Barriers to the recovery of aquatic insect communities in urban streams

1. Worldwide, increasing numbers of stream restoration projects are being initiated to rehabilitate waterways modified by urbanisation. However, many of these projects have limited success in restoring stream communities. Prompted by this, we investigated previously unrecognised barriers to aquatic insect colonisation in urban streams. 2. To investigate whether the availability of suitable substrata for oviposition limited the longitudinal distribution of caddisflies, large boulders were added to the upstream reaches of one stream. Prior to the addition, more egg masses were observed downstream and this longitudinal pattern persisted subsequently. 3. Malaise trapping revealed that adult caddisfly diversity and abundance was greater downstream than upstream. Furthermore, in a previous study the authors found larval caddisflies reflected the longitudinal distribution of adults. 4. The only obvious potential obstructions between reaches were roads beneath which the stream flowed through culverted crossings. Malaise trapping was used to examine the effect of road culverts and bridges on caddisfly dispersal. Numbers of caddisflies caught declined upstream and about 2.5 × more individuals were taken in traps immediately below than above five culverts. 4. Bridges, which had a more open structure than culverts, had no significant effect on the size of catches made above and below them. 5. Road culverts could act as partial barriers to upstream flight, with consequences for larval recruitment in urban streams. We recommend that urban planners and designers of restoration projects consider possible synergistic effects of poor oviposition habitat and barriers to aquatic insect dispersal, which may be critical for the colonisation of urban headwater streams and for the maintenance of stream insect populations.     

Effect of the filling season on aquatic plants in Mediterranean temporary ponds

Aims Pond environmental conditions may differ among years with regards to the season in which ponds begin to fill. We experimentally evaluated how seedling emergence, plant growth and phenology differed among years in which filling occurred in winter, autumn or spring.Methods We collected sediments from a natural temporary pond and located them in aquariums. They were placed in a climatic chamber that simulated annual variation in field environmental temperatures and light conditions. Aquariums were assigned to one of three treatments, which differed in the date on which they were filled with water (autumn, winter and spring). We counted the number of seedlings of different species emerged and recorded data about the presence of flowers, seeds or spores every week. The experiment was finished in June, when we harvested the plants and estimated their biomass.Important findings In most species, seedling emergences were primarily related to time after filling, and thus synchronized their life cycles with the unpredictably timed wet phase of the ponds. Autumn filling resulted in the highest numbers of seeds/spores. However, winter filling promoted plant growth the most. In the spring filling treatment, more terrestrial plant seedlings emerged and fewer seeds/spores were produced. When ponds are flooded earlier, plants may produce a higher number of propagules. However, in years when inundation is delayed to spring and hydroperiods are short, seedling emergence deplete the seed bank and there is little to no seed production, while terrestrial monocots are able to colonize pond basin.     

Germination characteristics and sporeling success of Azolla filiculoides Lamarck, an aquatic invasive fern, in a Mediterranean temporary wetland

Spore germination characteristics of Azolla filiculoides Lamarck, a recent invader of the Doñana Mediterranean wetlands, have been quantified experimentally. Batches of spores were subjected to different storage conditions, salinity concentrations, phosphorus availability and drought effects. Cold pre-treatment did not stimulate spore germination, whereas drought, a characteristic different from Azolla's native habitat, reduced it (40 ± 7 vs 13 ± 5). Germination declined with the increase of salinity (r = −0.50, notably above 5000 μS cm⁻¹), whereas phosphorus availability had no significant effect.     

A preliminary study of aquatic insect communities and leaf decomposition in acid streams near Dorset,Ontario

Some streams near Dorset in south-central Ontario suffer from acid precipitation via run-off and seepage from thin soils with little buffering capacity. A spring-summer survey of eight headwater streams revealed some characteristics of their insect communities which could be correlated with pH. The streams could be divided into three groups according to pH and community structure. In the most acid group (annual pH range 4.3–4.8), Ephemeroptera were absent from two streams although mature Leptophlebia were collected just after spring thaw from the most acid one (pH 4.3–4.5). One of these three streams also lacked Plecoptera but the others had two or three genera, all shredders. The second group of three streams (pH 5.0–6.3), with one exception, did support Ephemeroptera (3–4 genera) and Plecoptera (1–4 genera), most of the latter being shredders. In all six of these acid streams, Trichoptera were more diverse and more dense than Ephemeroptera and Plecoptera; again, shredders were clearly dominant, especially the limnephilid caddisfly, Frenesia difficilis (Walker). These six streams also had similar chironomid communities (densities were an order of magnitude higher than other insects). Dominance by Chironomini and abundant Tanypodinae typified the most acid streams. In contrast, the two streams in the third group (pH 5.3–6.7) had richer and more balanced communities in general with relatively fewer shredders (no Frenesia), more collectors, and fewer Chironomini and Tanypodinae. As a field experiment showed that autumn-shed leaves decomposed more slowly in acid than in non-acid streams, summer-growing shredders may benefit from the pulse of acidity at snowmelt.     

Monitoring the acoustic activity of an aquatic insect population in relation to temperature,vegetation and noise

1. Acoustic population monitoring is a noninvasive method that can be deployed continuously over long periods of time and at large spatial scales. One of the newly discovered threats acting on biological diversity is anthropogenic noise. High levels of anthropogenic noise occur in aquatic environments, yet their effects on animals living in freshwater habitats have very rarely been investigated.
2. Here, we used acoustic monitoring and automatic detection to assess the acoustic activity of a population of a soniferous freshwater insect.
3. The sounds emitted by the corixid Micronecta scholtzi were recorded in a Mediterranean pond with an array of 12 hydrophones. An automatic analysis based on a measure of the amplitude found in the frequency band of M. scholtzi was developed to assess the level of acoustic activity. We used functional linear models, accounting for the periodicity of the calling behaviour, to estimate the possible effect of temperature, vegetation and a noise due to an immersed engine.
4. The automatic analysis was validated as an efficient method to measure the acoustic activity. The monitoring revealed a clear 24-hr pattern in the acoustic activity of M. scholtzi and three peaks of activity during the morning. Functional linear models revealed negative effects of both temperature and vegetation and showed that an engine noise, played back for 2 hr during the night, elicited an increase in the level of acoustic activity of the population. Moreover, a cross-correlation procedure showed that noise delayed the acoustic activity of the population.
5. Our results suggest that acoustic survey and automatic detection are efficient methods to monitor the acoustic activity of an insect population especially in response to an anthropogenic disturbance.

     

Reduced flight capability in British Virgin Island populations of a wing-dimorphic insect: the role of habitat isolation, persistence, and structure

1. The effects of habitat isolation, persistence, and host‐plant structure on the incidence of dispersal capability (per cent macroptery) in populations of the delphacid planthopper Toya venilia were examined throughout the British Virgin Islands. The host plant of this delphacid is salt grass Sporobolus virginicus, which grows either in undisturbed habitats (large expanses on intertidal salt flats and around the margins of salt ponds, or small patches of sparse vegetation on sand dunes along the shore), or in less persistent, disturbed habitats (managed lawns). 2. Both sexes of T. venilia were significantly more macropterous in disturbed habitats (77.1% in males, 12.5% in females) than in more persistent, undisturbed habitats (19.2% in males, < 1% in females). 3. Males exhibited significantly higher levels of macroptery (26.9 ± 7.6%) than did females (2.0 ± 1.7%), and per cent macroptery was positively density dependent for both sexes in field populations. 4. There was no evidence that the low incidence of female macroptery in a subset of island populations inhabiting natural habitats (1.7 ± 1.2%) was attributable to the effects of isolation on oceanic islands. The incidence of macroptery in British Virgin Island populations of T. venilia was not different from that observed in mainland delphacid species existing in habitats of similar duration. 5. Rather, the persistence of most salt grass habitats throughout the British Virgin Islands best explains the evolution of flight reduction in females of this island‐inhabiting delphacid. 6. Males were significantly more macropterous in populations occupying dune vegetation (37.6 ± 9.8%) than in populations occupying salt flat–pond margin habitats (7.6 ± 5.6%). By contrast, females exhibited low levels of macroptery in both dune (0%) and salt flat–pond margin (< 1%) habitats. Variation in salt‐grass structure probably underlies this habitat‐related difference in macroptery because flight‐capable males of planthoppers are better able to locate females in the sparse‐structured grass growing on dunes. This habitat‐related difference in male macroptery accounted for the generally higher level of macroptery observed in males than in females throughout the islands. 7. The importance of habitat persistence and structure in explaining the incidence of dispersal capability in T. venilia is probably indicative of the key role these two factors play in shaping the dispersal strategies of many insects.     

Effects of exported seston on aquatic insect faunal similarity and species richness in lake outlet streams in Montana,USA

The quantity of seston exported from a lake affected the qualitative composition and species richness of aquatic insects in 13 lake outlet streams in northwestern Montana. Mean values for chlorophyll and particulate organic carbon in lake effluent waters ranged from 0.5 to 2.7 and 80 to 601 mg m^-3, respectively. Correlations between a detrended correspondence analysis of faunal similarities in outlet streams and measures of organic export from the lake indicated that distributional patterns were primarily dependent upon the general trophic status of the lakes. A comparison of faunal assemblages at stream stations located at the outlet and 100 m downstream demonstrated that species composition at the two stations was more similar in productive systems.     

Decrease of fluctuating asymmetry among larval instars in an aquatic, holometabolous insect

The use of fluctuating asymmetry (FA) to reveal environmental stress in natural populations has been investigated extensively over the past decade. In aquatic ecosystems, many investigations involve amphibiotic insects with larval development stages in freshwater. To explain the important variability in study results, we investigated the FA level of a natural Hydropsyche exocellata (Insecta: Trichoptera) population at four different stages, from first larval instar to adult. The level of FA decreased between larval stages, but remained constant between the last larval instar and the adult. The presence of a compensational growth mechanism and the elimination of asymmetric individuals by natural selection are two hypotheses that could explain this observation.     

Relative importance of Conservation Reserve Programs to aquatic insect biodiversity in an agricultural watershed in the Midwest,USA

Hydrobiologia - The Conservation Reserve Program (CRP) and the Conservation Reserve Enhancement Program (CREP) in the USA offer farmers government financial incentives to take erosive agricultural...     

Determination of freedom-from-rabies for small Indian mongoose populations in the United States Virgin Islands, 2019–2020

Mongooses, a nonnative species, are a known reservoir of rabies virus in the Caribbean region. A cross-sectional study of mongooses at 41 field sites on the US Virgin Islands of St. Croix, St. John, and St. Thomas captured 312 mongooses (32% capture rate). We determined the absence of rabies virus by antigen testing and rabies virus exposure by antibody testing in mongoose populations on all three islands. USVI is the first Caribbean state to determine freedom-from-rabies for its mongoose populations with a scientifically-led robust cross-sectional study. Ongoing surveillance activities will determine if other domestic and wildlife populations in USVI are rabies-free.     

Mutation of a critical tryptophan to lysine in avidin or streptavidin may explain why sea urchin fibropellin adopts an avidin-like domain

Sea urchin fibropellins are epidermal growth factor homologues that harbor a C-terminal domain, similar in sequence to hen egg-white avidin and bacterial streptavidin. The fibropellin sequence was used as a conceptual template for mutation of designated conserved tryptophan residues in the biotin-binding sites of the tetrameric proteins, avidin and streptavidin. Three different mutations of avidin, Trp-110-Lys, Trp-70-Arg and the double mutant, were expressed in a baculovirus-infected insect cell system. A mutant of streptavidin, Trp-120-Lys, was similarly expressed. The homologous tryptophan to lysine (W-->K) mutations of avidin and streptavidin were both capable of binding biotin and biotinylated material. Their affinity for the vitamin was, however, significantly reduced: from K(d) approximately 10(-15) M of the wild-type tetramer down to K(d) approximately 10(-8) M for both W-->K mutants. In fact, their binding to immobilized biotin matrices could be reversed by the presence of free biotin. The Trp-70-Arg mutant of avidin bound biotin very poorly and the double mutant (which emulates the fibropellin domain) failed to bind biotin at all. Using a gel filtration fast-protein liquid chromatography assay, both W-->K mutants were found to form stable dimers in solution. These findings may indicate that mimicry in the nature of the avidin sequence and fold by the fibropellins is not designed to generate biotin-binding, but may serve to secure an appropriate structure for facilitating dimerization.     

Genetic background of enhanced radioresistance in an anhydrobiotic insect: transcriptional response to ionizing radiations and desiccation

Extremophiles - It is assumed that resistance to ionizing radiation, as well as cross-resistance to other abiotic stresses, is a side effect of the evolutionary-based adaptation of anhydrobiotic...     

A study of the relationship between aquatic insect growth and water temperature in a small stream

The growth of aquatic insects in a small mountain stream was studied with emphasis on water temperature. Growth of the five dominant species was examined in relation to degree-days. This measure accounts for time and the minimum temperature necessary for insect growth. All species showed reduced specific growth rates with lower temperatures, but some (Ephemerella dorothea, Leuctra tenella, Neumoura wui) did not stop growing at even the lowest water temperatures. Both Diplectrona modesta and Paraleptophlebia assimilis had minimum growth temperatures. Studies demonstrated that the growth of stream insects is directly proportional to the number of degree-days experienced by a population.     

Disturbance,fish, and variation in the predatory insect guild of coastal streams

Species distributions, and thus the composition of communities, are determined by many interacting biotic and abiotic factors. We analyzed the variation in composition of the invertebrate predator guild across eight small, steep coastal streams in eastern Canada, in relation to variation in several broad categories of environmental variables: disturbance-related physical characteristics, top-down effects (fish), and bottom-up effects (prey composition and productivity-related physical/chemical variables). Similarity in composition (relative and absolute abundances of the 19 species belonging to the Rhyacophilidae, Perlodidae, and Chloroperlidae) declined significantly with distance. Streams that were most similar in predator composition were also most similar in physical factors related to disturbance, but were not more similar in prey abundance/composition or in environmental factors associated with productivity (chemistry, canopy cover, and riparian forest type). Similarity in the relative abundance of species within the Rhyacophilidae was linked to variation in the presence/abundance of brook trout. These results suggest that the invertebrate predator guilds of these small coastal streams are structured first and foremost by factors associated with the magnitude and variability of the flow regime, and second by response to top-down factors (predation by brook trout). There was no evidence that bottom-up effects altered the composition or abundance of the predator guild. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: Sonja Stendera     

Effects of insect predators on small populations of Aphis fabae in the field

Predators (mostly staphylinid larvae) almost completely eliminated small initial colonies of Aphis fabae on beans (Vicia faba) in the field during a summer unfavourable to the aphid's rapid multiplication. Syrphid larvae must have travelled considerable distances from other plants. A method of labelling single apterous adult aphids with a radioisotope for their detection in the field is described.

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Zusammenfassung Während eines für rasche Vermehrung von Blattläusen ungünstigen Sommers wurden kleine Initialkolonien von Aphis fabae auf einem Feldbestand von Ackerbohnen (Vicia faba) durch das unerwartete Eingreifen räuberischer Insekten fast vollständig vernichtet. Die häufigsten Räuber waren Staphyliniden-Larven, welche — zusammen mit Syrphiden-Larven — wahrscheinlich nicht entdeckt worden wären, wären die Blattläuse nicht in einem der Versuche in kleine Käfige eingeschlossen gewesen, in die die Räuber durch die engen Musselingewebe-Maschen eindringen konnten. Die Räuber schlüpften durch die Maschen, fraßen die Aphiden und wurden dabei zu dick, um zu entkommen. Syrphiden-Larven, die gewöhnlich als relativ träge Räuber gelten, wurden auch in den Käfigen angetroffen. Sie mußten aus beträchtlichen Entfernungen von anderen Pflanzen herbeigekrochen sein. Es wird eine Methode beschrieben, die es gestattet, einzelne erwachsene aptere A. fabae so zu markieren, daß sie im Freiland wiedergefunden werden können.

     

Abnormalities in the tracheal gills of aquatic insects collected from streams receiving chlorinated or crude oil wastes

SUMMARY. Altered tracheal gills were found on some specimens of Phasganophora capitata (Plecoptera: Perlidae) and net-spinning caddisflies (Trichoptera: Hydropsychidae) collected from streams in New York State. At one location only the basal portion remained of the normally highly-branched structures. At another location the gills were impregnated with a tar-like substance. Chlorine and crude oil are the suspected causal agents.     

DNA base changes induced following in vivo exposure of unadapted, adapted or ada- Escherichia coli to N-methyl-N'-nitro-N-nitrosoguanidine

The adaptive response is one of the major repair pathways in Escherichia coli that removes DNA alkylation damage. To investigate the role of the adaptive response in mutagenesis, the E. coli gpt forward mutation assay system was used to determine the mutation spectrum of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in MNNG-adapted and unadapted GP120 (wild-type) and unadapted PJ5 (ada-5) cells. We observed that 34/37 mutations in the unadapted GP120 cells, 38/40 mutations in the adapted GP120 cells, and 10/10 mutations in the PJ5 cells were GC----AT transitions. The remaining 3/37 mutations in the unadapted GP120 cells were large insertions. The remaining 2/40 mutations in the adapted GP120 cells were transversions with one a GC----CG and the other an AT----CG. A surrounding sequence specificity of mutagenesis was observed for the GC----AT transitions in both the unadapted (GP120 and PJ5) and adapted (GP120) cells, with 70% of the unadapted PJ5, 68% of the unadapted GP120, and 61% of the adapted GP120 mutations occurring at the middle G of the sequence 5'--GG(A or T)--3'. Both strains also displayed a statistically significant preference for mutagenesis at guanine bases in the non-transcribed strand. The overall distribution of mutated sites in the gpt gene in adapted and unadapted cells was similar, although the rate of mutations at certain sites appeared different. These minor differences could result from either non-uniform repair of alkylation damage at different sites on the DNA, or altered processing of the alkylated bases to mutations in the adapted state.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ecology of streams draining forested and non-forested catchments in an area of central Scotland subject to acid precipitation

A study of 12 streams draining forested and non-forested catchments was made in an area of central Scotland where slow-weathering bedrock was predominantly quartzite, schists and slates. Sitka spruce (Picea sitchensis Carriere) was the most common tree species. Precipitation in the area had an annual mean pH in the range 4.3–4.5. Streams within the planted zone were always more acid than those outside and had higher concentrations of aluminium and manganese. With one exception, trout were absent from streams within long-established forests and planted salmon eggs (Salmo salar L.) died within a few weeks. A high proportion of such eggs survived in streams outside the forest. Siphlonurus lacustris Eaton was the only mayfly nymph found in the most acid streams in summer collections. In winter samples, mayfly nymphs, Heptagenia lateralis (Curtis) were found in only one forest stream but several species were present in the non-forested catchments. It is suggested that spruce forests can effectively collect acid pollutants which are subsequently washed out, thus accelerating the acidification of the soil. Streams therefore become increasingly acid as the neutralisation capacities of their catchments decrease.     

Life syndrome of the bryophyte communities as an adaptative pattern in the Mediterranean temporary ponds of Italy

An ecological and biological investigation on the bryophyte communities of the Mediterranean temporary ponds was carried out in Italy. Here, the occurrence of a rich set of liverworts is very significant, as several species of Riccia characterize the communities from a physiognomical, ecological and syntaxonomical point of view. The moss component is represented only by acrocarpous mosses, e.g. Archidium alternifolium and Pleuridium acuminatum which play an important phytosociological role. In this study, the bryophyte communities are used to identify a pattern, corresponding to a “functional type” which reflects the correlated response of the bryophyte communities toward the prevalent ecological parameters of the habitat. The individuated functional type assembles life strategy, life form, lifespan, spore size, dispersal strategy, reproduction effort, independently from the taxonomical relationship of the species characterizing the communities. It represents an adaptative pattern of coevolved characters, adopted by the bryophyte communities for the habitat establishment and re-establishment following the seasonal water fluctuations typical of the investigated habitat.