Isolation and characterization of microsatellite markers in the caddisfly Drusus discolor (Trichoptera: Limnephilidae)

We describe the development of and amplification conditions for microsatellite primers isolated from the caddisfly Drusus discolor. Eight polymorphic microsatellite loci were developed and screened for variability using 37 individuals from two populations from central Europe. The primers yielded an average of 8.6 alleles per loci. No linkage disequilibrium between loci was detected, while three loci showed deviations from Hardy–Weinberg equilibrium in one of the two tested populations.     

Microsatellites for the net‐spinning caddisfly Plectrocnemia conspersa (Polycentropodidae)

Six polymorphic microsatellites were developed for the caddisfly Plectrocnemia conspersa from two enriched partial genomic libraries. These represent the first microsatellites published for the order Trichoptera. We show that, whilst it is possible to develop a highly enriched library, isolation of polymorphic microsatellites is difficult for this species, as has been found in some other of invertebrate groups. The genotypes of 160 individuals were determined using these new loci. Observed heterozygosities ranged from 0.013 to 0.788. Despite their problematic isolation, polymorphic microsatellite loci show greater levels of variation than previously studied allozyme markers.     

Substratum preference of the caddisfly Helicopsyche borealis (Hagen) (Trichoptera: Helicopsychidae)

The position of Helicopsyche borealis (Hagen) (Trichoptera: Helicopsychidae) larvae on the substratum surface is dependent on the current regime but varies with larval size. All size classes of larvae chose significantly different positions on the substratum under high versus low current velocities. All size classes preferred exposed surfaces under low current velocities. Small larvae preferred the upper surfaces of substrata under low current velocities and were physically displaced under high current velocities. Larger larvae also occurred on upper surfaces, but were more evenly dispersed over all surfaces than smaller larvae, and tended to aggregate on down-stream faces of rocks during high flow.     

Stream food web response to a salmon carcass analogue addition in two central Idaho, U.S.A. streams

1. Pacific salmon and steelhead once contributed large amounts of marine‐derived carbon, nitrogen and phosphorus to freshwater ecosystems in the Pacific Northwest of the United States of America (California, Oregon, Washington and Idaho). Declines in historically abundant anadromous salmonid populations represent a significant loss of returning nutrients across a large spatial scale. Recently, a manufactured salmon carcass analogue was developed and tested as a safe and effective method of delivering nutrients to freshwater and linked riparian ecosystems where marine‐derived nutrients have been reduced or eliminated. 2. We compared four streams: two reference and two treatment streams using salmon carcass analogue(s) (SCA) as a treatment. Response variables measured included: surface streamwater chemistry; nutrient limitation status; carbon and nitrogen stable isotopes; periphyton chlorophyll a and ash‐free dry mass (AFDM); macroinvertebrate density and biomass; and leaf litter decomposition rates. Within each stream, upstream reference and downstream treatment reaches were sampled 1 year before, during, and 1 year after the addition of SCA. 3. Periphyton chlorophyll a and AFDM and macroinvertebrate biomass were significantly higher in stream reaches treated with SCA. Enriched stable isotope (δ¹⁵N) signatures were observed in periphyton and macroinvertebrate samples collected from treatment reaches in both treatment streams, indicating trophic transfer from SCA to consumers. Densities of Ephemerellidae, Elmidae and Brachycentridae were significantly higher in treatment reaches. Macroinvertebrate community composition and structure, as measured by taxonomic richness and diversity, did not appear to respond significantly to SCA treatment. Leaf breakdown rates were variable among treatment streams: significantly higher in one stream treatment reach but not the other. Salmon carcass analogue treatments had no detectable effect on measured water chemistry variables. 4. Our results suggest that SCA addition successfully increased periphyton and macroinvertebrate biomass with no detectable response in streamwater nutrient concentrations. Correspondingly, no change in nutrient limitation status was detected based on dissolved inorganic nitrogen to soluble reactive phosphorus ratios (DIN/SRP) and nutrient‐diffusing substrata experiments. Salmon carcass analogues appear to increase freshwater productivity. 5. Salmon carcass analogues represent a pathogen‐free nutrient enhancement tool that mimics natural trophic transfer pathways, can be manufactured using recycled fish products, and is easily transported; however, salmon carcass analogues should not be viewed as a replacement for naturally spawning salmon and the important ecological processes they provide.     

Revision and synopsis of the caddisfly genus Dicosmoecus (Trichoptera: Limnephilidae; Dicosmoecinae)

Six species of Dicosmoecus are recognized: the palatus species group of Siberia and Japan [palatus (McL.), obscuripennis Banks, and jozankeanus Mats.)]; and the atripes species group of western montane North America [atripes (Hagen), gilvipes (Hagen), and pallicornis Banks]. D. obscuripennis is re‐established as a valid species distinct from palalus and recorded from the Yukon Territory and Alaska, and also Siberia. Keys are provided for identification of males, females, and larvae. Hypotheses of phylogeny and biogeography are proposed, stating that the palatus and atripes species groups evolved independently in Asia and North America respectively; and that obscuripennis of the palatus group extended its range to North America during the Pleistocene Beringian land connection between the two continents.

Data on food, life cycle, habitat, and distribution are given for the North American species. Most Dicosmoecus appear to be generalized predator‐shredders with robust, toothed mandibles; but fifth instar larvae of D. gilvipes feed mainly by scraping rocks for diatoms, a behaviour which is evidently responsible for eroding the slender blade and weakly formed teeth of the mandible, unique to this species, to a uniform scraping edge. D. gilvipes is further distinctive in usually having a 1‐year life cycle, whereas atripes and the other North American species usually have a life cycle of 2 years.     

Effects of larval energetic resources on life history and adult allocation patterns in a caddisfly (Trichoptera: Phryganeidae)

Abstract 1. How populations respond to environmental change depends, in part, on the connection between environmental variance during early life stages and its effect on subsequent life‐history traits. For example, environmental variation during the larval stage can influence the life histories of organisms with complex life cycles by altering the amount of time spent in each stage of the life cycle as well as by altering allocation to life‐history traits during metamorphosis. 2. The effects of larval energetic resources on developmental timing, adult mass, fecundity, mating success, and allocation to adult body structures (thorax, abdomen, wings) were examined in an aquatic caddisfly (Agrypnia deflata Milne, Trichoptera: Phryganeidae). Larval energetic reserves were manipulated by removing larval cases just prior to pupation. In the first experiment, cases of all individuals were removed just prior to pupation; experimental individuals were required to build a new case whereas control individuals were allowed to re‐enter their case without building. In the second experiment, energy differences were maximised between the two treatments by supplementing the larval diet of the control group and removing cases and not supplementing the diet of the experimental group. 3. Male and female development time, adult mass, and female fecundity were not influenced by case removal or diet supplementation. In contrast, allocation to adult body parts indicated a trade‐off between abdominal and thoracic mass among case‐removal females, suggesting that, under larval resource stress, females adjust resource allocation during metamorphosis to alleviate potential negative impacts on clutch size. In addition, latency to copulation increased when cases were removed, indicating larval resource stress could influence male mating success. 4. This study suggests that, under larval energetic stress, the negative impacts on female reproduction might be mitigated by re‐allocating resources during metamorphosis, whereas male allocation strategies might not be as flexible as female strategies.     

Structures on the antennal flagellum of a caddisfly,frenesia missa (Trichoptera,Limnephilidae)

Non-innervated macrotrichia and microtrichia, thick-walled chemoreceptors and three kinds of thin-walled chemoreceptors are present on the antennal flagellum of Frenesia missa. One of the thin-walled receptors, the plate organ, is of a type not previously recorded for any insect. About four times as many plate organs are present on the flagellum of the male as on that of the female. They occur also on the maxillary and labial palps.     

Ten polymorphic microsatellite loci isolated from the alpine caddisfly Allogamus uncatus Brauer (Trichoptera: Limnephilidae)

Here we report the development of 10 microsatellite loci for the alpine caddisfly, Allogamus uncatus. Polymorphism as detected in 24 individuals ranged from three to 17 alleles per locus, and observed heterozygosity ranged from 0.087 to 0.864. These primers will enable research on the genetic population structure of this species, the extent of gene flow among alpine permanent and temporary streams, and the genetic consequences of extinction/recolonization events.     

Metal exposures to native populations of the caddisfly Hydropsyche (Trichoptera: Hydropsychidae) determined from cytosolic and whole body metal concentrations

Metal concentrations of the soluble fraction of the cytoplasm (cytosol) and the whole body were determined in the caddisfly Hydropsyche spp. (Trichoptera). Metal accumulation in the cytosol and the whole body were compared in samples collected along 380 kms of a contamination gradient in the Clark Fork river in four consecutive years (1992–1995), and from a contaminated tributary (Flint Creek). Samples from the contaminated sites were compared to an uncontaminated tributary (Blackfoot River). Relations between cytosolic metal concentration and cytosolic protein (used as a general biomarker of protein metabolism) also were examined in 1994 and 1995. Relative to whole body concentrations, cytosolic metal concentrations varied among metals and years. Spatial patterns in whole body and cytosolic Cd, Cu and Pb concentrations were qualitatively similar each year, and these concentrations generally corresponded to contamination levels measured in bed sediments. The proportions of metals recovered in the cytosol of ranged from 12 to 64% for Cd and Cu and from 2 to 38% for Pb. Zinc in the whole body also was consistent with contamination levels, but cytosolic Zn concentrations increased only at the highest whole body Zn concentrations. As a result, the proportion of Zn recovered in the cytosol ranged from 16 to 63% and tended to be inversely related to whole body Zn concentrations. The proportions of cytosolic metals varied significantly among years and, as a result, interannual differences in metal concentrations were greater in the cytosol than in the whole body. The results demonstrated that Hydropsyche in the river were chronically exposed to biologically available metals. Some features of this exposure were not evident from whole body concentrations. In general, protein levels did not correspond to cytosolic metal concentrations. A variety of environmental factors could interact with metal exposures to produce complex responses in protein metabolism. Systematic study will be necessary to differentiate the effects of multiple environmental stressors on organisms living in contaminated ecosystems. This revised version was published online in July 2006 with corrections to the Cover Date.     

The life cycle of an introduced caddisfly,Cheumatopsyche pettiti (Banks) (Trichoptera: Hydropsychidae) in Waikolu Stream,Molokai, Hawaii

Hawaiian streams contain some of the most unique species of aquaticinvertebrates known. In the 1960's a North American net spinningcaddisfly, Cheumatopsyche pettiti was inadvertentlyintroduced and is found in most perennial streams on Oahu, Maui,Molokai and Kauai. We investigated the life cycle of thistemperately evolved caddisfly in Waikolu Stream, Molokai. The lifecycle of C. pettiti was interpreted as probably multivoltinewith continuous recruitment throughout the year. At all samplingdates, instars I–V were present as well as pupae and adults.Detritus accounted for >50% of the gut contents of all larvae.Diatoms and other algae accounted for the remaining 50% of thediet. Cheumatopsyche pettiti has also apparently adapted toextremes in stream flows by building smaller capture nets andrudimentary retreats, usually on bedrock or firmly embeddedcobble.     

Recruitment, kin and the spatial genetic structure of a caddisfly Plectrocnemia conspersa in a southern English stream

1. Our objectives were to examine small‐scale patterns in oviposition and genetic relatedness in a population of the stream‐dwelling caddis Plectrocnemia conspersa and, in particular, to look for any evidence of the spatial proximity of close kin and, therefore, ‘patchy recruitment’. 2. In order to examine the distribution of related larvae at the beginning of the aquatic phase, we searched the stream for egg masses. Spatially and temporally structured samples of larvae were then collected from the stream over four sample dates within one generation. The genetic relatedness of these field‐collected larvae, estimated using six polymorphic microsatellite loci, was subsequently compared with that of larvae reared from individual egg masses in the laboratory. 3. Egg masses were laid in clusters or ‘hot spots’ along the stream. The mean relatedness coefficient within reared egg masses ranged from 0.327 to 0.525, and differed significantly from that estimated for the population as a whole (0.070), indicating that the markers were sufficiently powerful to identify groups of siblings. Each egg mass was likely to be the progeny of one father, although the possibility of a small contribution from a second male could not be excluded for a few masses. 4. Mean relatedness within the spatially structured groups of larvae in the stream, even those in close proximity to each other, did not differ from the background population level estimate, suggesting that siblings disperse away from each other very quickly and that kin structure does not persist over time. 5. Changes in spatial genetic structure late in the larval life indicated that neighbouring larvae were less closely related than the population overall, possibly suggesting some direct or indirect means of avoiding kin when approaching the onset of pupation. 6. Our counts of egg masses suggested that survival through the egg stage and early larval life was apparently very high (>50%) for a non‐social insect, and may be a consequence of the colonial net that is briefly occupied by first instar larvae. 7. The number of egg masses laid in the stream (approximately 400 in the sample year), the lack of a spatial genetic structure showing evidence of families even early in larval life, and the high survival of eggs and early instar larvae, all refute the ‘patchy recruitment hypothesis’ for this species.     

Stable isotope evidence indicates the incorporation into Japanese catchments of marine‐derived nutrients transported by spawning Pacific Salmon

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The life history of Glyphopsyche irrorata (Trichoptera, Limnephilidae): A caddisfly that overwinters as an adult

Glyphopsyche irrorata has adapted to live in ponds with fluctuating water levels and ponds exhibiting winter drought by passing the winter as an adult in the terrestrial environment.
Larvae, which hatch in May and pupate in late August, are detritivorous shredders. Males and females emerge in September, with a sex ratio of one and commence mating in the autumn. The entire population has mated by May at which time females oviposit in the water. Adult males and females are present in equal numbers in the spring and have similar longevities approaching a maximum of 8 to 9 months.     

Effects of spawning Pacific salmon on terrestrial invertebrates: Insects near spawning habitat are isotopically enriched with nitrogen‐15 but display no differences in body size

When Pacific salmon (Oncorhynchus spp.) spawn and die, they deliver marine‐derived nutrient subsidies to freshwater and riparian ecosystems. These subsidies can alter the behavior, productivity, and abundance of recipient species and their habitats. Isotopes, such as nitrogen‐15 (¹⁵N), are often used to trace the destination of marine‐derived nutrients in riparian habitats. However, few studies have tested for correlations between stable isotopes and physiological responses of riparian organisms. We examined whether increases in δ ¹⁵N in terrestrial insect bodies adjacent to salmon spawning habitat translate to changes in percent nitrogen content and body size. This involved comparisons between distance from a salmon‐bearing river, marine‐derived nutrients in soils and insects, soil moisture content, and body size and nitrogen content in two common beetle families (Coleoptera: Curculionidae, Carabidae). As predicted, δ¹⁵N in riparian soils attenuated with distance from the river but was unaffected by soil moisture. This gradient was mirrored by δ¹⁵N in the herbivorous curculionid beetles, whereas carabid beetles, which feed at a higher trophic level and are more mobile, did not show discernable patterns in their δ¹⁵N content. Additionally, neither distance from the river nor body δ¹⁵N content was related to beetle body size. We also found that nitrogen‐15 was not correlated with total percent nitrogen in insect bodies, meaning that the presence of spawning salmon did not increase the percent nitrogen content of these insects. We conclude that while salmon‐derived nutrients had entered terrestrial food webs, the presence of δ¹⁵N alone did not indicate meaningful physiological changes in these insects in terms of percent nitrogen nor body size. While stable isotopes may be useful tracers of marine‐derived nutrients, they cannot necessarily be used as a proxy for physiologically important response variables.     

Effects of spawning Pacific salmon on the isotopic composition of biota differ among southeast Alaska streams

1. Adult Pacific salmon (Oncorhynchus spp.) transport marine nutrients to fresh waters and disturb sediments during spawning. The relative importance of nutrient fertilisation and benthic disturbance by salmon spawners can be modulated by environmental conditions (e.g. biological, chemical and physical conditions in the catchment, including human land use). 2. To determine the importance of the environmental context in modifying the uptake and incorporation of salmon‐derived material into stream biota, we measured the nitrogen (δ¹⁵N) and carbon (δ¹³C) isotopic composition of benthic algae (i.e. epilithon) and juvenile coho salmon (Oncorhynchus kisutch) in seven streams across a timber‐harvest gradient (8–69% catchment area harvested), both before and during the salmon run. Conditional bootstrap modelling simulations were used to assess variability in the response of epilithon and juvenile coho salmon to spawning salmon. 3. In response to spawning salmon, epilithon exhibited enrichment in both δ¹⁵N (mean: 1.5‰) and δ¹³C (2.3‰). Juvenile coho were also enriched in both δ¹⁵N (0.7‰) and δ¹³C (1.4‰). Conditional bootstrap models indicate decreased variation in data as spatial replication increases, suggesting that the number of study sites can influence the results of Pacific salmon isotope studies. 4. Epilithon isotopic enrichment was predicted by environmental conditions, with δ¹⁵N enrichment predicted by stream temperature and timber harvest (R² = 0.87) and δ¹³C enrichment by discharge, sediment size, timber harvest and spawner density (R² = 0.96). Furthermore, we found evidence for a legacy effect of salmon spawners, with pre‐spawner δ¹⁵N and δ¹³C of both epilithon and juvenile coho predicted by salmon run size in the previous year. 5. Our results show that the degree of incorporation of salmon‐derived nitrogen and carbon differs among streams. Furthermore, the environmental context, including putative legacy effects of spawning salmon, can influence background isotopic concentrations and utilisation of salmon‐derived materials in southeast Alaska salmon streams. Future studies should consider the variation in isotopic composition of stream biota when deciding on the number of study sites and samples needed to generate meaningful results.     

Synonymic Notes on a Japanese Hydatophylax (Trichoptera: Limnephilidae)

Stenophylax festivus Navás, 1920 is transferred to genus Hydatophylax and Hydatophylax intermedius Schmid, 1964 is its junior synonym. Matsumura (1931) incorrectly recorded this species as Astenophylax grammicus McLachlan from Hokkaido, Japan.