Countering morphological ambiguities: development of a PCR assay to assist the identification of <Emphasis Type="Italic">Tubifex tubifex</Emphasis> oligochaetes

The freshwater oligochaete, Tubifex tubifex, is a common resident of organic-rich sediments worldwide. Although it is a familiar species to fish enthusiasts, toxicologists and parasitologists, T. tubifex often confounds definitive identification due to the similarity that immature specimens bear to several other common oligochaetes, and given the degree of plasticity of key morphological characters due to environmental conditions and/or age of specimen. To solve this identity crisis, we used a polymerase chain reaction based molecular approach and developed a T. tubifex specific assay with primers that amplify a 192 bp fragment of the internal transcribed spacer region 1 ribosomal DNA. We tested these primers on four T. tubifex mitochondrial genotypes, and on other oligochaete species from nine genera. The primers amplified all specimens identified morphologically asT. tubifex. They did not amplify any other species, including morphologically similar worms possessing hair chaetae (Dero digitata, Ilyodrilus templetoni, Tubifex ignotus or Rhyacodrilus spp.) or other oligochaetes often found with T. tubifex (Lumbriculus variegates, Limnodrilus hoffmeisteri, Stylodrilus heringianus or Trichodrilus sp.). This technique should remove the uncertainties all too often associated with identification of T. tubifex.     

A comparison of two tubificid oligochaete species as candidates for sublethal bioassay tests relevant to subtropical and tropical regions

Two tubificid oligochaetes, Branchiura sowerbyi and Tubifex tubifex, were evaluated as potential test organisms for sediment bioassays. We attempt to reproduce the sediment bioassay proposed by Reynoldson et al. (1991) using his strain of Tubifex tubifex and his reference sediment and to compare this technique using Branchiura sowerbyi. This species was chosen because it is more common and dominant in tropical and subtropical environments than Tubifex tubifex. Data on survival and reproduction were obtained for both species, and growth estimates were obtained for B. sowerbyi. The sublethal bioassay with T. tubifex confirmed earlier estimates of a test duration of 4 weeks at 22.5 °C. B. sowerbyi cultures can produce usable estimates in 21 days at 30 °C.     

Host–parasite interactions and competition between tubificid species in a benthic community

1. Parasites can be important determinants of host community structure while host community structure can influence the success of parasites, although both are often overlooked. In two laboratory experiments, we examined interactions among Myxobolus cerebralis syn Myxosoma cerebralis Höfer, the myxozoan parasite that causes salmonid whirling disease, and two coexisting tubificid species: Tubifex tubifex (Müller), which is the alternate host of the parasite, and Limnodrilus hoffmeisteri Claparède, which is not susceptible. In the first experiment, we examined T. tubifex infection prevalence when exposed to nine doses of spores. In the second experiment, we examined tubificid and parasite success under three spore doses when tubificids were combined in a response surface experimental design used to detect interactions among species. 2. The outcomes of interactions between tubificid species were complex. The number and biomass of offspring of both tubificid species were density dependent when in monoculture or in combination with the other species. Adult growth of T. tubifex was also density dependent in monoculture, but when L. hoffmeisteri replaced one‐half of the T. tubifex in the high‐density treatment, adult growth of T. tubifex was higher than in monoculture. Adult growth of L. hoffmeisteri was always density independent. Whether T. tubifex was exposed to the parasite or not did not change the outcome of these interactions. However, adult growth of T. tubifex, but not L. hoffmeisteri, was highest when M. cerebralis was present. 3. Infection prevalence of T. tubifex increased with increasing spore dose. Infection prevalence was lowest in the high‐density T. tubifex monoculture and highest in the low‐density T. tubifex monoculture and when T. tubifex was in combination with L. hoffmeisteri. 4. Both intraspecific and interspecific competition influenced tubificid success, but T. tubifex gained some competitive advantage through increased adult growth when in combination with L. hoffmeisteri. Whether T. tubifex was exposed to the parasite or not did not change the outcome of the interactions between the tubificid species. 5. The presence of L. hoffmeisteri did not decrease the prevalence of infection in T. tubifex, suggesting that parasite success was unaltered by the presence of this non‐susceptible species.     

Cyst formation of Tubifex tubifex (Müller) — an adaptation to survive food deficiency and drought

Adult individuals of Tubifex tubifex (Müller) (Oligochaeta, Tubificidae) could be induced to form cysts in the laboratory. Hiding in cysts, Tubifex tubifex survived a five-month drought period in the field. Encysted Tubifex tubifex had a lower super-cooling-point than mobile individuals. Food shortage is believed to be the main factor in cyst formation.     

The biology of Oligochaeta from Dorset chalk streams

Fewer species and more individuals of Tubificidae were present in the soft sediments of a polluted ditch than in the relatively unpolluted Bere Stream. Changes in width frequency of natural populations of Tubifex tubifex and Limno-drilus hoffmeisteri throughout the year were similar at both the sites investigated. In laboratory experiments larger populations of Tubifex tubifex developed in fine sediments than coarse. By means of a width-dry-weight relationship it was possible to estimate the weight of the experimental populations.     

The ecology of some Benthic Oligochaeta from the Paraná River,Argentina

Simple and multiple correlations among physical and chemical parameters and densities of the dominant Oligochaete species were calculated for various channels of the middle Paraná valley and its tributaries. Paranadrilus descolei Gavrilov, 1955, was observed in rivers with average depth and current velocity, mud-clay sediments, and low conductivity. Tubifex tubifex f. blanchardi Vejd., 1891, was found in channels of low depth, current velocity and discharge but with high conductivity. Limnodrilus hoffmeisteri Claparède, 1862, and Aulodrilus pigueti Kowalewski, 1914, were ubiquitous species. Narapa bonettoi Righi and Varela, 1983, was typical of rivers highest in depth, current velocity, and discharge with sandy sediments and low conductivity.     

Propagation of the myxozoan parasite Myxobolus cerebralis by different geographic and genetic populations of Tubifex tubifex: An Oregon perspective

Tubifex tubifex are obligate invertebrate hosts in the life cycle of Myxobolus cerebralis, the myxozoan parasite that causes whirling disease in salmonid fishes. This exotic parasite is established to varying degrees across Oregon’s Columbia River system (Pacific Northwest, USA) and characteristics of local T. tubifex populations likely play a role in the pattern of disease occurrence. To better understand these patterns, we collected T. tubifex from three Oregon river basins (Willamette, Deschutes, and Grande Ronde), determined their genotype (mitochondrial 16S rDNA lineage and RAPD genotype) and exposed 10 different populations to M. cerebralis in the laboratory. Four mt lineages were identified: I, III, V and VI. Lineage III was found in all river basins but dominated both central and eastern sites. The RAPD assay further divided these lineages into geographic sub-populations; no RAPD genotype was common to all basins. There was a significant difference in prevalence of infection and level of parasite production among the populations we exposed to M. cerebralis that was attributed to genotypic composition. Only lineage III worms released actinospores and only populations dominated by this lineage amplified the parasite. These populations had the lowest survival, however, the lineage dominant before exposure remained dominant despite the high prevalence of infection. The distribution and infection dynamics of susceptible T. tubifex throughout Oregon may contribute to the differences in M. cerebralis occurrence; our studies further support the influence of oligochaete genotypes on the manifestation of whirling disease in salmonid populations.     

Observations on cohorts of Tubifex tubifex cultured at different food levels,using cellulose substrate

In order to clarify the relationship between food availability and population dynamics in aquatic oligochaetes, short term cultures and cohort cultures of Tubifex tubifex were reared using substrates with different food concentrations, obtained by mixing sand with different amounts of cellulose powder.In short term experiments, T. tubifex seemed capable of utilizing cellulose substrates for growth or egg production. Yet, in the cohort experiment, newly hatched worms could not grow on cellulose substrates. Survivorship, however, appears to be influenced by cellulose concentration giving an indication that this material, although inadequate, is somehow utilized.     

Growth of Tubifex tubifex Müller (Oligochaeta,Tubificidae) under Various Trophic Conditions

Growth of Tubifex tubifex on highly caloric activated sludge and poor in organic matter natural silt was experimentally studied. The relationship between oxygen consumption rate, weight, and caloric value of T. tubifex body in culture on activated sludge was determined to calculate the growth efficiency (K₂ = P/P + R). The growth rate has been determined, and models of T. tubifex growth are given under various trophic conditions conforming to results of the experiment. Somatic growth, generative growth and life span of this species were compared on the basis of the experiments and literature. Acceleration of growth and prolongation of life under conditions of caloric food and delay of these processes in silt poor in organic matter have been established and measured. T. tubifex was found to have advantages as compared to other tubificid species in response to increasing amounts of nutrient food in waters polluted by organic matter and, therefore, to produce abundant populations under these conditions.     

Expression pattern of annelid <Emphasis Type="Italic">Zic</Emphasis> in embryonic development of the oligochaete <Emphasis Type="Italic">Tubifex tubifex</Emphasis>

Embryonic expression of a Zic homologue (Ttu-Zic) was examined in the oligochaete annelid Tubifex tubifex. The body plan of T. tubifex is characterized by obvious segmentation in the ectoderm and mesoderm. Ttu-Zic expression is detected in the mesodermal germ band and a subset of micromere descendants. Ttu-Zic is transiently expressed in primary m-blast cells (i.e., founder cells of mesodermal segments) as early as the time of their birth from M teloblasts. During its development, each mesodermal segment experiences two additional phases of Ttu-Zic expression. Ttu-Zic expression in micromere descendants is seen on the anterior surfaces of embryos undergoing teloblastogenesis; subsequently, these cells proliferate to form bilateral clusters, which then become internalized. Finally, clusters of Ttu-Zic-expressing cells are found in the center of the prostomium, corresponding to the cerebral ganglion. The Ttu-Zic expression profile in the early embryogenesis of T. tubifex may be homologous to those of evolutionarily distant animals.     

Production and population dynamics of Tubifex tubifex in the profundal zone of a freshwater reservoir in N. Italy

During a study of a pumped storage system from May 1979–June 1980 the profundal macrobenthos of the upper reservoir (Lago di S. Maria Valvestino) was sampled at a fixed station and the population of the tubificid Tubifex tubifex studied in detail. Eggs, embryos and the individuals living in an extra-cocoon stage were counted and individually weighed from monthly samples, according to the methods described in Bonomi & Di Cola (1980). Numerical recruitment during the study period was estimated as 257 000 ind m^–2 yr^–1; of which 110 000 died either as eggs or as embryos, i.e. inside the cocoons, and a further 128 000 died before they attained sexual maturation. The data seem to confirm the typical demographic strategy of T. tubifex i.e. high fecundity and high mortality in the early life stages. The total annual production of the species was estimated at 91.7 g (w.w.) m^–2. The low P/B ratio (2.0 yr^–1) is considered to be mainly due to high population densities.     

The importance of worm identity and life history in determining the vertical distribution of tubificids (Oligochaeta) in a riverine mud

The vertical distribution of Tubifex tubifex, Limnodrilus hoffmeisteri and L. udekemianus, in a riverine mud was studied over a year. Distribution was dependent upon species identity, season and locality. The size structure of the population, and hence species life history, was of fundamental importance in determining temporal patterns of vertical distribution. A positive correlation between worm length and depth of penetration was clearly demonstrated for all three species. However, the mid-stream populations of the three species were closer to the mud surface during the summer and autumn than were the near-bank populations, although the size structures of the populations were not significantly different. Thus, another factor, possibly the distribution of food, also influenced the vertical distribution of the worms. Cocoon distribution was similar to that of the adult worms. Cocoons of the larger species, L. udekemianus, occurred deeper in the mud than those of T. tubifex. A comparison between the vertical distributions of tubificids in cores sectioned in situ, on the stream bank, and 30 mins later, showed there to be no significant change in distribution with time.     

Hair today,gone tomorrow: induced chaetal changes in tubificid oligochaetes

Laboratory experiments were conducted to determine the extent of chaetal variation in the tubificids Tubifex tubifex and Ilyodrilus frantzi and the naidids Specaria fraseri and Nais communis under varying environmental conditions. Univariate exposures were carried out using different levels of pH, salinity, water hardness and mercury. We were not able to induce chaetal changes in the two naidids tested. However, we were able to reduce the hairs and pectinations of T. tubifex with exposure to pH, salinity and to hard water such that the bergi form was produced. Prolonged exposure to low or high pH resulted in the total loss of hairs and pectinates such that the blanchardi form was produced. We were able to eliminate the hairs and pectinates of I. frantzi (capillatus) in soft, freshwater exposures such that the bifidus form of I. frantzi was produced. Conversely, in hard or saline water we were able to induce formation of hairs and pectinates on the bifidus form such that the capillatus form was produced. These changes occurred at time intervals ranging from a few days to two months.     

Some characteristics of genetic variants of Tubifex tubifex (Müller, 1774) (Oligochaeta: Tubificidae) in laboratory cultures

Genetic variants of the oligochaete Tubifex tubifex were identified with enzyme electrophoresis and subsequently reared in laboratory cultures. Three types are abundant in field populations. Individuals that show homozygotic bands of glucosephosphate-isomerase (GPI) 22 together with isocitrate-dehydrogenase (IDH) 35 were labeled Type A. Type B is characterized by GPI 23 together with IDH 11 and Type C is characterized by GPI 11 with either IDH 34 or IDH 33. Initial results on freshweights of adults and cocoon production revealed differences between the two main types, A and B. In the same period, Type B reached higher weights and produced five times as many cocoons as Type A, whereas number of eggs per cocoon were not different between these Types. Type B also had the lowest mortality in 16-week experiments with changing temperatures.     

Population analysis in mass cultures of Tubifex tubifex

Mass cultures of Tubifex tubifex from Lake Orta were kept in the lab at 20 °C starting with different initial densities (10, 45, 86, 161 ind · jar^–1), with the aim of evaluating the effect of density on population numbers and on population parameters. The results show that density mainly controls fecundity, growth, maturation and ovigeration rates. Growth rates and mean number of eggs laid/ovigerous (R₀) are inversely related to density, but generation time appears to be directly related. Very low or very high initial densities display, at different times of the culture history, efficient density controls. Intermediate N₀ seem to bring about situations of bad control, easily leading to numerical overshoots. A possible implementation of a population dynamics model (Bonomi & Di Cola, 1980), originally used for laboratory observations on T. tubifex cohorts was considered, including some density control functions derived from our observations on cohort and mass cultures in some transfer rates and in fecundity rate.     

Mutualistic relationships between cohabiting tubificid species

Results from experiments with the three species constituting the dominant tubificid community of eutrophic lakes in Scandinavia, i.e. Tubifex tubifex, Limnodrilus hoffmeisteri and Potamothrix hammoniensis, suggested the involvement of mutualistic mechanisms. Previously Wavre & Brinkhurst, 1971; Brinkhurst, 1974 and McMurtry et al., 1983, described phenomena of this kind within a North American species complex involving T. tubifex and L. hoffmeisteri, as well.In mixed cultures, in comparison with monocultures of the respective species, I found that growth rate increased in the order of 50% and sexual maturity was reached earlier. Especially the three-species combinations rapidly increased in weight. Experiments with choice chambers, containing sediments enriched with the faecal pellets of each species alone or in species combinations, revealed specific reactions by the worms. As an average of three replicates, each starting with 45 recently hatched worms in equal proportions of the three species mentioned above, 14 chose the faeces of L. hoffmeisteri, 11 chose P. hammoniensis, 2 chose T. tubifex, 4 chose a combination of T. tubifex and L. hoffmeisteri and 4 chose blanks. Another 10 worms did not succeed in entering the choice chambers from the sandy substrate into which all worms were introduced and rapidly died off.The results seem to support the hypothesis that increased growth rate achieved in mixed cultures is due to each species selectively grazing concentrations of bacteria associated with the faeces of another species in the community. Earlier findings have shown that each species characteristically tends to cultivate only one species-specific bacterial strain at a time in its intestines (Wavre & Brinkhurst, 1971).Since the above species combination is by far the most frequently occurring oligochaete community in eutrophic lakes in Scandinavia and monocultures of any of the species involved are fairly uncommon under natural conditions, one may speculate that mixed cultures better utilize common available resources in accordance with experimental results.     

Some aquatic oligochaetes of the Nilgiris,South India

Eight species of aquatic oligochaetes, belonging to the families Naididae and Tubificidae, are reported, of which six species are new to the Nigiris. Tubifex tubifex known from Coonoor is reported again from this area.     

Relative influences of submersed macrophytes and bioturbating fauna on biogeochemical processes and microbial activities in freshwater sediments

1. Invertebrates and aquatic plants often play a key role in biogeochemical processes occurring at the water–sediment interface of aquatic ecosystems. However, few studies have investigated the respective influences of plants and bioturbating animals on ecological processes (nutrient fluxes, benthic oxygen uptake, microbial activities) occurring in freshwater sediments. 2. We developed a laboratory experiment in aquaria to quantify the effects of (i) one invertebrate acting as a bioturbator (Tubifex tubifex); (ii) one submersed plant with a high sediment‐oxygenating potential (Myriophyllum spicatum) and (iii) one submersed plant with a low sediment‐oxygenating potential (Elodea canadensis). 3. The tubificid worms significantly increased the fluxes of nitrogen at the water–sediment interface (influx of nitrate, efflux of ammonium), whereas the two plant species did not have significant influences on these nitrogen fluxes. The differences in nitrogen fluxes between tubificid worms and plants were probably due to the bioirrigation process caused by T. tubifex, which increased water exchanges at the water–sediment interface. Tubifex tubifex and M. spicatum produced comparable reductions of nutrient concentrations in pore water and comparable stimulations of benthic oxygen uptake and microbial communities (percentages of active eubacteria and hydrolytic activity) whereas E. canadensis had a very weak influence on these variables. These differences between the two plants were due to their contrasting abilities to increase oxygen in sediments by radial oxygen losses (release of oxygen from roots). 4. Our study suggests that the bioirrigation process and radial oxygen loss are major functional traits affecting biogeochemical functioning at the water–sediment interface of wetlands.     

Density-dependent processes in cohorts of Tubifex tubifex,with special emphasis on the control of fecundity

Laboratory cohort cultures of the tubificid Tubifex tubifex with different initial densities were carried out at 20° C with the condition of unlimited food. The main results were: 1) Intracocoon mortality was 37% of the laid eggs (observation of 689 eggs); 2) The principal bionomic parameters (generation time, r, R₀) appeared to be density dependent; 3) Recruitment was regulated through the percentage of worms that actually attained the ovigerous stage, specific fecundity, and the duration of the egg laying stage, which appeared to be inversely correlated with density.     

The occurrence of oligochaetes in lake chains receiving pulp mill waste and their relation to eutrophication on the trophic scale

Earlier conceptions of oligochaetes as indicators of trophy were somewhat enlarged to include more littoral, meiofaunal and naidid species. The amplitudes of different species on the oligotrophy-eutrophy axis seem to be generally large. Certain species which probably originally occur mainly in very humic environments seem also to be able to endure very strong organic loading caused by pulp mills. Species of this kind seem to be Dero digitata, Specaria josinae, Slavina appendiculata and Aulodrilus pluriseta. Chaetogaster langi and Arcteonais lomondi are also species which live in areas receiving pulp mill wastes. A. lomondi and D. digitata seem to be species living in greater depths than the naidids generally. Tubifex tubifex densities as high as 600000 ind · m^-2 were found near a pulp mill when the meiofauna method was used. A third of the T. tubifex were found deeper than 5 cm from the sediment surface. S. josinae and S. appendiculata may be found down to depths between 5 and 10 cm.