Density, biomass and vertical distribution ofAporrectodea caliginosa (Savigny 1826) (Oligochaeta, Lumbricidae) in Benghazi, Libya

Studies were conducted during the period May 1993 to April 1994 on the density, biomass and vertical distribution ofAporrectodea caliginosa, a common species of earthworm found in the Benena farms in Benghazi, Libya. The soil of the farm was a clay loam, pH 7.3, and the organic matter averaged 4.2%. Maximum density and biomass ofA. caliginosa were recorded from October to December 1993 and again during March and April 1994, and minimum values were recorded from May to July 1993. A juvenile dominant population was observed during the summer. This was followed by an increase in subadults and adults during the autumn, winter and spring seasons. A positive correlation of the moisture and an inverse correlation of soil temperature on the density and biomass of these animals were discernible. A. caliginosa mainly confined their activities to the surface organic zone (0–10 cm depth) of the soil for most of the months studied.     

Internal regulation of reproduction seasonality in earthworm Dendrobaena octaedra (Savigny, 1826) (Lumbricidae, Oligochaeta)

The study was conducted on Dendrobaena octaedra—a small epigeic earthworm species common in different forest types. In the laboratory the P (parent animals collected in forest) and F1 generations were cultured separately in containers filled with 50 g artificial soil. The containers were kept at 15±0.5 °C, 80% humidity and constant artificial light of low intensity. Every month during the 47 months of culture, the animals and cocoons were removed from the soil by washing on a sieve, weighed, and replaced into new soil. Individuals of the F1 generation did not reproduce continuously. Cocoon production was seasonal, despite culture in constant conditions throughout the whole experiment. Reproduction was highest in spring and summer, and dropped in the winter months. Seasonality characterized the fraction of animals reproducing as well as the number of cocoons produced. The observed seasonal changes in the cocoon production of the F1 generation cultured in constant conditions suggest that internal regulation of reproduction may exist in the earthworm D. octaedra. External factors like temperature, moisture, photoperiod or food supply, which could be responsible for seasonality of reproduction were missing.     

Schwermetallbelastung von Aporrectodea caliginosa (Oligochaeta,Lumbricidae) im Raum Kiel

Heavy metal content in Aporrectodea caliginosa (Oligochaeta, Lumbricidae) in the city of Kiel (Germany, Schleswig-Holstein) In November 1995 the content of lead, cadmium, copper and zinc in earthworms of the Aporrectodea caliginosa species was investigated at 28 sites of the Kiel area, as well as at one reference site (Belauer See, ca. 20 kilometres south of Kiel), and compared with the heavy metal content in the soil taken from all those sites. As for the lead and copper content, a positive correlation could be established between the earthworms and the soil. However, the lead content in the earthworms did not depend only on its amount in the soil, but also on soil pH and calcium content. Their copper content decreased exponentially as weight increased. The content of lead, cadmium and copper in A. caliginosa suggested an influence of urban soil pollution on the heavy metal content in earthworms. According to the grouping of heavy metal content in the earthworms, which was done in the course of the research work, the city of Kiel ranges among a minor to a medium degree of pollution caused by the investigated heavy metals.     

Competitive interactions affect the growth of Aporrectodea caliginosa and Lumbricus terrestris (Oligochaeta: Lumbricidae) in single- and mixed-species laboratory cultures

Negative interactions between earthworms may arise from high earthworm population densities. Under high populations in the field, niche separation or migration away from competitive pressure may help to regulate a multi-species population to a given level. This may not be possible in laboratory experiments, leading to an increase in competitive interactions which may alter earthworm growth rates and affect decomposition and nutrient mineralization processes. The objective of this experiment was to determine how growth rates of the endogeic earthworm Aporrectodea caliginosa Sav. and the anecic earthworm Lumbricus terrestris L. are affected by increasing population density and container size in both single- and multi-species cultures. Earthworm growth responses were compared in 1-L cylindrical pots containing disturbed soil and in 2.3-L PVC cores containing undisturbed soil. The relationship describing intra- and inter-specific competition was not affected by container type for both species. Nonetheless, decreasing the container size restricted the growth of L. terrestris in both single- and multi-species cultures, but only restricted the growth of A. caliginosa in multi-species cultures. For both species, a population density greater than one individual per litre reduced earthworm growth rates significantly, while weight loss in monocultures occurred when there were more than 10 A. caliginosa, and more than three L. terrestris per litre. Growth rates of both species were restricted in all population density treatments including the lowest of 0.9 individuals per litre. Further work is needed to find the population density at which growth rates are not affected and which may be used as an appropriate population in laboratory pot experiments to measure the effects of earthworms on soil processes and plant growth.     

Isolation of polymorphic microsatellite markers in Aporrectodea icterica (Savigny 1826)

Earthworms play a major role in soil dynamics acting as modifiers of properties and soil characteristics. Although population genetics is a promising approach to get a better understanding of their ecology, the use of molecular tools in earthworm studies is still scarce. Here, we developed and analyzed seven microsatellite loci for Aporrectodea icterica, a common endogeic species of most temperate natural and agricultural soils, with the aim to investigate its dispersal capacity in further researches. Although sequences of a fragment of the mitochondrial gene cytochrome oxidase subunit I (COI) showed the existence of two mitochondrial lineages within the species, with a mean divergence between them of 10%, microsatellite data proved that these two COI lineages are interbreeding and form part of a single species.     

Relationships between casts of geophagous earthworms (Lumbricidae,Oligochaeta) and matric potential

A laboratory study was conducted to determine the effects of matric potentials between -25.4 and-2.0 kPa on the mechanical dispersion of fresh and aged casts produced by Aporrectodea caliginosa, A. rosea, and A. trapezoides. We also examined the effects on dispersion of the matric potential at which the air-dried casts were rewetted. Dispersion from subsurface casts up to 6 days old and uningested aggregates was influenced, but dispersion from fresh casts was not influenced, by the matric potential of the soil core from which the samples were collected. Dispersion from subsurface casts and uningested aggregates increased as the matric potential of the soil core increased from -25.4 to -2.0 kPa. Cast dispersion was not influenced by the earthworm species which produced the cast. Little or no clay was mechanically dispersed after the casts had been air-dried and rewetted, and the matric potential at which casts were rewetted had little influence on dispersion.     

Life cycle traits of the parthenogenetic earthworm Octolasion cyaneum (Savigny, 1826)

This laboratory-based study provides baseline life cycle data for the obligatory parthenogenetic earthworm Octolasion cyaneum. Singleton and twin hatchlings were cultured individually with biomass, survival and reproductive condition recorded at 4-weekly intervals during a complete year. After maturation, cocoon production, masses and incubation time were also recorded along with viability and number of hatchlings per cocoon. Individual mean mass of singletons was significantly (P < 0.05) greater than twins at the outset (0.042 and 0.025 g respectively) and remained so until week 52 (2.22 and 1.96 g respectively). Singletons matured more rapidly than twins (24 vs. 32 weeks respectively) and produced more cocoons than twins (3.2 and 2.2 coc worm⁻¹ (4 weeks)⁻¹ respectively). Approximately 20% of all viable cocoons produced twins. Singleton hatchlings weighed significantly (P < 0.05) more than twin hatchlings (0.032 and 0.018 g respectively) but there was no significant difference (P > 0.05) between mean masses of singleton (mean masses 0.033 and 0.032 g) or twin (0.017 and 0.018 g) hatchlings produced by singleton and twin parents. The likelihood that a cocoon contained twins or a singleton was not influenced by the singleton/twin status of the parent. There was no significant difference (P > 0.05) in the incubation times of cocoons produced by singletons and twins (129 and 128 days respectively).     

Glyphosate Sublethal Effects on the Population Dynamics of the Earthworm Eisenia fetida (Savigny, 1826)

Pesticides’ sublethal effects are not regularly taken into account when assessing agrochemical’s toxicity. With the objective of detecting chronic, sublethal effects of the widely used herbicide glyphosate, an experiment was performed using the earthworm Eisenia fetida as model organism. Earthworm adults were randomly assigned to three glyphosate treatments: control (no glyphosate), regular dose for perennial weeds, and double dose. Six E. fetida individuals were placed in each pot. Two random pots were taken weekly from each treatment and the number of adults, individual weight, number of cocoons, and presence and number of young earthworms were recorded. A matrix analysis was performed with the data. The matrix population model built showed that while the control population had a positive growth rate, both glyphosate treatments showed negative growth rates. The results suggest that under these sublethal effects, non-target populations are at risk of local extinction, underscoring the importance of this type of studies in agrochemical environmental risk assessment.     

In vivo 31P and 1H HR-MAS NMR spectroscopy analysis of the unstarved Aporrectodea caliginosa (Lumbricidae)

This study demonstrates that ³¹P and ¹H high resolution-magic angle spinning (HR-MAS) nuclear magnetic resonance (NMR), a recently developed NMR technique, can be applied to the in vivo analysis of metabolites from an unstarved earthworm. The endogeic earthworm Aporrectodea caliginosa was cut into lengths and then the different body parts (anterior, middle, posterior) with the gut content were analyzed. With the HR-MAS NMR, metabolites show well-resolved signals, whereas, with conventional NMR, spectra are highly dependent on the gut content. ³¹P HR-MAS NMR has been used to evaluate the effect of an acute exposure of the earthworm to glyphosate. Our observations support a low toxicity of the herbicide and suggest that glyphosate could be trapped in the cutaneous mucus. Earthworms could therefore play a role in horizontal dispersion and stabilization of glyphosate in the drilosphere. Phosphorylated metabolites, such as phospholombricine and lombricine, were clearly identified and their amount measured during experiments. The ¹H HR-MAS NMR method offers the opportunity to measure, on the same sample and simultaneously, both the hydrosoluble metabolites and lipids. The data on lipid location and relative succinate concentration shed light on the physiological and metabolic functions of the different body parts of the earthworm.     

Leaf litter acceptance and cast deposition by peregrine and endemic European lumbricids (Oligochaeta: Lumbricidae)

In Central Europe a rich endemic earthworm fauna exists. The ecology of most of these species has not been studied. In laboratory mesocosms we examined leaf litter acceptance and cast deposition of a total of 30 species, 21 of which were endemic. In both experiments earthworms, especially small species, exhibited a variety of behaviors. Hornbeam litter was consumed at higher C/N values by anecic species, but some epigeics still did not accept it. Surface cast deposition varied between 0 and 100% among small endogeics. Most anecic species deposited their casts belowground, but the model anecic species, Lumbricus terrestris was an exception: 79% of its total cast was deposited on the surface. Epigeics and endogeics did not clearly separate in these behavioral traits. Refinement of ecological categorization of Lumbricidae needs to include data on lesser known species.     

Changes in respiration rate and some physicochemical properties of soil during gut transit through Allolobophora molleri (Lumbricidae,Oligochaeta)

Summary Some physicochemical and biological measurements were carried out on the gut content and casts of Allolobophora molleri, an earthworm which lives in humid soils of Northern Spain. In the anterior part of the gut, water (22% of moist weight of soil) and soluble organic matter (27.4%) had been added to the ingested soil and pH had increased from 5.75 to 7.0. The amount of water-soluble compounds decreased sharply in the middle and posterior parts of the gut and were hardly detectable in control soil or casts. The average O₂ consumption, measured at 28° and 21°C, indicated respectively 2.75-to 12-fold increases in microbial respiration in the gut content compared to the non-ingested soil. These results extend the hypothesis of a mutualistic digestion in earthworms previously proposed for tropical endogeic species.     

Leaf-litter consumption and assimilation by juveniles of Lumbricus terrestris L. (Oligochaeta,Lumbricidae) under different environmental conditions

Summary The rate of consumption of dandelion leaves per g earthworm dry weight per week was described by non-linear functions of soil temperature, soil water potential, and food availability. The optimum temperature and soil water potential for food consumption are about 22°C and-7 kPa, respectively. Zero consumption occurred at about-40 kPa. Food consumption increased with greater food availability, but only up to 1.05 (dandelion) and 1.23 (grass) g dry weight per g earthworm dry weight per week at 15°C. A general consumption function to account for all three environmental factors is given. The assimilation rate per g earthworm dry weight per week was defined as the sum of the growth rate and the maintenance rate. Maintenance was calculated according to respiratory measurements reported previously, whereas growth was measured. High temperatures and limiting environmental conditions, such as a low food availability and a low soil water potential, led to an increase in the assimilation efficiency of Lumbricus terrestris. At-7 kPa and 15°C, L. terrestris assimilated 55 and 43% of the ingested dandelion if 0.25 and 1.0 g dry weight of food was available per g earthworm dry weight per week, respectively. it is concluded that L. terrestris has a strong, direct effect on the decomposition of highly palatable plant materials.     

Effects of Aporrectodea caliginosa (Savigny) on nitrogen mobilization and decomposition of elevated‐CO2 Charlock mustard litter

This study was conducted to improve our understanding of how earthworms and microorganisms interact in the decomposition of litter of low quality (high C : N ratio) grown under elevated atmospheric [CO₂]. A microcosm approach was used to investigate the influence of endogeic earthworm (Aporrectodea caliginosa Savigny) activity on the decomposition of senescent Charlock mustard (Sinapis arvensis L.) litter produced under ambient and elevated [CO₂]. Earthworms and microorganisms were exposed to litter which had changed in quality (C : N ratio) while growing under elevated [CO₂]. After 50 d of incubation in microcosms, C mineralization (CO₂ production) in the treatment with elevated‐[CO₂] litter was significantly lower in comparison to the ambient‐[CO₂] litter treatment. The input of Charlock mustard litter into the soil generally induced N immobilization and reduced N₂O‐emission rates from soil. Earthworm activity enhanced CO₂ production, but there was no relationship to litter quality. Although earthworm biomass was not affected by the lower quality of the elevated‐[CO₂] litter, soil microbial biomass (C_mic, N_mic) was significantly decreased. Earthworms reduced C_mic and fungal biomass, the latter only in treatments without litter. Our study clearly showed that A. caliginosa used the litter grown under different [CO₂] independent of its quality and that their effect on the litter‐decomposition process was also independent of litter quality. Soil microorganisms were shown to negatively react to small changes in Charlock mustard litter quality; therefore we expect that microbially mediated C and N cycling may change under future atmospheric [CO₂].     

Growth and survival of Eisenia fetida (Sav.) (Oligochaeta: Lumbricidae) in relation to temperature,moisture and presence of Enchytraeus albidus (Henle) (Enchytraeidae)

Summary The aim of this study was to investigate the environmental requirements of Eisenia fetida (Lumbricidae) and its relation to Enchytraeus albidus (Enchytraeidae). Specimens of Eisenia fetida were cultured at two different temperatures (15°C and 25°C) and moisture conditions (50% and 80%) in presence or absence of Enchytraeus albidus. Eisenia fetida grew best at the higher temperature and amount of moisture. Enchytraeus albidus impaired the growth of Eisenia fetida at the higher temperature. When Enchytraeus albidus was present, the mortality of Eisenia fetida increased.Interaction between Eisenia fetida and Enchytraeus albidus was shown, although the mechanisms remain unclear. These species, coexisting in the same habitat (compost), appear to have slightly different niches: Eisenia fetida favours warmer, moister conditions than Enchytraeus albidus.Dedicated to the late Prof.Dr. M.S. Ghilarov     

Clone distribution of the earthworm Eiseniella tetraedra (Sav.) (Oligochaeta: Lumbricidae) across an altitudinal gradient on subarctic mountains of NW Europe

In earlier studies, we have shown that clone diversity of the parthenogenetic earthworm Eiseniella tetraedra increases from the upper reaches of rivers in northern Sweden towards their mouths. Now we survey brooks in the Scandes Mountains in the watershed between Sweden and Norway where major rivers originate. Using starch gel enzyme electrophoresis, we found 37 clones in a total catch of 379 individuals from six mountains. The most abundant clone made up 48.3% of the individuals collected. It was present on most mountains and was found at different elevations. In comparison with other clones it may represent a general-purpose genotype adapted to environmental conditions ranging from alpine through to subalpine to boreal habitats in the mountains. Diversity of clone assemblages decreased with increasing elevation. On four mountains, one to two clones were found at higher elevations. Passive downstream dispersal of E. tetraedra propagules from wider areas of the mountains was responsible for the more diverse clone pools in the lower reaches of the brooks (i.e., “small rivers behave like large ones”). Two clone groups, which deviated from the norm clone in their number of enzyme variants, were evenly distributed among different elevations. Therefore, we could not correlate genotype differences (i.e., adaptation of clones to mountain elevations). Clone pool similarities among the mountains were low on average (range 0–58%) but in a cluster of four mountains, similarities varied from 46% to 58%. Clone pool similarities between different elevations of the same mountain ranged from 27% to 83%. One mountain brook was sampled over 3 years to assess clone turnover. Only the norm clone was found in upstream habitats but it and three other clones were recorded downstream in at least 2 years. Ten clones were found once in the latter habitat as well.     

Phospholipid fatty acid profiles and xylanase activity in particle size fractions of forest soil and casts of Lumbricus terrestris L. (Oligochaeta,Lumbricidae)

Earthworms are key agents in organic matter decomposition, as they remove surface plant litter material and mix it with mineral soil. Plant litter material is comminuted in the gizzard of anecic earthworms and this is enhanced if sand particles are available. We hypothesize that this comminution of soil and litter will result in changes in the distribution of soil organic matter and soil microorganisms in the different particle-size fractions. We investigated soil organic matter content, xylanase- and microbial activity and community structure in bulk soil and particle size fractions of Lumbricus terrestris L. casts and in soil with and without the addition of beech litter.Earthworm gut passage did not affect the particle-size distribution but the content of soil organic matter was decreased in the fine sand fraction in treatments without litter (−6.80%) and increased in treatments with litter (+33.23%). The soil organic matter content of the clay fraction tended to be higher in earthworm casts. Xylanase activity was at a maximum in the fine sand fraction, lower in the coarse sand fraction and at a similar minimum in the silt- and clay-sized fraction. In the coarse sand fraction of the cast and litter treatments xylanase activity was increased by 39.1% and 124.8%, respectively. In the silt-sized fraction of casts the addition of litter increased xylanase activity (+58.6%) whereas, in casts without litter it was decreased (−36.25%). In the particle size fractions of casts, the content of bacterial PLFAs was decreased in the fine sand fraction and tended to be decreased in the clay fraction compared to the respective fractions in soil. In the silt fraction the fungal-to-bacterial PLFA ratio was higher in casts than in soil.We conclude that earthworms stabilize soil organic matter in cast aggregates predominantly by increasing the soil organic matter content in the clay fraction where it becomes protected against microbial attack. Organic matter in the coarse and fine sand fractions is decomposed primarily by fungi; xylanase is very active in these sand fractions and incorporation of litter into these fractions by the earthworms increased fungal biomass. Comminution of litter during passage through the earthworm gut increased the biomass and activity of fungi also in the silt fraction. The use of PLFA profiles in combination with other quantitative microbial methods improves the understanding of stabilizing and mobilizing processes in earthworm casts.     

Identification of uncultured bacteria tightly associated with the intestine of the earthworm Lumbricus rubellus (Lumbricidae; Oligochaeta)

The bacteria associated with the intestine and casts of the earthworm Lumbricus rubellus Hoffmeister, 1843, were examined by direct counts, culturability studies, 16S rRNA gene clone libraries, and fluorescent in situ hybridization (FISH). A significant fraction, 24-47%, of the total numbers of prokaryotes remaining in the intestine after casting were tightly associated with the intestinal wall. Bacterial 16S rRNA gene clone libraries constructed from washed earthworm intestinal tissue suggested that the bacterial community was dominated by a few phylotypes that were either absent from, or in low abundance, in the casts. The specific phylotypes present depended on the date of sampling and included representatives of the Acidobacteria, Firmicutes, β-Proteobacteria, and one phylogenetically deep, unclassified group. Juvenile earthworms subsequently collected contained three of the four phylotypes observed in the intestine clone libraries. The Firmicutes phylotype was examined by FISH and was found to be a short rod that represented only a small fraction of the total population of the juvenile samples. These results suggested that the microbial community tightly associated with the intestine was dominated by a small number of phylotypes and that this association was opportunistic rather than obligate.