Inbreeding and outbreeding reduces cocoon production in the earthworm Eisenia andrei

Earthworms are animals with reciprocal insemination. Eisenia andrei Bouché, 1972 is a simultaneous hermaphroditic earthworm that lives in manure heaps at high densities, with low opportunities of dispersal, thus very close inbreeding is expected. As the negative effects of inbreeding and outbreeding may be severe, we studied whether E. andrei adjusts its breeding effort according to the degree of mate relatedness. To test this, we performed laboratory experiments in which earthworms were mated with their sibs and with non-sibs from the same population and no-sibs from a geographically isolated population. Inbreeding and outbreeding matings caused a strong reduction of cocoon production, especially in genetic lines with high reproductive rates. As far as we know, this is the first study that indicates reproductive adjustment in earthworms according to the genetic divergence of their partners. Optimal outbreeding should be considered a crucial point in the management of breeding populations for applied purposes.     

The influence of livestock dung on the abundance of exotic and native earthworms in a grassland in south-eastern Australia

It is well known that organic matter in the form of dung is utilised as a food source by some earthworms, but little has been reported on the preferences of earthworms for different types of dung in agricultural settings. An experiment was carried out in spring in south-eastern Australia to evaluate the effect that dung from different livestock has on the abundance of earthworms in a grassland environment. We were particularly interested to compare the responses of native Australian earthworms (Megascolecidae) with those of exotic earthworms (Lumbricidae and Acanthodrilidae). The attractiveness of dung from sheep, cattle and horses was measured by determining the abundance and biomass of the resident earthworm species under each dung type at varying times after adding the dung to the soil surface (0, 10, 20 and 30 days). The earthworm population consisted of three exotic species, Apporrectodea trapezoides, Microscolex dubius and M. phosphoreus, and two native species, Spenceriella macleayi and S. bywongensis. Both the number of days that the dung was available to earthworms and the type of dung influenced the numbers and biomass of the earthworms found beneath the dung pats. Significant interactions existed between time and dung type when all adult earthworms were considered as one group and also when adults were split into individual species. The various species responded differently to the dung, but horse dung was generally the more preferred dung type. The significance of these results is discussed in terms of the management of dung in an Australian pastoral context.     

Influence of agricultural intensification on the earthworm community in arable farmland in the North China Plain

Two field experiments had been conducted in Huantai County, Shandong Province, east of China, with an effort to understand the impact of agricultural intensification on earthworm diversity and population density. Seven species of earthworms were identified in the two experiments. Average earthworm populations in the higher fertility soil (experiment B, 1.83% organic matter) were relatively abundant, with a population density of 105 indiv./m² and biomass of 57 g/m². Aporrectae trapezoids was the most dominant species. In the lower fertility soils (experiment A, 1.43% organic matter) the population density was only 51 indiv./m² and the average biomass was 30 g/m². Drawida gisti was the most dominant species. For both the experiments A and B, organic fertilizer (OF) and crop straw return increased earthworm abundance. The impact of chemical fertilizer (CF) on the earthworm population was found to depend on the amount of organic input. In experiment B, the earthworm biomass decreased when only winter wheat (Triticum aestivum) straw was input at three CF application levels. However, while both winter wheat straw (WS) and corn (Zea mays) stalk returned, there was no negative correlation between CF and earthworm density and biomass.     

C to N ratio strongly affects population structure of Eisenia fetida in vermicomposting systems

Food quality influences not only the size of earthworm populations but also their growth and reproduction rates. Here we studied the effect of C to N ratio of pig slurry in microbial biomass and activity and in the growth and reproduction of the earthworm Eisenia fetida. We set up a batch of twelve vermireactors, six each for low (11) and high C to N ratio (19) of pig slurry applied; three of each without earthworms (control) and three containing 500 mature earthworms (E. fetida). After 36 weeks C to N ratio significantly affected earthworm numbers (sevenfold greater in high C to N ratio) and population structure. Thus, in the low C to N ratio treatment the population was composed mainly by mature earthworms (60%), with a higher mean weight than in the high C to N treatment. However, in the high C to N ratio treatment, the population was composed mainly by juvenile and hatchling earthworms (70%). A rapid depletion of dissolved organic C (DOC) content was observed in all treatments. Although earthworms produced an increase in microbial biomass and activity in young modules, finally a decrease in older modules was recorded. The decrease in available carbon did not seem to affect the relationships established between earthworms and microflora.     

Depth of cocoon deposition by three earthworm species in mesocosms

Earthworms were maintained in two types of soil-filled mesocosm. Type 1, designed for use in soil-inoculation studies, was only 0.15 m deep. Sampling revealed the position at which cocoons were deposited by earthworms in mono-species culture. Whilst adequate for shallow-working worms, larger species may have experienced restricted burrow formation and associated cocoon deposition. Therefore, Type 2 mesocosms (1.0 m deep) were also used. Here, earthworms were found to burrow throughout the soil columns, but cocoons were mainly deposited within 0.25 m of the soil surface (95% overall). The deepest cocoon deposition was at 0.4 m by Lumbricus terrestris, although 45% of the cocoons for this species were located in the upper 0.05 m of the soil, compared with 70% and 71% for Aporrectodea longa and Octolasion cyaneum, respectively. Comparisons between mesocosms showed that their depth affected cocoon distribution in the soil and that differences were also present compared with field-collected results. Reasons for this are discussed, as are implications for soil inoculation with earthworms. If cocoons are viewed as a potential inoculum for soil restoration work, their harvesting and spreading in soil may assist successful colonisation.     

The efficiency of soil hand-sorting in assessing the abundance and biomass of earthworm communities. Its usefulness in population dynamics and cohort analysis studies

Pit digging and manually revising soil blocks is a frequently used method used for field studies of earthworm communities. The aim of this study was to compare the efficiency of hand-sorting (HS) to extract small earthworms, ca. 0.2 g, and the usefulness in studies of population dynamics and cohort analysis. Many earthworms are not recovered when revising manually the soil. Factors include soil characteristics, i.e. moisture, texture, etc. and also a human factor, which is more relevant if the study is conducted in the long-term. We used data collected in a field study of earthworm communities during 2 years in the savannas of Colombia. Small soil blocks (20 × 20 × 20 cm) were dug out in order to collect the smallest earthworms by washing-sieving (WS) and compare the results with the standard HS of large monoliths (100 × 100 × 50 cm). In fact, this methodology has rarely been addressed in earthworm population field studies. Our results showed that HS efficiency varied owing to the species and ranged from 31.4% up to 100% in the savanna and from 44% to 80% in the pasture, for two small species, i.e Aymara n. sp. (epigeic) and Ocnerodrilidae sp. (endogeic). In the case of the Glossodrilus n. sp. (endogeic) these values were similar, i.e. 51.7% and 58.1%, in the savanna and pasture, respectively. We also used frequency tables to calculate the average efficiency of HS 1 m² soil cores for each weight class in each species in order to obtain a population density correction factor. This allowed us to make corrections in earthworm density in the histograms for population dynamics analysis. We conclude that this method should be the modus operandi in long-term earthworm demography studies.     

Present knowledge on earthworm biodiversity in the State of Paraná, Brazil

In this paper we summarize the current knowledge on earthworm biodiversity in the State of Paraná, Brazil. Up to the present, 54 species of earthworms are known from the State, belonging to seven families and 19 genera. Native species (N = 34), dominated over exotics (N = 20). The most widespread exotics were Pontoscolex corethrurus (Glossoscolecidae) and several Amynthas spp. (Megascolecidae) and Dichogaster spp. (Acanthodrilidae), generally associated with anthropogenic sites. Of the native species, most (17 spp.) were in the genus Glossoscolex, frequently encountered in chronically wet soils. Further work is warranted, particularly more sampling efforts, but also ecological studies, given the potential biodiversity and agro-ecological importance of earthworms in Paraná.     

Life cycle and reproductive traits of the earthworm Aporrectodea trapezoides (Dugès, 1828) in laboratory cultures

The parthenogenetic earthworm Aporrectodea trapezoides (Dugès, 1828) is widely distributed all over the world due to European agricultural practices. In order to provide baseline life cycle data, cocoons were obtained from field-collected individuals and their features and viability, incubation period, number of hatchlings and mortality rate were recorded. Singleton and twin earthworms from this first experiment were cultured from hatching during a 490-day period under controlled conditions with biomass, survival, reproductive condition and cocoon production recorded at intervals of 15 days. On average, individuals of isolated-reared A. trapezoides reached maturity at day 153 and body weight at maturity was approximately 1 g. In order to record reproductive traits and differences between field-collected and laboratory-reared individuals, 40 microcosms with an isolated earthworm (20 with field-collected individuals and 20 with laboratory-reared ones) and 40 containing groups of three (20 with each type of individual) were maintained during a complete year under controlled conditions. The amount of soil per individual was the same in both types of microcosm. Both the individuals kept in isolation and those cultured in groups produced cocoons, hence completely proving the obligatory parthenogenetic reproduction in this species without copulation or need of any physical-chemical stimulus. In general, isolated earthworms produced a significantly higher number of cocoons than those in groups of three, and the same was recorded for laboratory-reared earthworms when compared with field-collected ones. This study highlights the importance of knowing the life cycle and reproductive traits of one possible key species in soil management due to its vast distribution and high density in soils, and the species’ highly recommended use in applied studies because of its ease of culture.     

Selective feeding of the earthworm Hormogaster elisae (Oligochaeta,Hormogastridae) in laboratory culture

Selective feeding of the earthworm Hormogaster elisae was investigated by granulometric analysis, chemical fractionation and physical fractionation of the soil in which representatives were cultivated, and of their casts. H. elisae behaved as an endogeic species, mainly consuming soil from which it weakly but positively selected the organic fractions of greatest size (mainly free organic matter) and negatively selected the largest mineral fraction (coarse sand). No significant selection of intermediate size fractions was recorded. The 0–2 μm granulometric fraction (clays) was also selected; the results suggest that some of the organic components of this size fraction can also be used by the species.     

Using process-based modelling to analyse earthworm life cycles

To understand the life cycle of an organism, it is important to understand the physiological processes that govern growth and reproduction. In this paper, we re-analyse a life-cycle data set for the earthworm Eisenia veneta, using a process-based model. The data set comprises measurements of body size and cocoon production over 200 days, at two temperatures (15-25 °C) and two densities (five and 10 worms per container, but with the same worm:soil weight ratio). The model consists of a set of simple equations, derived from Dynamic Energy Budget (DEB) theory. The dynamics of growth and reproduction are simultaneously described by the model, using very few parameters (five parameters for four curves). This supports the use of this model for efficient analysis of earthworm life-cycle data, and to interpret the effects of stressors. However, there was considerable inter-individual variation in the response, hampering the interpretation of the temperature and density effects. A temperature increase corresponded to an increase in the rate constants for growth and reproduction (with the same factor), without affecting the other parameters, as expected from DEB theory. Changing the earthworm density hardly affected the growth curves, but had an unexpected effect on reproduction: at higher densities, the worms start to produce cocoons at a larger body size and the maximum reproduction rate was lower. This study confirms the use of DEB as a reference model for earthworms, and using this model, we can recognise that temperature has a predictable effect on the life cycle of E. veneta. Furthermore, this analysis reveals that the effects of density are less clear and may involve a change in energy allocation that requires further study.     

Can the invasive earthworm,Amynthas agrestis,be controlled with prescribed fire?

Biological invasions are one of the most significant global-scale problems caused by human activities. Earthworms function as ecosystem engineers in soil ecosystems because their feeding and burrowing activities fundamentally change the physical and biological characteristics of the soils they inhabit. As a result of this “engineering,” earthworm invasions can have significant effects on soil physical, chemical and biological properties. The species Amynthas agrestis (family Megascolecidae) was introduced to the United States from Asia, and has expanded its distribution range to include relatively undisturbed forests. Here, to clarify life history traits, we reared individuals under seven different conditions of food provision using litter, fragmented litter and soil, and also analyzed the stable isotope ratios of field-collected specimens to investigate their food resources in the field. Second, we examined whether prescribed fire can be used to manage invasive earthworms. We constructed eight experimental plots, each with 100 individuals of A. agrestis each, and burned half of the plots. The feeding experiment showed that the earthworms in units containing soil and some form of organic matter (litter and/or fragmented litter) produced many cocoons, indicating that litter and fragmented litter are important food resources for them. Stable isotope analyses also supported this result. During the experimental fires, average soil temperature at 5 cm depth increased by only 7.7 °C (average maximum of 32.2 °C). Litter mass was significantly reduced by the fires. Although numbers of A. agrestis and cocoons recovered from burned and unburned plots were not different, the viability of cocoons was significantly lower in burned plots. Fire may also reduce the survival rate of juveniles in the next year by depriving them of their preferred food resource. Most native earthworms in the United States live in the soil, while many invasive ones live in the litter layer and soil surface. Therefore, prescribed fire could be a viable tool for control of invasive earthworms without negatively impacting native earthworm populations.     

Mate choice of an endogeic earthworm revealed by microsatellite markers

Endogeic earthworms are difficult study subjects due to the cryptic medium in which they live; thus, only the behaviour of epigeic and anecic earthworms has been studied before. We used microsatellite markers as a tool to elucidate the mate choice processes of Hormogaster elisae, an endogeic earthworm. It was shown to normally mate with two partners, preferably of the same size that are found in close proximity thereby eliminating the need for long-distance dispersion, which could explain the previously observed high genetic differentiation between populations. The genetic analyses of the sperm within each of its four spermathecae showed a uniform distribution with no signs of differential storage of sperm from different partners.     

Impact of earthworms on decomposition of garden refuse

Summary Decomposition of garden refuse was studied in containers with and without the earthworm species Eisenia andrei and Lumbricus rubellus. The reduction of cellulose and hemicellulose was greater where earthworms were present. Respiration was similar regardless of the presence of earthworms, whereas dry matter reduction, on average, was greatest without earthworms. The earthworm biomass decreased during the 58 days of the experiment; E. andrei increased in biomass, whereas L. rubellus died out.     

Genetic variation in desiccation tolerance of Dendrobaena octaedra cocoons originating from different climatic regions

The aim of this study was to examine genetic variation in desiccation tolerance in cocoons of the parthenogenetically reproducing earthworm Dendrobaena octaedra by comparing populations originating from different geographic regions (Denmark, Norway and Finland), representing large differences in precipitation and temperature. In one experiment, the tolerance of the three populations to increasing desiccation stress in the range from 100 to 91.6% relative humidity (RH) was examined, aiming to represent ecologically relevant RH values. In a second experiment, the effect of cocoon size on desiccation tolerance was investigated at 92.3% RH in the same three populations. There were highly significant differences in desiccation tolerance between populations, indicating a high genetic differentiation of this trait in D. octaedra. Cocoons from Denmark were much more sensitive (71±14% mortality at 91.6% RH) than cocoons from Norway (21±4% mortality) and Finland (4±5% mortality). Cocoons of worms from Finland and Norway were significantly larger than cocoons produced by worms from Denmark suggesting that cocoons from Denmark lost water at a higher rate when subjected to low humidity. Assuming that slow dehydration is necessary for physiologically based protection mechanisms it may be expected that desiccation tolerance is positively correlated with cocoon size. However, within each of the populations cocoon fresh weight did not have any significant impact on desiccation tolerance. When all populations were pooled there was a significant positive effect of cocoon fresh weight on desiccation tolerance, explaining about 20% of the total variation (linear regression). It seems therefore that genetic variation of desiccation tolerance in D. octaedra cocoons is related to variation in both cocoon size and other, physiologically based tolerance mechanisms.     

Maize residue application reduces negative effects of soil salinity on the growth and reproduction of the earthworm Aporrectodea trapezoides,in a soil mesocosm experiment

We studied the effects of maize residue application on some life-cycle parameters of the earthworm Aporrectodea trapezoides in saline agricultural soils with electrical conductivity (EC) ranging from 1.58 to 7.35 dS m⁻¹. This experiment was carried out under controlled laboratory conditions for 150 days. Results showed that soil salinity significantly affected the growth and reproduction of earthworms, decreasing survival, numbers and mean fresh weights of adults, juveniles and cocoons. Maize residue application gave a greater survival of earthworms at all salinity levels, but the differences were only significant at an EC of 7.35 dS m⁻¹, although the mean weight of adult earthworms was significantly increased by maize residue application at all salinity levels. At an EC of 1.58 dS m⁻¹ and 3.35 dS m⁻¹, the application of maize residues gave significantly higher numbers of cocoons and juveniles, but in soils with 5.26 dS m⁻¹ and 7.35 dS m⁻¹ earthworms did not produce any cocoons over the experimental period, irrespective of maize residue application. These results indicated that maize residue application alleviated the negative effects of soil salinity on the growth and reproduction of A. trapezoides up to 3.35 dS m⁻¹, above which maize residues only increased the growth but not on the reproduction of earthworms.     

Terbuthylazine and carbofuran effects on growth and reproduction within three generations of Eisenia andrei (Oligochaeta)

Sublethal effects of terbuthylazine and carbofuran on the growth and reproduction of Eisenia andrei were investigated over a period of three generations. Reproduction was assessed by measuring the coccon production of worms treated chronically with pesticides. Inhibition of cocoon production was found in the parental generation. Hatchlings were raised from cocoons to provide the F₁ generation. During raising a more rapid growth of juveniles treated with terbuthylazine was observed, compared with the growth of untreated worms. The increase in vitality was also found in cocoon production. Groups treated with terbuthylazine produced more cocoons than controls. The F₂ generation was raised from hatchlings of the F₁ generation, and here, also the terbuthylazine treatments increased earthworm growth, but not cocoon production. Exposure to carbofuran decreased cocoon production in all generations. Growth of the F₁ generation was not influenced by low concentrations of carbofuran.     

Abundance of biogenic structures of earthworms and termites in a mango orchard

A comparative study of the spatial distributions and the quantity of biogenic structures produced by earthworms and termites (Odontotermes nilensis and Ancistrotermes guineensis) has been conducted in a mango orchard at Thiès (Senegal).This study showed that surface biogenic structures may represent a large amount of modified soil (up to 536.5 g m⁻²) which vary depending upon the seasons and the species. Whilst the quantity of casts was independent on the season (178.6 g m⁻²), O. nilensis sheetings fluctuated with the seasons. In addition, we show that the spatial organisation of surface biogenic structures fluctuates with seasons. It displays patches ranging from 5 to 15 m. There is a link between the distribution of earthworm casts and the vegetation. In addition, spatial distribution was also linked to the biology of constructing species. We observed that the A. guineensis’ filling structures were mainly located under the mango trees during the dry season where the stems and the brushwoods were abundant. It appears that the spatio-temporal distribution of the biogenic structures under study depended upon two main factors: season and vegetation. However, depending upon the biology of the engineer, these two factors influenced the spatial distribution of structures in different ways.     

Is Hormogaster elisae (Oligochaeta,Hormogastridae) a predator of mites and springtails?

The aim of this work was to determine whether the endogeic earthworm Hormogaster elisae [1] is involved in the active or passive predation of microarthropods at El Molar (Madrid, Spain). Different techniques were employed to study the gut content, and the casts of H. elisae earthworms cultivated in the laboratory. The casts consisted mainly of mineral particles and plant remains as well as a few microarthropods, nematodes and their remains. The gut contents were similar in composition, although no microarthropod remains were found, except for a single springtail (order Poduromorpha) in one earthworm's gizzard. The results suggest that H. elisae may accidentally ingest microarthropods along with soil. The microarthropods found in the casts may have colonized them after their deposition since none were found in isolated casts.     

A viable technique for tagging earthworms using visible implant elastomer

Earthworms perform many ecosystem services. However, due to their body shape, mucus covering, and subterranean behaviour, it has been very difficult to successfully tag individual animals for experimental purposes. This paper examines the potential use of commercially available visible implant elastomer (VIE) tags to mark earthworms. Two laboratory experiments were conducted employing four temperate earthworm species by injection of the VIE and making regular assessments. Results showed that the biologically compatible polymer tags, injected into earthworm muscle, remained in the animal and could be visually located after a period of 12 months. Tagging did not affect growth to maturity, mating or cocoon production of Lumbricus terrestris. VIE tagging can now be viewed as a viable technique for marking this and other earthworm species.     

Biochemical responses of the earthworm Eisenia fetida andrei exposed to contaminated artificial soil,effects of carbaryl

The aim of this study was to investigate the effects of carbaryl, at different concentrations and exposure times, on the biochemical responses of the earthworm, Eisenia fetida andrei (E. andrei) to: (1) elucidate the mechanisms of action of carbamate compounds; and (2) explore the potential for using these responses as biomarkers to monitor carbamate-contaminated soils or for use in sublethal assays to test chemicals in the laboratory. Thus, earthworms were exposed to increasing concentrations of carbaryl (CA) (12, 25 and 50 mg kg⁻¹ artificial soil) for different periods of time (2, 7 and 14 days) using the standard soil test method. The activities of the following enzymes were measured: catalase (CAT), acetylcholinesterase (AChE), glutathione reductase (GR), glutathione-S-transferase (GST), methoxyresorufin-O-deethylase (MROD) and NADH (NADH Red) and NADPH (NADPH Red) cytochrome reductases activities. Levels of lipid peroxides (LP), peroxidizable lipids (LPI), total glutathione (total GSH) and the percentage of oxidized glutathione (%GSSG) were also determined. Our results showed that cholinesterases are the main target of carbaryl in E. andrei. Carbaryl also inhibited biotransformation enzyme activities but did not induce oxidative stress. Changes were detected in phase I and acetylcholinesterase activities upon exposure to the lowest dose of carbaryl (12 mg kg⁻¹). This demonstrated the sensitivity of these parameters in E. andrei. In addition, discrimination between doses and exposure times was clearer when all the responses were considered rather than a selective choice of biomarkers. This confirms our previous finding that a suite of biochemical responses could be used as a sublethal assay for testing chemicals in the laboratory or for soil contamination surveys.