Xenochironomus canterburyensis (Diptera: Chironomidae), a commensal of Hyridella menziesi (Lamellibranchia) in Lake Taupo; features of pre-adult life history

Abstract

The larvae and pupae of the univoltine chironomid Xenochironomus canterburyensis (Freeman) are inquiline commensals of the freshwater mussel Hyridella menziesi (Gray). The 1st- and 2nd-instar larvae enter the mantle/valve cavity of the mussel in midsummer, and by early winter migrate as 3rd-instar larvae to the posterior end of the valve to lodge near its margin beside the inhalant siphon. During the spring, growth of the periostracum of the valve margin between the larva and the mantle of the mussel leaves the 4th-instar larva outside the mantle/valve cavity, where it pupates before leaving the mussel for the lake surface and adult emergence.     

Reciprocal Effects between Burying Behavior of a Larval Dragonfly (Odonata: Macromia illinoiensis) and Zebra Mussel Colonization

Invasive zebra mussels (Dreissena polymorpha) often colonize dragonfly larvae, especially spawling species whose survivorship to emergence as terrestrial predators is consequently reduced. Using individuals of the sprawler, Macromia illinoiensis, as their own controls, we compared the burying behavior of penultimate instar larvae before (i.e. baseline) and after their colonization by zebra mussels under ambient conditions. Individuals that took longer to bury themselves when mussel-free had a higher rate of colonization by mussels over a five-day period compared to those that buried faster. In contrast, the depth at which individuals buried when mussel-free was not predictive of subsequent colonization rate. Although mean bury time did not differ between baseline and when an individual carried one or more mussels, colonized larvae buried more shallowly than when mussel-free. Moreover, attached mussels increased the risk of subsequent colonization by zebra mussels. After naturally losing all of their attached mussels, bury time and depth of individuals did not differ from their baseline behavior, indicating that the changes in the behavior of colonized individuals were due to mussel loads and not their time in captivity. Under natural conditions, the positive feed-back between mussel attachment and increasing vulnerability to colonization helps explain how mussel loads, which are lost at molting, can accumulate quickly over the duration of the final larval stadium. Because zebra mussel attachment decreases the crypsis that that a M. illinoiensis gains from burying, the invasive mussel may also make dragonfly larvae more detectable to visual predators.     

The costs and benefits in an unusual symbiosis: experimental evidence that bitterling fish (Rhodeus sericeus) are parasites of unionid mussels in Europe

Interspecific symbiotic relationships involve a complex network of interactions, and understanding their outcome requires quantification of the costs and benefits to both partners. We experimentally investigated the costs and benefits in the relationship between European bitterling fish (Rhodeus sericeus) and freshwater mussels that are used by R. sericeus for oviposition. This relationship has hitherto been thought mutualistic, on the premise that R. sericeus use mussels as foster parents of their embryos while mussels use R. sericeus as hosts for their larvae. We demonstrate that R. sericeus is a parasite of European mussels, because it (i) avoids the cost of infection by mussel larvae and (ii) imposes a direct cost on mussels. Our experiments also indicate a potential coevolutionary arms race between bitterling fishes and their mussel hosts; the outcome of this relationship may differ between Asia, the centre of distribution of bitterling fishes, and Europe where they have recently invaded.     

Preferences of the Ponto-Caspian amphipod Dikerogammarus haemobaphes for living zebra mussels

A Ponto-Caspian amphipod Dikerogammarus haemobaphes has recently invaded European waters. In the recipient area, it encountered Dreissena polymorpha , a habitat-forming bivalve, co-occurring with the gammarids in their native range. We assumed that interspecific interactions between these two species, which could develop during their long-term co-evolution, may affect the gammarid behaviour in novel areas. We examined the gammarid ability to select a habitat containing living mussels and searched for cues used in that selection. We hypothesized that they may respond to such traits of a living mussel as byssal threads, activity (e.g. valve movements, filtration) and/or shell surface properties. We conducted the pairwise habitat-choice experiments in which we offered various objects to single gammarids in the following combinations: (1) living mussels versus empty shells (the general effect of living Dreissena ); (2) living mussels versus shells with added byssal threads and shells with byssus versus shells without it (the effect of byssus); (3) living mussels versus shells, both coated with nail varnish to neutralize the shell surface (the effect of mussel activity); (4) varnished versus clean living mussels (the effect of shell surface); (5) varnished versus clean stones (the effect of varnish). We checked the gammarid positions in the experimental tanks after 24 h. The gammarids preferred clean living mussels over clean shells, regardless of the presence of byssal threads under the latter. They responded to the shell surface, exhibiting preferences for clean mussels over varnished individuals. They were neither affected by the presence of byssus nor by mussel activity. The ability to detect and actively select zebra mussel habitats may be beneficial for D. haemobaphes and help it establish stable populations in newly invaded areas.     

The Behavioural Responses by Larvae of the Water Mite Unionicola Foili (Acari: Unionicolidae) to Gravity, Light and Host Chemicals: Adaptations for Transmission Success?

The life cycle of the water mite Unionicola foili includes larvae that parasitize chironomid dipterans, and nymphs and adults that occur in association with the freshwater mussel Utterbackia imbecillis. The georesponses and photoresponses of larval U. foili in the presence of chemical substances from chironomids and mussels both prior to (= pre-chironomid larvae) and after their parasitism with chironomids (= post-chironomid larvae) were examined in the laboratory. The responses of larval U. foili to light and gravity changed during larval ontogeny and varied depending on the chemistry of the medium in which they were examined. Pre-chironomid larvae preferentially responded to water modified by chironomids given that negative phototaxis and positive georesponses were elicited only in the presence of water that had been modified by these hosts. Post-chironomid larvae exhibited host-induced negative phototaxis only in the presence of mussel-modified water. Post-chironomid larvae were consistently geopositive when exposed to water modified by mussels or chironomids. The pattern of responses exhibited by larval U. foili to light and gravity are interpreted as adaptations for locating potential hosts in the field.     

Selective settlement of the barnacle Semibalanus balanoides (L.) facilitates its growth and reproduction on mussel beds in the Wadden Sea

On the unstable sedimentary tidal flats of the Wadden Sea, a suitable attachment substrate for sessile organisms is generally lacking. Epibenthic mussel beds (Mytilus edulis L.) provide the only and strongly limited settlement sites available for the barnacle, Semibalanus balanoides (L.). Field investigations showed that barnacles were non-randomly distributed within a mussel bed. They preferentially occurred near the siphonal apertures of living mussels but rarely grew on dead mussels or shell fragments. Field experiments revealed that this was due to selective settlement of barnacle cyprid larvae. Growth of barnacles was significantly higher upon living mussels than on empty mussel shells. Moreover, a higher reproductive output was obtained by individuals on living mussels which produced twice as many nauplii larvae than barnacles attached to empty shells. This study shows that selective settlement of S. balanoides cyprid larvae on living mussels is adaptive with respect to individual fitness. Received in revised form: 15 January 2001 Electronic Publication     

Cohort studies on mosquito (Diptera: Culicidae) larvae living in the water-filled floral bracts of Heliconia aurea (Zingiberales: Musaceae)

Abstract. 1. An experimental and observational study of the three species of mosquito larvae living in the water-filled floral bracts of Heliconia aurea at Rancho Grande, Venezuela, was designed to determine if each mosquito species forms instar cohorts and excludes conspecifics of younger instars. This study was motivated by a statement of Maguire (1971) who suggested that mosquito larvae in Puerto Rican Heliconia inflorescences form instar cohorts and exclude younger mosquitoes from the floral bracts.
2. Field observations of naturally occurring populations of mosquito larvae from fifty-three H.aurea inflorescences give no indication that cohorts are formed for Wyeomyia felicia and Culex bihaicolus . However, there is strong evidence that cohorts of Trichoprosopon digitatum occur. These cohorts are not structured by larval competition but by female preference of the youngest bracts as oviposition sites and by large T.digitatum larvae feeding on smaller con-specifics.
3. Field experiments show that first instar W.felicia and C.bihaicolus survive as well over a 6 day period in the presence of third instar conspecifics as they do when all mosquito larvae in an experimental bract are first instars.     

Hierarchical spatial structure in soft-bottom mussel beds

Mussels (Mytilus edulis L.) are unusual because they thrive in both rocky shore and soft-bottom habitats. Despite their ecological and economic importance, little is known about their spatial structure. Mussels do not generally recruit to bare soft substrate because larvae and postlarvae cannot attach to a bottom of small sediment particles. They attach to hard objects on the sediment surface (especially other mussels), so soft-bottom mussel beds may be spatially organized in ways that are fundamentally different from those on rocky shores. The purpose of our study was to characterize the scales of spatial variability for several mussel abundance parameters in soft-bottom, intertidal M. edulis beds in coastal Maine. We used a random factor nested-ANOVA design of 200 cm² Cores within 1 m² Quadrats within 6 m Transects within Positions within bed Sites along 70 km (euclidean distance) of the Maine coast. Based on the literature and our field observations, we hypothesized that Sites and Positions account for most of the spatial variance in soft-botttom mussel beds. We rejected this hypothesis. Sites and Positions were not important in explaining variation in total mussel density, density of new recruits, or density of larger mussels. Although most of the variance in surface silt-clay fraction did occur at these levels, most mussel variation occurred at smaller spatial scales, specifically at the Quadrat scale for new recruits and total mussels and at the Transect scale for larger mussels. Variance in mussel parameters was not closely linked to the silt-clay fraction of surface sediment or to Site rankings of wind exposure and tidal flow. Variance in total mussel density was due primarily to variance in recruitment. No single scale explained more than about half the mussel variance, and no single scale was best at explaining all the mussel parameters. Greater knowledge about mussel bed spatial variability would be useful because it can help direct scale-dependent sampling regimes, field experiments, and coastal management practices.     

Parasitic freshwater pearl mussel larvae (Margaritifera margaritifera L.) reduce the drift-feeding rate of juvenile brown trout (Salmo trutta L.)

In this paper we describe, for the first time, the effects of freshwater pearl mussel (Margaritifera margaritifera L.) encystment on the drift-feeding behavior of juvenile brown trout (Salmo trutta L.). Because both mussel and salmonid populations are often threatened, this study not only adds knowledge to the understanding of host-parasite systems, but it is also of conservation value. Individual trout, mussel-encysted (25.1?±?5.7 larvae?·?g^?1 body weight, n?=?5) or non-encysted (n?=?5), were fed with chironomid larvae in a flow-through stream aquarium. Feeding trials were filmed and analyzed by counting the numbers of chironomid larvae each individual ate, and by estimating the prey-capture distance. Non-encysted trout had a significantly higher drift-foraging rate than did encysted trout, and they captured significantly more prey further away from their focal point. The reduced foraging success of encysted trout was mainly due to their failure to catch prey relatively further from their focal point. This suggests that reduced foraging success of encysted trout may be due to poorer energetic status, but the physical effects of mussel larvae on prey handling time cannot be ruled out. Encysted trout caught approximately 20 % fewer prey, which would result in a reduction in growth potential during the period of mussel encystment. Reduced energetic status might also result in reduced competitive ability or in increased exposure to predation risk.     

Biology of Microplitis kewleyi (Hymenoptera: Braconidae): A parasite of Agrotis ipsilon (Lepidoptera: Noctuidae) larvae

Microplitis kewleyi Muesebeck is a gregarious internal parasite of larvae of the black cutworm Agrotis ipsilon (Hufnagel). Studies of the biology of the parasite revealed that there was an inverse relationship between host instar and parasite preference. Duration of development from egg to pupa ranged from 18 days at 27°C to 68.7 days at 16°C. Development from egg to pupa took 13.5–21.6 days when fourth and first instar host larvae, respectively, were parasitized. A larger number of parasites emerged from hosts parasitized in the fourth instar (22.4) than the first instar (11.5). Parasite pupation occurred when the host was in the fifth/sixth instar, depending on the instar parasitized. Thirty‐nine per cent of host larvae exposed as first instars to parasites died before parasite emergence. This decreased to 0% for host larvae exposed as fourth instars. The sex ratio was 1:1.2 (M:F). Thirty‐seven per cent of hosts exposed diurnally were stung, compared to 24% exposed nocturnally. Mean daily progeny was highest (12) on the first day, decreasing to zero after 20 days. Percent host parasitism was also highest on the first day (35%) decreasing to nearly 0% after 18 days. There appear to be three parasite larval instars. Host larvae often remained alive after parasite emergence.     

Development of the muscle system and contractile activity in the mussel Mytilus trossulus (Mollusca, Bivalvia)

The development of contractile apparatus was subjected to comparative analysis during ontogenesis of the mussel Mytilus trossulus. Indirect immunofluorescence with the polyclonal antibody against mussel twitchin, a protein of thick filaments, and florescent phalloidin as a marker of filamentous cell actin were used to monitor changes in the developing muscle system at different larval stages. The first definitive muscle structures were found at the late trochophore stage (36 h after fertilization) and starting from the midveliger stage (96 h), striated muscles, which are never present in adult mussels, were distinctly seen. The striated muscle periodicity was 1.25 microm in both mussle larvae and adult scallop. The contractile activities of veliger and adult muscles were measured using an electronic signal-processing videosystem. This work is the first complex study of morphological, biochemical, and physiological characteristics of the muscle system in the larvae and adult mollusks.     

Effects of Artificial Filamentous Substrate on Zebra Mussel (Dreissena polymorpha) Settlement

Though a great deal of research focuses on the range expansion and presence of adult zebra mussels, there is still a need to understand the processes of larval settlement and how that relates to adult populations. There is evidence that marine bivalves preferentially settle on filamentous substrates such as hydroid colonies and algae; however, similar studies are rare in freshwater systems. We examined the importance of filamentous substrate for the settlement of the zebra mussel (Dreissena polymorpha) larvae by deploying PVC settlement plates with and without polypropylene filaments in the Bark River for a 6-week period. Larval supply was monitored weekly. Our results suggest that artificial filaments facilitated recruitment, primarily by increasing surface area available for attachment. Mussels on artificial filaments were significantly smaller in size than mussels attached to filamentous or control plate surfaces, providing some evidence that mussels may detach from filamentous substrate after initial settlement. This study adds to our general understanding about the role of filamentous substrates in the process of larval settlement and suggests that substrates colonized by filamentous epibionts may face increased risk of fouling by zebra mussels. An erratum to this article is available at .     

Development of the muscle system and contractile activity in the mussel <Emphasis Type="Italic">Mytilus trossulus</Emphasis> (Mollusca,Bivalvia)

The development of contractile apparatus was subjected to comparative analysis during ontogenesis of the mussel Mytilus trossulus. Indirect immunofluorescence with the polyclonal antibody against mussel twitchin, a protein of thick filaments, and fluorescent phalloidin as a marker of filamentous cell actin were used to monitor changes in the developing muscle system at different larval stages. The first definitive muscle structures were found at the late trochophore stage (36 h after fertilization) and starting from the midveliger stage (96h), striated muscles, which are never present in adult mussels, were distinctly seen. The striated muscle periodicity was 1.25 μm in both mussel larvae and adult scallop. The contractile activities of veliger and adult muscles were measured using an electronic signal-processing video workstation. This work is the first complex study of morphological, biochemical, and physiological characteristics of the muscle system in the larvae and adult molluscs.     

Temporal and spatial variability in the heavy-metal content of Dreissena polymorpha (Pallas) (Mollusca: Bivalvia) from the Kleines Haff (northeastern Germany)

The present investigation was performed on zebra mussels, Dreissena polymorpha (Pallas), which were sampled from the Kleines Haff. As a part of the Oder estuary, the Kleines Haff acts as a sink for the load of the river Oder. Mussel shells and mussel tissue were analyzed for their content of selected heavy metals, based on the composition of the suspended matter. Mussels were sampled in May, July, August and September 1996 at different locations and divided into three groups regarding their body size. The data show that concentrations of lead, cadmium and mercury vary during the year. Mussel shells and mussel tissue showed seasonal and local differences in heavy-metal concentration. Between the size classes, however, there was no significant difference, with one exception: the lead content in tissues was significantly higher in large mussels (>2.5 cm shell length) than in small ones (<1.9 cm). The concentrations of lead and cadmium clearly decreased in mussel shells from May to September, while they increased in mussel tissues. The lead concentration in the tissue corresponded to that of mercury. The highest values measured for mercury were 218 μg/kg dry weight (DW), for cadmium 1030 μg/kg DW and for lead 6182 μg/kg DW. The average concentration of heavy metals in mussel tissue was 9 to nearly 170 times lower than in the surrounding sediment and seston. It can be assumed that a balance exists between the concentration of heavy metals in the mussels' food and the mussels themselves.     

Food selection of Tanytarsus gracilentus larvae (Diptera: Chironomidae): An analysis of instars and cohorts

Gut contents of the detritivorous Tanytarsus gracilentus larvae were studied at one site in Lake Myvatn, Iceland. Samples were collected with a sediment corer. Sediment samples were taken from the surface of the intact core before the larvae were collected. Gut contents were compared between different larval instars and cohorts, and to the surface sediment. The composition of the gut contents of all instars was different from that of the sediment surface. The first instar selected small diatoms of the genus Fragilaria, as single and paired cells, and the fourth instar selected detritus items of more variable size and origin. Apart from the third instar larvae, there were similar trends in food selectivity between the same instar of different cohorts. No major changes occurred in the composition of the surface sediment during the time of this study.     

First record of symphoresy between nymphs of the stonefly Kempnyia tijucana,and chironomid larvae,Nanocladius (Plecopteracoluthus) sp., in the Neotropics

The symphoretic relationship between a species of Nanocladius (Plecopteracoluthus) (Diptera, Chironomidae) and Kempnyia tijucana (Plecoptera, Perlidae) is recorded and described for the first time from southeastern Brazil. About 31% of the collected perlids were hosts of the chironomid larvae. The entire larval cycle of N. (Plecopteracoluthus) sp. may be completed on a single instar of K. tijucana and the larval position on the host varied according to the stage of development of the chironomid, apparently being constant for young and old instars.     

Interaction of Acronicta rumicis (Lepidoptera: Noctuidae) and its larval parasitoid, Glyptapanteles liparidis (Hymenoptera: Ichneumonidae)

As a result of parasitism by Glyptapanteles liparidis in the first, second, third and fourth instar larvae of Acronicta rumicis, the mortality of each larval stage was found to be 46.67, 90, 71 and 16.67%, respectively. The mortality was highest when G. liparidis parasitized the second and third instar larvae. The difference in mortality between the parasitized group and the control group was 72.14% in the second instar larvae. With regards to the food consumption of the parasitized larvae, the first and second instar larvae consumed 6495.58 ± 646.52 mm² (leaf surface) and 7951.12 ± 4167.36 mm², respectively, while the third and fourth larvae consumed 13 826.77 ± 3396.66 mm² and 18 599.85 mm², respectively, showing that food consumption increased with instar stages of the host larvae. The clutch size of G. liparidis increased in relation to the instar stages of the host: it was 25.25 ± 7.89, 48.65 ± 53.75, 91.09 ± 44.52 and 114 individuals when they were fed with the first, second, third and the fourth instar larvae of the host, respectively.     

Biology of epiphytic Chironomidae (Diptera:Nematocera) in chalk streams

Submerged macrophytes are a conspicuous feature of chalk stream ecosystems, supporting large populations of diatoms and invertebrates, including larvae of the nematocerous family Chironomidae. Close temporal and spatial association is evident between chironomid larvae and diatoms, and diatoms are frequently a major component of the food of midge larvae. Larvae provided with food that is rich in diatoms survive better and grow and develop more quickly than larvae that are supplied with food that is predominantly fine organic detritus. First instar larvae selectively feed on diatoms but it is likely that selection is on the basis of particle size, rather than for diatoms per se. Three species of epiphytic larvae (2 Cricotopus spp. and Eukiefferiella ilkleyensis) transfer to a diet that is predominantly of fresh plant material (Ranunculus calcareus leaves) in the third and fourth instar. The life cycle strategies of many species of Orthocladiinae equip them to exploit temporarily favourable environmental conditions very rapidly and effectively. This fact helps to explain the coexistence of species with similar strategies of resource utilization, as part of the normal epiphytic fauna of chalk streams.     

Influence of ecosystem engineers on ecosystem processes is mediated by lake sediment properties

Invasive species may impact biotic community structure, ecosystem processes, and associated goods and services. Their impact may be especially strong when they also serve as ecosystem engineers (i.e. organisms affecting the physical habitat and resources for other species). Dreissenid mussels fill both these roles, having invaded the Laurentian Great Lakes in the late 1980s, and also serve as ecosystem engineers by altering nutrient fluxes and influencing the microbial food web through direct nutrient release and excretion of feces and pseudo‐feces at the water–sediment interface. We conducted laboratory experiments to investigate how the different functional traits of invasive quagga mussels (filtering activity and direct nutrient release) and native chironomid larvae (tube building and bioirrigation) interact with lake sediment of differing organic matter content to influence biogeochemical fluxes and water quality. Our results showed that sediment reworking and ventilation activities by chironomid larvae increased oxygen penetration in the sediment, affecting primarily pore water chemistry, whereas invasive mussels enhanced nutrient releases in the surface water. However, sediment organic matter modulated the effects of ecosystem engineers on system‐level processes; chironomids had a greater influence on sediment reworking and microbial‐mediated processes in organic‐rich sediments, whereas quagga mussels enhanced nutrient concentrations in the overlying water of organic‐poor sediments. These results have management implications, as the effects of invasive mussels on the biogeochemical functioning in the Great Lakes region and elsewhere can alter system bioenergetics and promote harmful algal blooms.     

Field and laboratory studies of Ophryoglena sp. (Ciliata: Ophryoglenidae) infection in zebra mussels,Dreissena polymorpha (Bivalvia: Dreissenidae)

This study, conducted in the Dnieper-Bug Canal in Belarus, is the first to monitor the seasonal (June-November) dynamics of infection with the parasitic ciliate Ophryoglena sp. in a zebra mussel (Dreissena polymorpha) population. Mean population prevalence and intensity of infection varied, respectively, from 11 to 62% and from 0.9 to 24.1 ciliates/mussel. Mean prevalence was highly correlated with mussel length in mussels <20 mm (R(2)=0.97) and was lower in larger mussels. Mean infection intensity in mussels 1-25 mm long was similarly correlated with their size (R=0.98), reached a maximum in the 20-25 mm size-class, and then sharply decreased, thus providing evidence, albeit limited, that high intensity of infection might be lethal. Transinfection of zebra mussels by Ophryoglena sp. was achieved in the laboratory-a first for a protozoan parasite of D. polymorpha; from an initial complete lack of infection, mean prevalence and intensity rose, respectively, to 86.7% and 8.3 ciliates/mussel.