Unionid growth patterns in rivers of differing riparian vegetation

1. Growth rates were examined as potential controlling agents of unionid distributions.
2. Analyses of long-term growth in unionid shells revealed two distinct patterns. Species which dominate rivers with forested riparian vegetation (e.g. Elliptio dilatata ) show slow growth throughout life, whereas species which dominate grassy rivers (e.g. Pyganodon grandis ) show rapid growth during early life and achieve a smaller maximum size at a younger age.
3.  Pyganodon grandis , which occurs in both river types but is much more abundant in grassy habitats, demonstrates a single growth pattern in both basin types. In contrast, Lasmigona complanata (Barnes, 1823), which occurs equally in both basin types, demonstrates two growth patterns which differ depending upon which river is inhabited. In forested rivers, L . complanata grow slow and steady, whereas in grassy rivers, these unionids grow faster and achieve maximum size earlier.
4. Short-term transplant studies of P . grandis and E . dilatata confirmed this pattern of growth for specialist species.     

The parasite-host relationships between the glochidia of the European pearl oyster Margaritifera margaritifera (Margaritiferidae: Bivalvia) and mass fish species in the European north of the USSR

Narrow specificity of larvae (glochidia) of Margaritifera margaritifera to salmon in the rivers of the Kola Peninsula was proved experimentally. It was found that in the gills of minnow, the other mass fish in the northern rivers of the USSR, larvae of M. margaritifera cannot develop and perish. Reasons causing the narrow specificity of M. margaritifera to Salmonidae are discussed.     

Intra- and interspecific agonistic behavior of the subterranean termite Microcerotermes crassus (Isoptera: Termitidae)

The aim of our study was to investigate the intra- and interspecific agonistic behaviors exhibited by the worker and soldier castes of the subterranean termite Microcerotermes crassus Snyder (Isoptera: Termitidae). Aggression between M. crassus colonies from different field locations and also against three termite species--Coptotermes gestroi (Wasmann), Globitermnes sulphureus Haviland, and Odontotermes sp.--were observed in the laboratory. Termite responses were tested in paired combination of castes (soldiers versus soldiers, soldiers versus workers, and workers versus workers) consisting of 10 individuals each. Significant agonistic behaviors were observed only in encounters between pairings of different termite species. M. crassus was aggressive toward individuals from different species but not toward individuals from different M. crassus colonies. Mortality of M. crassus reached 100% in most of the interspecific encounters. However, no or low mortality was recorded in the intraspecific pairings.     

Coping with warmer, large rivers: a field experiment on potential range expansion of northern quagga mussels (Dreissena bugensis)

SUMMARY 1. Zebra mussels ( Dreissena polymorpha ) have established a much greater range in North America and Europe than quagga mussels ( D. bugensis ), which occupy a very similar niche.
2. We hypothesised that quaggas are physiologically capable of sustaining populations in warmer rivers currently occupied only by zebra mussels and that unidentified, non-physiological factors account for their more limited distribution.
3. Growth and survival of individually tagged mussels (976 D. bugensis from Lake Erie; 2625 D. polymorpha from Lake Erie and the Ohio River) were recorded monthly for up to 15 months in an outdoor stream mesocosm receiving unfiltered water from the Ohio River.
4. Extreme temperatures stressed both species; but in contrast to several previous laboratory studies, quaggas survived high temperatures better than zebra mussels. We suspect this was the result of species-specific differences in their ability to obtain, assimilate and/or catabolise food at high, sublethal temperatures.
5. A unimodal growth pattern was observed in both species, with the highest growth rates from late spring to early autumn.
6. Our survival and growth data suggest that quaggas are not physiologically limited from expanding southward.
7. While lacking definitive proof that dreissenid populations in rivers are ecologically sustainable without upstream lentic ecosystems and/or unintended human intervention, we suggest that complex river currents and upstream retentive and highly productive slackwater habitats in rivers may help sustain downstream populations of these meroplanktonic, dreissenid mussels.     

Energetically costly behaviour and the evolution of resting metabolic rate in insects

1. A general hypothesis is presented to explain interspecific differences in size-independent resting metabolic rate. This hypothesis is based on a presumed trade-off between a low resting metabolism and adaptations of metabolism during activity.
2. With such a trade-off, selection to reduce resting metabolism is less intense in active species than in species where resting metabolism constitutes a large proportion of the daily metabolic costs. Those animals that spend more energy on activity should therefore have a higher resting metabolic rate than animals that spend less energy on activity.
3. A literature review reveals that flying insects have higher resting metabolic rates than species that use energetically less demanding types of locomotion.
4. Insects producing acoustic advertisement signals can be shown to have higher mass-independent resting metabolic rates than closely related species without this energetically demanding behaviour.
5. Literature data on vertebrate resting metabolic rates are also consistent with the presented hypothesis: the more energy animals spend on activity, the higher the mass-independent resting metabolic rate.     

Zebra Mussel Infestation of Unionid Bivalves (Unionidae) in North America

SYNOPSIS. In 1989, zebra mussels received national attentionin North America when they reached densities exceeding 750,000/m2in a water withdrawal facility along the shore of western LakeErie of the Laurentian Great Lakes. Although water withdrawalproblems caused by zebra mussels have been of immediate concern,ecological impacts attributed to mussels are likely to be themore important long-term issue for surface waters in North America.To date, the epizoic colonization (i.e., infestation) of unionidbivalve mollusks by zebra mussels has caused the most directand severe ecological impact. Infestation of and resulting impactscaused by zebra mussels on unionids in the Great Lakes beganin 1988. By 1990, mortality of unionids was occurring at somelocations; by 1991, extant populations of unionids in westernLake Erie were nearly extirpated; by 1992, unionid populationsin the southern half of Lake St. Clair were extirpated; by 1993,unionids in widely separated geographic areas of the Great Lakesand the Mississippi River showed high mortality due to musselinfestation. All infested unionid species in the Great Lakes(23) have become infested and exhibited mortality within twoto four years after heavy infestation began. Data indicate thatmean zebra mussel densities >5,000–6,000/m² and infestationintensities >100-200/unionid in the presence of heavy zebramussel recruitment results in near total mortality of unionids.At present, all unionid species in rivers, streams, and akesthat sympatrically occur with zebra mussels have been infestedand, in many locations, negatively impacted by zebra mussels.We do not know the potential consequences of infestation onthe 297 unionid species found in North America, but believezebra mussels pose an immediate threat to the abundance anddiversity of unionids.     

Aspects of the ecology and natural history of Paraergasilus rylovi (Copepoda, Ergasilidae) parasitic in unionids of Finland

The distribution of Paraergasilus rylovi in 17 populations of unionids was investigated. In 1 unionid population, the parasite was studied regarding host age, size, sex, and the reproductive period (occurrence of egg sacs). Results from pooled material from the years 1987--1989 and 1996 (southern Finland, 11 populations) indicated that Anodonta piscinalis (n = 1,359) is the main host (total mean prevalence 71% and intensity +/-SE of infection 16.4+/-0.6). Pseudanodonta complanata (n = 106) was infected occasionally (3% and 1.3+/-0.3), whereas Unio pictorum (n = 108) and U. tumidus (n = 17) were not infected. Results from 17 A. piscinalis populations showed that P. rylovi occurs in southern Finland but not in northern Finland. In A. piscinalis, the mean intensity of infection was higher in lake populations than in river populations. Both host age and length had a negative relationship with the intensity of P. rylovi infection. Host sex did not affect the intensity of infection. Egg sacs of P. rylovi were found from June to August. There was a tendency for higher intensities of infection in autumn. Infection by the digenean Rhipidocotyle fennica had no effect on the intensity of P. rylovi infection.     

The influence of food competition and host specificity on the transmission of Triaenophorus crassus (Cestoda) and Cystidicola farionis (Nematoda) to Coregonus lavaretus and Coregonus albula (Pisces:Coregonidae) in Finland

As a superior competitor for planktonic food, vendace (Coregonus albula), when abundant, is expected to displace whitefish (Coregonus lavaretus) from feeding on plankton and to force it to rely more on benthic food. The predicted result would be a reduced abundance of the copepod-transmitted cestode Triaenophorus crassus in whitefish, but an increase in the abundance of the nematode Cystidicola farionis transmitted via benthic amphipods. We studied the occurrence of both parasites in whitefish during 1991-1996 in three interconnected areas at Lake Saimaa, Finland, where the densities of the vendace stocks varied due to natural fluctuation in year-class strengths. In accordance with our hypothesis, some indication of the effect of the density of the vendace population on abundance of C. farionis infection in whitefish was found, but not in the case of T. crassus. Only 0.2% of vendace were infected with T. crassus, while up to 100% of the whitefish in the yearly samples harboured the parasite. In further experiments we clarified which copepod species in Lake Saimaa act as first intermediate hosts of T. crassus, and verified from stomach samples the exposure of both whitefish and vendace to those species. Experimental infections indicated that the infectivity of T. crassus is lower for vendace than for whitefish. We suggest that the reason why vendace stock density does not affect T. crassus infection in whitefish is that T. crassus is transmitted in littoral areas during a short period in spring. At that time of the year copepods are abundant and available to both whitefish and vendace, but since the parasite is less infective to vendace. they do not become infected. At other times of the year, dense vendace stocks may force whitefish to shift to benthic food, which includes amphipods transmitting C. farionis. During vendace stock decline, whitefish may, however, continue to feed on plankton and avoid exposure to C. farionis.     

Freshwater Pearl mussels of the genus Margaritifera (Mollusca: Bivalvia) described as M. elongata (Lamarck, 1819) and M. borealis (Westerlund, 1871) should be classified with M. margaritifera (Linnaeus, 1758)

The shells of Pearl mussels from the basins of the Solza, Keret’, and Umba rivers flowing into the White Sea have been measured to determine the ratio of shell convexity to its maximum height. This ratio is the main character that, according to Bogatov et al. (2003), allows one to distinguish between three species of the genus Margaritifera: M. margaritifera, M. elongata, and M. borealis. It has been found that the above ratio gradually increases as the shell grows. Therefore, this character is unsuitable for species diagnosis, the more so that no hiatus in it between the three forms of pearl mussels has been revealed in any of the samples studied. On this basis, it may be concluded that Northern Europe, including Russia, is inhabited by only one species of pearl mussels, M. margaritifera.     

Differing effects of suspended sediments on the performance of native and exotic Daphnia

1. Although large cladocerans are usually uncommon in large rivers, Daphnia lumholtzi (an exotic species in North America) is widespread and occasionally abundant. We collected zooplankton on the Illinois River (Illinois, U.S.A.) in 1995 and 1996 and found that the peak density of D. lumholtzi (25 L⁻¹) typically exceeded that of all native species combined. Maximum density occurred during warm periods (up to 27 °C) when concentrations of inorganic suspended sediments were high (>50 mg L⁻¹).
2. Using a life table experiment, we examined the effects of variation in suspended sediment (0 and 80 mg L⁻¹) and food (10⁴ and 10⁵ Ankistrodesmus cells mL⁻¹) on fitness of D. lumholtzi and the native Daphnia parvula. Daphnia lumholtzi had greater survivorship than D. parvula in most treatments and higher life-time fertility than D. parvula in all treatments. Both species achieved their fastest intrinsic rates of growth in treatments with high food, but their responses to suspended solids differed. The growth rate of D. lumholtzi in high food was slightly increased by higher turbidity, whereas that of D. parvula was depressed.
3. Results suggest that the ability of D. lumholtzi to tolerate suspended solids is an important factor contributing to its success in invading North American rivers.     

Evidence for a negative fitness-density relationship between parent density and offspring quality for two Xenopsylla spp. parasitic on desert mammals

We tested the hypothesis of negative fitness-density relationships and predicted that an increase in the density of parent fleas would result in lower survival rates and longer development time of pre-imagoes as well as shorter time to death from starvation of newly emerged imagoes. These predictions were experimentally tested on Xenopsylla conformis Wagner and Xenopsylla ramesis Rothschild feeding on two rodent species, Meriones crassus Sundevall or Dipodillus dasyurus Wagner. Survival of larvae and pupae, but not eggs, was negatively affected by parent density. An increase in parent density led to a decrease in the number of imagoes of the next generation. Eggs of both species developed faster when the parents were at low densities on either host. The same was true for larval X. ramesis, but not larval X. conformis. The negative effects of parent density on the duration of pupal development were evident in X. conformis, parents of which fed on both hosts, and X. ramesis from parents fed on M. crassus, whereas X. ramesis from parents fed on D. dasyurus developed faster at low densities. A negative effect of density on the development of offspring from egg to imago in X. conformis was manifested mainly when parent fleas fed on D. dasyurus, whereas the negative effect of density on offspring development in X. ramesis was manifested mainly when parent fleas fed on M. crassus. Although there was no general effect of parent density on the resistance of imago offspring to starvation, male X. ramesis from parents fed at the highest density survived starvation for significantly shorter times compared with those from parents fed at lower densities. Manifestation of the negative effect of parent density on offspring quality appears to vary with flea species and may be affected by host species.     

The influence of temperature and fine-scale resource distribution on resource sharing and domination in an ant community

Abstract.  1. In order to coexist in sympatry, subordinate species must somehow obtain resources that dominant taxa may generally control. This study examines the response of an ant community to fine-scale variation in resource distribution, as a mechanism enabling resource acquisition by subordinates in the presence of dominant taxa. Food (6 g) was portioned as one, eight, or 64 items in a 0.4-m² area, centred on nests of Monomorium sydneyense Forel, considered the most dominant ant in the area. This ant is a newly established exotic species in our study site of Tauranga, New Zealand.
2. As the number of food items increased, a significant increase in the number of species utilising the food was observed, associated with an increase in the non-utilised proportion of food items.
3. The changing occupation rates of food items by M. sydneyense and three other species were modelled against soil surface temperature and the varying dispersion rates of the food resource. Significant main effects of food density, site, species, and temperature were observed on the probability of food being occupied by a species. However, there were also significant interaction effects, making it impossible to interpret the main effects in isolation. Monomorium sydneyense dominated a smaller proportion of resources in trials with increased resource distribution and cooler temperatures, allowing more species to access resources.
4. There was considerable variation between species in their responses to variation in temperature and food distribution. Although most species were able to respond to increasing resource dispersion, species that were in low abundance apparently could not. However, even species that could respond to increasing resource dispersion were limited in the number of resources they could secure.     

Resource partitioning between unionid mussels in a Swedish lake outlet

Partitioning of food and space resources of two dominating unionid mussel species, Anodonta piscinalis and Unio pictorum , was investigated in a South Swedish lake outlet. Differences in diurnal activities were not considered to be a mechanism for niche segregation. The two species ingested particles of almost identical size distribution indicating a high overlap in food. Mussel distribution was correlated to environmental variables including substrate properties, water depth, current velocity, and distance from the lake, the latter being a relative measure of food quality and quantity, U. pictorum dominated near the lake and in the centre of the river while A. piscinalis had its peak density ca. 500 m below the lake and was relatively more abundant along the river margins. At maximum mussel densities, which were found near the lake, a separation in space was more obvious than downstream, implying possible interspecific interactions.     

Predator–prey instability: individual-level mechanisms for population-level results

1. In previous work we established that increasing temperature led to a destabilization of the population dynamics of the invertebrate carnivore Mesostoma ehrenbergii and its prey Daphnia pulex , which ultimately resulted in the local extinction of Daphnia at higher temperatures. Two mechanisms are proposed to explain the population-level phenomena: (1) quantitative changes in carnivore vital rates with increasing temperature led to stronger functional and numerical response and (2) qualitative changes in the dynamic allocation of energy to reproduction by the predator with increasing temperature introduces inverse density dependence in the predator's response.
2. The growth of individual M. ehrenbergii was monitored under various food conditions to determine the effect of two temperatures (18 and 24 °C) and five food levels on rates of growth, prey consumption and reproduction and on reproductive allocation patterns.
3. The first mechanism was supported by both higher consumption rates (stronger functional response) and faster growth rates with earlier age at maturity and shorter generation time (stronger numerical response).
4. Evidence for mechanism two was also provided by an alteration of the reproductive allocation pattern with temperature. Viviparous (subitaneous) eggs were more likely to be produced by this carnivore at low food levels at 24 °C, while at 18 °C, high food levels were required before individuals made this switch. This shift actually introduces inverse density dependence in the predator's numerical response which is highly destabilizing.
5. Based on the results of this study, the differential effect of M. ehrenbergii on the dynamics and structure of its D. pulex prey populations can be attributed to changes in both physiological rates and reproductive allocation patterns with temperature.     

The endangered thick-shelled river mussel (<Emphasis Type="Italic">Unio crassus</Emphasis>): a new host species for the European bitterling (<Emphasis Type="Italic">Rhodeus amarus</Emphasis>)

Large freshwater mussels (Unionoida) are declining throughout the world. The European bitterling Rhodeus amarus (Bloch, 1782) female spawns its eggs inside the unionids’ shells, where fertilisation and further embryonic development take place; thus its reproduction depends fully on the presence of large freshwater mussels. Unio crassus, previously regarded as one of the most numerous unionids in Europe, is now listed in the IUCN Red Data List as being globally endangered. Despite its previous prevalence, it was never reported as a host for the bitterling. A large population of U. crassus was studied in small river at the ?wi?tokrzyskie Mts (Poland), where also electrofishing was conducted. In each bitterling territory located on the study plots, we found individuals of U. crassus, with the bitterling eggs or larvae developing on mussel’s gills. That proves that this species can be also used by the bitterling for reproduction. We suggest that this relationship has not been reported to date due to the mussels’ rarity and ongoing decline. However, it is also possible that the endangered mussel is a novel host for the bitterling, which is expanding its range throughout Europe.     

Modelling interactions of food quality and quantity in homeostatic consumers

1. Boundaries between growth limitation by carbon (C) and phosphorus (P) in homeostatic heterotrophic consumers such as zooplankton will vary as demands on these two elements vary, as they should at different food quantities. At very low food quantity when production is close to zero, metabolic requirements (for carbon) become more important than growth requirements (for carbon and phosphorus in fixed proportion). Thus, the boundary separating C-and P-limited growth should be at a higher C : P ratio at low food quantity than at high food quantity.
2. A model including both metabolism and growth indicates that consumer growth should differ between foods of high vs. low phosphorus concentration only when food quantity is above a certain level. Thus, two foods might give identical consumer growth rates at low food quantity but give different consumer growth at higher quantity.
3. Solution of the model using parameters based on 2 mm Daphnia compared with a survey of C and P in seston of marine and freshwater sites supports earlier conclusions of the potential importance of food quality constraints on Daphnia growth.     

Demographic responses of adult Mesocyclops thermocyclopoides (Copepoda, Cyclopoida) to different plant and animal diets

1. We studied the effects of food type on adult females of the cyclopoid copepod Mesocyclops thermocyclopoides.
2. The test diets, covering a size range of 5–1250 μm, included a toxic strain of Microcystis aeruginosa , three algae (i.e. Chlorella vulgaris, Scenedesmus acutus and Chlorogonium elongatum ), three ciliates (i.e. Tetrahymena pyriformis, Stylonychia notophora and S. mytilus ), two rotifers (i.e. Brachionus angularis and B. calyciflorus ) and two cladocerans (i.e. Ceriodaphnia cornuta and Moina macrocopa ), and a selected subset of them in a second experiment.
3. Experimental diets were started with the last juvenile instar (C5) and data were collected on the newly moulted adult females. The survival of the copepod was less affected by food type than its reproductive output. Net reproductive rate was significantly higher with animal than with plant food. Algal diets enriched with organic extracts supported higher reproductive rates than unenriched diets of the same algal species. The large and motile alga Chlorogonium gave performances which approached those of ciliate diets.
4. The pre-reproductive period of M. thermocyclopoides was shorter and its post-reproductive period longer with animal than with plant diets, the latter being chiefly caused by a briefer period between clutches.
5. The frequency of infertile clutches increased in later clutches, indicating possible sperm limitation in females which have mated only once.
6. There was a significant, positive correlation between the size of food particles and the lifetime reproductive output of M. thermocyclopoides , with more than an order of magnitude difference in the total fecundity between the largest and the smallest food items.
7. Mesocyclops thermocyclopoides achieved the highest total fecundity with 'mixed' food, and thus, reflected the adaptive value of omnivory for this species.     

Xantusiid lizards have low energy, water, and food requirements

Lizards in the family Xantusiidae (the night lizards) are known to have resting metabolic rates that are only half those of other lizards of comparable size. We evaluated whether xantusiids also have low field metabolic rates (FMR) and food requirements by measuring FMR and water flux rates with doubly labeled water in three xantusiid species in their natural habitats. Free-living Xantusia vigilis, Xantusia henshawi, and Xantusia riversiana processed energy and water very slowly, about one-third as fast as do other reptiles of similar size. Xantusiid lizards have a distinctive life history that is characterized by very slow growth and low reproductive rates, and they are intensely reclusive. This general lifestyle is also found in some species that live in environments with scarce food resources, such as in caves and in arid habitats, and these species may also have relatively low energy requirements.     

Evaluation of ITS rDNA as a complement to mitochondrial gene sequences for phylogenetic studies in freshwater mussels: an example using Unionidae from north-western Europe

Mitochondrial inheritance in the Unionidae is complex since mitochondria can be inherited from both parents. An increased rate of recombination could lead to erroneous homology assessments, which could cause problems for phylogenetic reconstruction. For this reason we investigated the possibility of using a nuclear marker, the ribosomal internal transcribed spacer region, for phylogenetic studies in the Unionidae, as a complement and comparison to two of the most widely used mitochondrial genes today. The nuclear ribosomal internal transcribed spacer region ( ITS1 , 5.8S , ITS2 ) was sequenced from 72 specimens representing six of the seven species of Unionidae mussels occurring in NW Europe: Unio pictorum , U. tumidus , U. crassus , Anodonta anatina , A. cygnea and Pseudanodonta complanata. Sequences from Margaritifera margaritifera were used as an outgroup . The ITS sequences of all species were found to have low intragenomic and infraspecific variation. Compared to mitochondrial genes ( 16S and COI ) they show an intermediate genetic diversity. Phylogenetic analyses produce tree topologies that are congruent with those resulting from analyses of the mitochondrial sequences. Likewise, an incongruence length difference (ILD) test showed no significant incongruence between data sets, indicating that if recombination has occurred it has not produced any conflicting patterns. Best-resolved and supported trees are obtained when gaps are treated as a fifth character state. A combined analysis of the three gene regions shows that Unio crassus and U. pictorum are more closely related than either to U. tumidus . Pseudanodonta is nested within Anodonta as sister taxon to A. cygnea . Advice on how to best preserve mussel material for DNA studies is provided.