Observations on the life history of Limnodrilus hoffmeisteri (Annelida,Tubificidae) from the Little Calumet River in temperate North America

The reproductive period for L. hoffmeisteri as observed in the Little Calumet River (41°34′22″N. 87°28′30Prime;W) occurs from early fall through late spring. The period is marked by the development of the reproductive organs in the early fall months, followed by the development of sperm products within the sperm sac. The female organs appear to mature in middle to late winter with the appearance of nutritive granules followed by the developing eggs in early spring. This cycle is completed in early to late spring with the appearance of cocoons containing developing embryos. It is also apparent that a low level of reproductive activity occurs throughout the rest of the year. This is usually observed in worms with developed sperm sacs and sperm products, having matured penis and some developed egg sacs with nutritive granules. Eggs have not been observed during this low level of reproductive activity.     

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.     

Method for distinguishingLimnodrilus hoffmeisteri andLimnodrilus claparedeianus (Oligochaeta,Tubificidae) and its applicability in Lake Suwa

It is still next to impossible to distinguish species using immature worms of theLimnodrilus genus. A method was developed to separate mixed immature populations ofLimnodrilus hoffmeisteri andLimnodrilus claparedeianus into each species. The ratio of setal upper tooth length to lower tooth length, inL. hoffmeisteri andL. claparedeianus, ranged from 0.9 to 1.6 and from 1.3 to 2.1, respectively. Even if the median value of the frequency overlapped, this indistinguishable portion did not exceed 6% of each population.     

羽摇蚊幼虫和霍甫水丝蚓的生态毒理学研究

本文以羽摇蚊幼虫和霍甫水丝蚓为对象,进行了丁基磺毒杀作用的试验。结果表明,丁基磺不仅污染环境,而且对这两种水生生物均有较高的毒杀作用;这两种水生生物对其毒性都分别产生不同的症状;在低浓度下,亦产生不同效应;不同浓度丁基磺对摇蚊幼虫24小时毒理试验LC₅₀为256.2ppm,对水丝蚓LC₅₀为25.8ppm;不同季节出现的毒性效应均有差异。在试验结果的基础上,对水丝蚓中毒后出现了不同类型的症状;温度、酸碱度等不同生态因素对丁基磺毒性的影响以及加强水丝蚓生态毒理学工作的必要性等问题进行了讨论。     

Toxicity of Santander Bay Sediments to the Euryhaline Freshwater Oligochaete Limnodrilus hoffmeisteri

The freshwater euryhaline oligochaete Limnodrilus hoffmeisteri was selected for use in bioassays with polluted sediment from Santander Bay. It is easy to culture; is tolerant of low to moderate, up to 15‰, salinity; and is common in oligohaline conditions in European and North American estuaries. Worms were collected from an estuarine population and kept in unpolluted sediment for between 2 and 4 weeks, under laboratory conditions, at 7–8.5‰ salinity and 22.5 °C. Sediment from different sites in Santander Bay were sieved through 250 μm mesh and adjusted to a salinity of approx. 7‰ prior to the bioassays, either by adding sea water or dechlorinated tap water to the overlying water. High levels of ammonia in some sediment, which may confound results in ecotoxicity bioassays, were reduced by oxidation of the sediments in shallow trays. Sediment bioassays were performed with sexually mature Limnodrilus hoffmeisteri worms in 250-ml beakers, with a 1:3 ratio of sediment:water and 4 worms per baker. Endpoints in the 14-day bioassay were % mortality, adult final biomass, % adults that have shown resorption of the clitellum, number of cocoons, and burrowing behaviour. It was possible to rank the sites according to their toxicity using both mortality rates and sublethal effects. The control site had the following values for the endpoints: 5% mortality, ( ) 2.40 ± 1.52 cocoons per beaker and 1.271 ± 0.470 mg dw adult final biomass. The most toxic sediment resulted in 65% mortality, resorption of the clitellum in 67% of the adults, no production of cocoons and a low final biomass ( =0.681 ± 0.489 mg dw per adult). A second site had high mortality (60%) and no reproduction, although resorption of the clitellum did not occur in surviving animals. The remaining sites showed similar mortality (35–42%), and at only one of them was low reproduction observed (0.8 ± 0.447 cocoons per beaker). Behavioural effects, measured as length of galleries in a fixed area of the test-vessel at the end of the bioassay, were significant compared with control at only one site. Multivariate analysis showed the mortality gradient to be the strongest, with a second unassociated gradient representing clitellum resorption. The mortality gradient was associated with Cu and Zn concentration, and PAH and Pb possibly with resorption.