August. Only a fifth as many Chironomidae emerged as in 1973. Most of these were Procladius and Orthocladius which had their maximum emergence when most of the lake was still frozen. The emergence of each species was reduced except Orthocladius. Procladius contributed the greatest biomass that emerged each year, but the second greatest biomass was contributed by different genera each year.     

On the structure and function of the ventral tubuli of some Chironomus larvae (Diptera,Nematocera)

The ultrastructure of the walls of the tubuli of larvae of two Chironomus species living in lakes and four species from small ponds were studied, in order to decide whether the function of the tubuli is primarily a respiratory one or not.Data suggest a reinforcement of the concept of a respiratory function and a hypothesis is discussed which might explain the differences found between the tubuli of lake- and pond-dwelling species.     

Comparison of Chironomus usenicus and Chironomus curabilis with species of the group plumosus (Diptera) inferred from the mitochondrial DNA Gene COI and by the polytene chromosomes banding pattern

The sequence of a 595-bp fragment of the mitochondrial COI gene was determined for the species Chironomus usenicus and Chironomus curabilis of the genus Chironomus. Phylogenetic reconstructions based on the analysis of the COI gene sequence coincide on the whole with cytogenetic data, permitting Ch. usenicus and Ch. curabilis to be regarded as members of the group plumosus. Chironomus usenicus and Ch. plumosus have identical COI gene sequences. Two hypotheses explaining this identity are considered: inheritance of mtDNA from one of the parental species during hybridogenesis and horizontal transfer of mitochondrial genes.     

Distribution of chironomids (Diptera) in low arctic West Greenland lakes: trophic conditions, temperature and environmental reconstruction

1. Surface sediment samples of subfossil chironomid head capsules from 47 lakes in southern West Greenland were analysed using multivariate numerical methods in order to explore the relationship between chironomid assemblages and selected environmental variables. The study lakes are located along a climate gradient ranging from coastal maritime conditions near the Davis Strait to a continental climate near the margin of the Greenland ice sheet. 2. High‐resolution surface water temperatures were measured through the summer season using automatic data loggers in 21 of the study lakes. The mean July surface water temperature (1999) ranged from 7.3 to 16.5 °C in the data set. 3. In all lakes, a total of 24 chironomid taxa were recorded; Micropsectra, Psectrocladius, Chironomus and Procladius were the dominant genera. There was a strong correlation between the trophic variables [total nitrogen and total phosphorus (TN, TP)] and temperature, and in redundancy analysis (RDA) the three variables explained almost equal significant amounts of variation in the chironomid data (19.8–22.3%). However, temperature lost significant explanatory power when the effect of TN was partialled out in RDA. 4. The lakes were classified using two‐way indicator species analysis (TWINSPAN ) into eight groups defined by temperature, trophic variables, salinity (conductivity) and lake‐morphometric data. Fourteen chironomid taxa showed significant differences in percentage abundances among groups, with Heterotrissocladius, Micropsectra, Ablabesmyia and Chironomus as the most robust group‐indicator taxa. Forward selection of taxa in multiple discriminant analysis was used to fit chironomid assemblages into lake groups. Using only eight taxa, 95% of lakes were correctly classified at a second TWINSPAN division level (four groups) and 85% of lakes at a third division level (eight groups). 5. This study showed that there is considerable potential in using subfossil chironomid head capsules as paleoenvironmental indicators in both short‐ and long‐term (down‐core) studies of lake ontogeny and palaeoclimate conditions in West Greenland. However, because of the strong correlation between temperature and trophic variables, a quantitative reconstruction of lake‐ and habitat‐type is recommended, in combination with direct reconstruction of single variables such as temperature.     

The chironomid fauna of four shallow,humic lakes and their representation by subfossil assemblages in the surficial sediments

A comparison of the present chironomid fauna of four shallow, humic lakes with the subfossils of surficial sediments is made. The chemistry and benthos of the lakes investigated varied greatly. Results indicate a reasonable correlation between biocenoses and thanatocenoses, but a marked under-representation ofProcladius is apparent. It is suggested that, at least in shallow, humic lakes,Procladius be excluded in attempts to reconstruct chironomid communities from subfossils.     

Carbon pathways to zooplankton: insights from the combined use of stable isotope and fatty acid biomarkers

1. Numerous studies have quantified the relative contribution of terrestrial‐ and phytoplankton‐derived carbon sources to zooplankton secondary production in lakes. However, few investigated the pathways along which allochthonous and autochthonous carbon (C) was actually conveyed to consumers. 2. We suggest that the combined use of fatty acid and stable isotope biomarkers could solve this issue. We conducted a field study on two oligotrophic lakes, in which primary production increased significantly between 2002 and 2004. We used modelling to estimate the contribution of terrestrial‐ and phytoplankton‐derived C to particulate organic C (POC) and zooplankton production from their δ¹³C values in 2002 and 2004. 3. According to the isotope model, phytoplankton‐derived C accounted for a major part of the POC pool in both lakes and supported more Daphnia sp. production in 2004 than in 2002. Fatty acid data revealed that increased contribution of algal‐C to Daphnia production, although common between both lakes, was achieved through C pathways that were different. In one lake, Daphnia grazed more intensively on phytoplankton, whereas in the other there was greater grazing on bacteria. In the latter case, the increased primary production resulted in greater release of algal‐derived dissolved organic C (DOC), which may have supported extra bacterial and eventually Daphnia, production. 4. This is the first study illustrating that the combination of fatty acid and stable isotope biomarkers could further our understanding of the factors controlling the relative magnitude of food webs pathways conveying organic matter to zooplankton.     

The phenology ofProcladius crassinervis (Zett),Procladius signatus (Zett) andProcladius choreus (Mg) (Diptera,Chironomidae) at Lake Hald,Denmark

In an investigation of the phenology of the chironomid species of Lake Hald, Denmark, a very late flight activity (September–November) of the univoltine speciesProcladius choreus (Mg.) was observed. Among observations of the phenological patterns of univoltine chironomids inhabiting lakes of the Baltic type in Denmark, the phenological pattern ofProcladius choreus stands alone (JÓNSSON, 1987; LARSEN, 1991). Further two species of the genusProcladius Skuse,viz. Procladius crassinervis (Zett) andProcladius signatus (Zett), were found in the investigation and the phenological pattern of the three congeneric species was clearly allochronic, withProcladius crassinervis flying in spring,Procladius signatus flying in summer andProcladius choreus flying in autumn.     

Deformities in larval Procladius spp. and dominant Chironomini from the St. Clair River

The benthic community of the St. Clair River is impacted by the petrochemical complex near Sarnia, Ontario. Larvae of the common chironomid Procladius spp. and dominant Chironomini from various sections of the river were examined to determine if the incidence of morphological deformities in their mouth parts reflected the degree of chemical pollution. Procladius had a much greater (14%) incidence of deformed ligula downstream of the industrial section near Sarnia, than occurred in Lake St. Clair (3%), or at the mouth of Bear Creek, which drains agricultural land east of the St. Clair delta (7%). The incidence of deformed ligula at a control site in Lake Superior was 4 percent. The incidence of deformities in Procladius larvae was lower than that in Chironomus larvae from the same site, but greater than that in other chironomid genera.     

Homology of Balbiani rings among chironomid species and localization of a new mobile element on the polytene chromosomes

The results ofin situ cross-hybridization of the cloned DNA fragments of BRa, BRb and BRc fromChironomus thummi to the polytene chromosomes of 14Chironomus species andCamptochironomus tentans are presented. BRs of the species studied were demonstrated to contain the homologus DNA sequences. The cloned fragment from the BRa ofC. thummi hybridized with the BRa ofC. piger and with a region on the arm G ofC. tentans andC. plumosus, the latter species had no extra BR. The clone 16 from the BRb ofC. thummi hybridized only with the developed BR on the arm G of all species studied. The sequence from the BRc ofC. thummi was located in the BRc ofC. piger and in the developed BR ofC. plumosus andC. nuditarsis, which were located at the most distal end of arm G. These clones can be used as markers of homologous BRs. The new mobile elements C6.10 fromC. thummi genome were localized on the polytene chromosomes of 10Chironomus species andCamptochironomus tentans. The species of the generaLipiniella, Cryptochironomus andGlyptotendipes did not contain the sequences homologous to ME C6.10.     

Ammonium excretion by some freshwater zoobenthos from a eutrophic lake

Relationships between the ammonium excretion rate of zoobenthos and temperature were examined for two chironomids, Chironomus, plumosus and Tokunagayusurika akamusi, one chaoborid, Chaoborus flavicans, and two tubificids, Limnodrilus spp. and Branchiura sowerbyi, which often dominate in eutrophic lakes. The representative Q₁₀ value and excretion rate at 15° C for each species were as follows: C. plumosus, 1.67, 1.40, (µg N mg dry w.^–1 d^–1 ); T. akamusi, 1.02 (< 15° C), 0.33; C. flavicans, 1.49, 2.87; Limnodrilus spp., 2.98, 0.59; and B. sowerbyi, 3.15, 0.79.     

The hemoglobin concentration ofChironomus cf.Plumosus l. (Diptera: Chironomidae) larvae from two lentic habitats

Hemoglobin concentrations ofChironomus cf.plumosus larvae were measured in two different habitats of the same pond. Larger larvae have higher hemoglobin concentrations than small larvae. There is strong indication that the animals of poorly oxygenated deep water, have higher hemoglobin concentrations than the animals from the well-oxygenated littoral zone.     

Effect of temperature on fatty acid composition and development of unfed Siberian sturgeon (A. baerii) larvae

The fatty acid metabolism in fish is influenced by various factors, including fish species, water temperature, water environment and diet supply. The aim of present work is to investigate the fatty acid composition of yolk‐stage Siberian sturgeon larvae reared at three different temperatures. Fertilized Siberian sturgeon eggs were transferred to the Lodi Aquaculture Research Center of the University of Milan, divided in three aquaria, each containing three incubators and incubated at 16°C. After hatching the temperature was switched to 16, 19 and 22°C. Larvae sampling was performed at the end of yolk sac reabsorption. No feed was dispensed during the trial. Eggs and larvae were weighed and fatty acid profile was determined by GC‐FID analysis after lipid extraction by chloroform/methanol mixture and fatty acid transesterification by methanolic hydrogen chloride. The fertilized eggs had a weight of 23.27 mg and a lipid content of 2.67 mg/egg. At hatching, the weight was 12.2 (0.17 SD) mg and lipid content 1.9 (0.6 SD) mg/larva. At the end of the trial, larvae mean weight was 33.6 (3.6 SD), 34.7 (1.8 SD) and 36.9 (1.1 SD) mg, while lipid content was 2.0 (0.3 SD), 2.1 (0.3 SD) and 2.0 (0.2 SD) mg for larvae reared at 16, 19 and 22°C respectively, without statistically significant difference. Larvae subjected to the highest water temperature showed a faster yolk‐sac absorption. No differences were found across temperatures regarding survival rates and regarding ontogenic development. The fatty acid composition of larvae was affected by the temperature. Larvae reared at 16°C had the lowest amount of saturated fatty acids, mainly due to a lower palmitic acid content, that was offset by a higher level of linolenic and linoleic acid, if compared with larvae reared at 19°C and 22°C. The study suggests that at a lower temperature sturgeon spare unsaturated fatty acid consuming preferably saturated fatty acids, increasing our knowledge of the fatty acid metabolism in this species.     

On the Possibility of Hybridogenesis in the Origin of Midge Chironomus usenicus Loginova et Beljanina (Chironomidae,Diptera)

Hybridogenesis as a possible way of speciation in Chironomidae was considered with special reference to the species Chironomus usenicus resulting from hybridization between C. plumosus and C. behningi. The three species had 2n = 8 and belonged to the thummi cytocomplex with chromosome arm combinations AB, CD, EF, and G. Arm G had a marker chromosome disk sequence (CDS) and was used to demonstrate the hybrid origin of C. usenicus. Most C. usenicus larvae were heterozygous in CDS of arm G. CDS use G2 proved to be identical to CDS beh G1 ofC. behningiand CDS use G1, to CDS plu G1 of C. plumosus. It was assumed that C. usenicus results from hybridization between eurybiont C. plumosus and stenobiont C. behnigni at the boundary of their species areas, in freshwater or brackish water bodies of the southern Saratov oblast and northern Kazakhstan. Morphologically and karyotypically, the hybrid was probably similar to C. plumosus. Crosses with C. plumosus eliminated virtually all C. behningi chromosome sequences from the karyotype of the hybrid. Further chromosome divergence resulting in C. usenicus involved a number of chromosome rearrangements, including duplication of pericentric heterochromatin and other chromosome regions; inversion, which occurred in arm F (regions 13–16) and was fixed in the karyotype; and other paracentric inversions and deletions accumulated in heterozygote in the karyotype pool of the species. Since C. behningi was eliminated from the introgression zone and its species area reduced, the assimilation character was assumed for introgressive hybridization of C. behningi and C. plumosus.     

Survival and energy metabolism in an oxygen deficient environment. Field and laboratory studies on the bottom fauna from the profundal zone of Lake Esrom,Denmark

The three macroinvertebrate taxa, Potamothrix hammoniensis, Chironomus anthracinus and Pisidium spp. are permanent inhabitants of the regularly microxic/anoxic profundal zone in Lake Esrom. In situ and laboratory studies (10 °C) of metabolism (aerobic and anaerobic) and anaerobic survival in P. hammoniensis and Pisidium spp. are compared with previous results from C. anthracinus. The late summer microxic conditions in the lake lasts 2–2 months, during which the three taxa display metabolic and behavioral strategies in order to survive. All three are respiratory oxy-regulators with critical oxygen levels at 1 mg O₂ l^–1 (P. hammoniensis and Pisidium spp.) or 2–3 mg O₂ l^–1 (C. anthracinus). The lethal time (LD₅₀) in experimental anoxia follows a similar trend, with 150–170 days of survival in P. hammoniensis and Pisidium spp., compared to 2–5 weeks in C. anthracinus. The glycogen stores are almost (C. anthracinus) or fully exploited (P. hammoniensis and Pisidium spp.) during anaerobis and the animals finally enter a state of quiescence or dormancy. During the late phase of anoxia, their metabolism is down at (C. anthracinus) or below (P. hammoniensis and Pisidium spp.) 1% of normoxic metabolism. The populations in the lake behave rather similar in so far that the energy gain from anaerobic degradation of glycogen maximizes 1% of normoxic conditions regardless of species. Also, in Pisidium this appears to be the only energy source during dormancy. However, as previously presented in case of C. anthracinus, P. hammoniensis maintain a partly aerobic metabolism constituting 44% of normoxia during the microxic period, compared to the 12–19% obtained by C. anthracinus. It is thus demonstrated that P. hammoniensis and Pisidium spp. possess a remarkable ability to survive in situ severe oxygen depletion. P. hammoniensis can benefit from the presence of merely traces of oxygen, whereas C. anthracinus with poorer anaerobic survival is strongly dependent on minute oxygen supplies.     

Composition and distribution of sibling species of <Emphasis Type="Italic">Chironomus</Emphasis> Meigen, 1803 (Diptera,Chironomidae) in Curonian Lagoon of the Baltic Sea

The species composition of Chironomus in the Curonian Lagoon has been investigated. It was shown that three sibling species of the plumosus group, namely, Ch. plumosus, Ch. balatonicus, and Ch. muratensis, and a first-generation interspecific hybrid Ch. muratensis × Ch. plumosus lived here. The occurrence frequency in the lagoon was 87, 19, 6, and 3% for Ch. plumosus, Ch. balatonicus, Ch. muratensis × Ch. plumosus, and Ch. muratensis, respectively. The species Ch. plumosus was recorded in all the areas (southern, central, and northern), while Ch. balatonicus was found only in the northern area in the village of Juodkrante near the city of Klaipeda. Presumably, the distribution of these sibling species is due to the presence of a salinity gradient in the lagoon.     

C-banding in the polytene chromosomes of species of the plumosus group (Diptera,Chironomidae) and their experimental hybrids

The localization and amount of heterochromatin in the plumosus group were studied, including the species Chironomus plumosus L., C. vancouveri and C. balatonicus. The appearance of C bands of Chironomus plumosus in several European populations is traced. The role of the C heterochromatin in the differentiation of this species is discussed. From the evolutionary point of view the Swiss populations, in which large centromere heterochromatin blocks have been discovered, are more varied as to the amount of heterochromatin. The importance of duplications for this process is pointed out. The chromosomes of the individuals from C. vancouveri and C. balatonicus have centromeric, telomeric and interstitial heterochromatin. The centromeric heterochromatin is represented by thin C-bands. The particularities in the appearance of C heterochromatin in C. vancouveri and C. balatonicus reflect the structural peculiarities of their chromosomes. The change in the euchromatin regions in these forms is discussed in the light of transformation of euchromatin to heterochromatin in the process of evolution.The appearance of heterochromatin in hybrids (between populations and between species) created experimentally is traced. A change has been discovered in the appearance of heterochromatin in the hybrids compared to the initial parent forms. This difference is expressed more strongly in inter-species hybrids than in interpopulation hybrids of C. plumosus.