Manipulation of habitat quality: effects on chironomid life history traits

1. To understand how habitat heterogeneity affects organisms, the present authors measured the response of chironomid life-histories to single patch types in a controlled laboratory experiment. The objective was to determine whether the size and type of leaf particles in the substratum affect development rate and survival of larvae, and the fecundity of the resulting adults.
2. Chironomus riparius larvae were raised in sand supplemented with dogwood, Cornus florida, (a rapid decomposer) or American sycamore, Platanus occidentalis, (a refractory decomposer) leaves fully crossed in a factorial design with four leaf particle sizes (0.2, 0.5, 1 and 5 cm²), or in sand only.
3. Development time was shorter in dogwood habitats than sycamore habitats, and shorter in sycamore habitats than in sand habitats. Survival was higher and larval head capsule lengths of instars III and IV were larger in dogwood than in sycamore or sand habitats. Development time was longer and head capsule lengths of instars III and IV were smaller in habitats with 5-cm² leaf particles than in 0.2-, 0.5- and 1-cm² particle size treatments. Female thorax length (a measure of fecundity) did not differ among treatments.
4. The present authors conclude that, for C. riparius confined to a single patch type, fitness is significantly enhanced when the patch contains small particles of dogwood (labile) leaves.     

中国双叶摇蚊亚属记述(双翅目,摇蚊科,摇蚊属)(英文)

对中国摇蚊属的双叶摇蚊亚属作了系统学记述。描述了2个新种:宽铗双叶摇蚊Chironomus(Camptochironomus)latusus sp.nov.和六毛双叶摇蚊Chironomus(Camptochironomus) senisetosus sp.nov.,重新描述了苍白双叶摇蚊Chironomus(Camptochironomus) pallidivittatus和伸展双叶摇蚊Chironomus(Camptochironomus) tentans。并编制了中国本亚属4种雄成虫分种检索表。宽铗双叶摇蚊,新种Chironomus(Camptochironomus) latusus sp.nov.(图1～2)雄虫生殖节构造与苍白双叶摇蚊相似,但本种肛尖两侧叶强烈骨化,抱器端节明显宽大。AR值明显小于后者(表2)。正模♂,内蒙古乌梁素海,1982-04-25,王新华灯诱。六毛双叶摇蚊,新种Chironomus(Camptochironomus) senisetosus sp.nov.(图5～6)雄虫生殖节构造与伸展双叶摇蚊相似,但可借以下特征区别于后者(表4):上附器发达,6根长刚毛有序地围绕并着生在上附器基部,肛节侧片毛缺失,腋瓣缘明显少于后者。正模♂,贵州省罗甸县,2004-08-11,于昕网捕。     

Life History of Ilybius fenestratus (Fabricius) (Coleoptera,Dytiscidae) in a Central Norwegian Lake

The life history of Ilybius fenestratus was studied in Målsj?en, a lake in S?r-Tr?ndelag, Central Norway (63°14'N, 10°26'E), during 1971–1972. Adults and larvae were sampled in activity traps every week during March–October and every 2–3 weeks during November–February. Newly-emerged adults were generally found from mid-July to September, and after overwintering in torpidity, probably in the water, they again appeared in the second half of June to August/September. Laying of eggs took place from early/mid July to early August. Larvae occurred in the traps from late July to early May. I. fenestratus was thus found to be a semivoltine summer breeder, with overwintering larvae the first winter and overwintering adults the next. Both adults and larvae lived in large areas of the lake's littoral zone.     

A new species of Chironomus Meigen, 1803 (Diptera,Chironomidae) from the southeast of Brazil

The article describes the larva, pupa, adults and karyotype of Chironomus reissi, sp. n., which live on leaf detritus beds of small temporary waters in the southeast of Brazil. The species belongs to the pseudothummi cytocomplex with the chromosome arm combination AE, BF, CD, G.     

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.     

Changes in trophic linkages to shortfin eels (<Emphasis Type="Italic">Anguilla australis</Emphasis>) since the collapse of submerged macrophytes in Lake Ellesmere,New Zealand

Lake Ellesmere (Te Waihora) is a nationally important coastal brackish lake in New Zealand, however degradation in water quality and loss of submerged macrophytes over past decades have raised concerns in regards to the declining status of the lake’s commercial and customary fisheries, predominantly targeted at shortfin eels (Anguilla australis). We investigated foodweb dynamics and trophic linkages to shortfin eels in Lake Ellesmere using a combination of abundance assessments, dietary studies, and stable isotope analyses. Data from our study are compared with historical data sets on benthic invertebrate community composition and shortfin eel diets to trace changes in the trophic linkages to top predators that have occurred since the late 1960s. Stable isotope analyses indicate that the foodweb is predominantly driven by epipelic and phytoplankton derived carbon sources, although it was difficult to discriminate between these two carbon pools because of wind-driven resuspension of lake sediments. Comparison of our survey results with historical data sets indicates a clear shift in benthic biota from being dominated by phytofaunal species such as Potamopyrgus antipodarum (comprising 90% of total invertebrate biomass) during the 1960s, to now being almost entirely comprised of subterranean species such as Chironomus zealandicus and oligochaetes (together comprising 82% of total invertebrate biomass). This shift in benthic communities has resulted in significant changes in the size-specific diet of juvenile shortfin eels (<400 mm) from those reported for Lake Ellesmere during the mid 1970s, with Chironomus larvae now comprising 65% of the diets of juvenile eels, whereas historically P. antipodarum was the dominant food item (>30% of total biomass). This shift towards foraging on smaller sediment-dwelling species could have implications for juvenile eel bioenergetics, and may help explain why juvenile shortfin growth rates have significantly decreased in past decades. Juvenile shortfins now appear to switch to foraging on preyfish (mainly common bullies, Gobiomorphus cotidianus) at a smaller size (≈400 mm) than historically recorded (>500 mm). Dietary and stable isotope signatures indicated that small shortfins (100–299 mm) have considerable overlap in trophic position (δ¹³C = −20.4‰, δ¹⁵N = 13.6‰) with common bullies (δ¹³C = −20.5‰, δ¹⁵N = 13.7‰), the dominant fish in Lake Ellesmere (92% of total abundance CPUE), potentially indicating that these two species may directly compete for food resources. These findings again highlighted the importance of C. zealandicus in sustaining the fish populations of the lake. Handling editor: S. Declerck     

Establishing laboratory cultures and performing ecological and evolutionary experiments with the emerging model species Chironomus riparius

Chironomus riparius is a well‐established model organism in various fields such as ecotoxicology and ecology, and therefore, environmental preferences, ecological interactions and metabolic traits are well‐studied. With the recent publication of a high‐quality draft genome, as well as different population genetic parameters such as mutation and recombination rate, the species can be used as an alternative to the Drosophila models in experimental population genomics or molecular ecology. To facilitate access to this promising experimental model species for a wider range of researchers, we describe experimental methods to first create and sustain long‐term cultures of C. riparius and then use them to perform repeatable and comparable experiments for various research questions.     

人工饲养背摇蚊幼虫龄数和龄期的测定

本文采用了人工饲养定期取样的方法,测定了背摇蚊Chironomus dorsalis(Anderson)幼虫的龄数以及各龄的龄期。分别测量不同发育阶段幼虫的头壳长、颏中齿顶端至冠突前缘间距离、头壳宽、颏宽、颏中齿宽、触角长、触角基节长、触角比(触角基节与其余各节的长度之比)等8项指标,以期得到区分和判定幼虫虫龄的最佳形态特征及指标。运用频次分布、均差分析和回归分析对8项指标测量数据进行统计分析,结果表明,背摇蚊幼虫可分4龄,触角长可作为理想的分龄特征和分龄指标,其次是颏中齿顶端至冠突前缘间距离和颏宽。利用种群众数龄期法计算1-4龄幼虫的平均龄期分别为1.32 d、2.00 d、7.51 d和8.39 d,幼虫期共为19.22 d。     

Succession of Chironomus Meigen Species (Diptera,Chironomidae) in Newly Filled Ponds

The colonization by Chironomus spp. of two ponds filled after a dry period was investigated. Field data were collected by means of quantitative benthic samples and emergence traps. C. melanescens. C. annularius, C. riparius, C. piger, C. luridus, C. obtusidens, C. plumosus, C. dorsalis and Camptochironomus tentans were determined cytotaxonomically in ponds investigated. C. melanescens and C. annularius appear to be the most characteristic species colonizing in high numbers in newly filled ponds. Larvae of C. annularius grew more slowly in ponds compared with the former one which resulted in a characteristic succession of both larval types. Most species mentioned disappeared completely from the ponds investigated after the metamorphosis of a single cohort. They were replaced by C. plumosus which was often attended by C. annularius in smaller ponds.     

Seasonal Dynamics of a Chironomus plumosus (L.) (Diptera,Chironomidae) Population from a Fish Pond in Southern Bohemia

A population of Chironomus plumosus (L.) from a fish pond has been investigated for two years. Quantitative benthic samples and emergence traps were used to study the seasonal dynamics. Effect of some factors on the duration of development was studied in laboratory experiments. Data on larval abundance, length frequency analysis and emergence of adults suggest a bivoltine life cycle. The population of C. plumosus investigated showed a pronounced tendency to dormancy, even under long-day conditions. Factors regulating the bivoltine life cycle are discussed.