Cocoon viability and evidence for delayed hatching by the earthworm Lumbricus terrestris in a laboratory-based study.

Clitellate Lumbricus terrestris, obtained from 5 commercial suppliers (A-E) and also field collected (F) - grassland in Preston, Lancashire, UK, were kept under controlled environmental conditions (15 °C and 24 h darkness) in a sterilised loam soil and surface-fed with horse manure. Survival, biomass and cocoon production was monitored every 4 weeks over 1 y. Collected cocoons were maintained in water-filled Petri dishes on filter paper. Time to hatch and cocoon viability was recorded over a 2 y period. Cocoon production ranged from 15.1 – 32.2 ind.-1 y-1. Cocoon production was initially low followed by a period of high production (12-36 weeks) and then fell (36-52 weeks). Time for cocoon hatching ranged from 132-731 days. Hatching success after 2 years was 58–90% across treatments, with a total viability (including cocoons dissected after the 2 year period) of 88-94%. Evidence of 2 distinct hatching peaks was recorded, separated by a period of approximately 12 months in treatments of most of the commercially obtained earthworms. Cocoon incubation periods are in excess of those previously recorded under similar laboratory conditions (e.g. 90–280 days). Furthermore, viability is also higher than previously recorded (e.g. 67.9–83%). These differences are mainly attributable to the extended length of cocoon observation. Origin, age, unknown pre-treatment (in A-E) and experimental conditions (e.g. a constant temperature regime) may have influenced incubation times. However, it is suggested that asynchronous and delayed hatching within cohorts and ability for cocoons to remain viable for extended periods allows this K-selected species to maximise reproductive potential. This proposed “bet-hedging” strategy is worthy of further laboratory and field-based investigation

Interactions with earthworm communities: a laboratory-based approach with potential applications for soil restoration

The role of earthworms in improving soil fertility and structure is widely recognised. As a result earthworms (often single species populations) have been deliberately introduced into pasture and arable land by man in attempts to improve plant production and into degraded land in order to bring about soil amelioration. The potentioal of earthworms employed in land restoration programmes may be enhanced by inoculating sites with a combination of species from different ecological groupings which have different roles in soil processes. In order to acheive the type of success envisaged by such projects, detailed information on the ecology and interactions between candidate species is required. This research investigated inter- and intra-specific interactions in terms of growth, maturation, cocoon production and survival, between five earthworm species (Allolobophora chlorotica (Savigny), Aporrectodea caliginosa (Savigny), Aporrectodea longa (Ude), Lumbricus rubellus (Hoffmeister) and Lumbricus Terrestris (Linnaeus)) under laboratory conditions. Cultures were initially maintained under optimal environmental conditions. Selected environmental variables (e.g food poison, food particle size and soil bulk density) were manipulated in order to quantify observed species interactions and subject earthworms to condditions that could be encountered at restored sites. Results demonstrated that all species could be successfully cultured under laboratory conditions. Techniques developed during the work may have applications in commercial large-scale rearing of earthworms in addition to production of species cohorts for toxicological testing and further laboratory experimentation. All experimental species were found to co-exist under the specified laboratory conditions, however both positive and negative inter- and intra-specific interactions were recorded throughout the study. The intensity of negative (competitive) interactions was attributed to the degree of niche overlap between earthworms and was dependant upon the species present, their stage of development and ability to adapt th limiting environmental conditions. Some deep burrowing earthworm species were found to increase the production of smaller conspecifics and other smaller earthworm species. it is suggested that this type of positive (commensal) association arose from smaller individuals feeding on concentrated and easily digestible organic matter present in the castings of larger earthworms. In addition to the potential applications of culture techniques described earlier, this research has contributed to the knowledge of an important ecological group, provided data for competition theory and should also prove valuable because of its implications for soil restoration

An oasis of fertility on a barren island: Earthworms at Papadil, Isle of Rum

The Isle of Rum, Inner Hebrides, has an impoverished earthworm fauna as the soils are generally acidic and nutrient-poor. Species associated with human habitation are found around deserted crofting settlements subjected to “clearances” in the mid-19th century and at Kinloch, where a large volume of fertile soil was imported from the mainland around 1900. Earthworms, and the dew worm Lumbricus terrestris L. in particular, were investigated at Papadil, an abandoned settlement and one of the few locations on Rum where a naturally developed brown earth soil is present. The small (1.5 ha), fertile location is isolated, so was also suitable for field experimentation. Visits over six years allowed dew worm distribution to be assessed within low lying grassland and woodland and also within an adjacent sloping broadleaved woodland. The factors limiting dew worm distribution at the site were investigated with associated translocation to adjacent uninhabited areas. Small scale spatial dynamics were studied with density manipulation and containment experiments where Visual Implant Elastomer marking of individuals was utilised. Translocations from streamside woodland to adjacent grassland was successful over a short period (5 months), but the colonies did not persist over a longer term (5-6 years). Field trials with earthworm tagging were successful, but highest tag recovery rate was 25%. Where adults/sub-adults were removed, recruitment of juveniles was notable. Exceptionally large (>12 g live mass) individuals were found in soils of terraces on wooded slopes, suggesting that dew worms may be long lived at this location, where food is abundant and relatively few terrestrial predators are present

Earthworms of an urban cemetery in Preston: General survey and burrowing of Lumbricus terrestris.

Cemeteries in the UK are predominantly represented by grassland areas which have a variety of origins. Each can act as a haven for wildlife and numerous studies have looked at the flora and fauna present and in particular lichens associated with gravestones which offer chronological assessment. However, very few studies have looked at invertebrates in such settings and surprisingly, few if any have investigated earthworms - given the folklore associating these animals with the decomposition of human remains in the soil. This investigation set out to identify which species of earthworm were present in an urban cemetery in Preston and to discover how deep the animals were burrowing and indeed, if they were capable of burrowing to a depth of 2 metres – the depth at which bodies are usually buried. Nine species of earthworm were found, representing all three ecological categories, epigeic, endogeic and anecic. Burrow configurations were measured through casting with polyurethane resin. Vertical burrows of clitellate Lumbricus terrestris penetrated to a mean depth of 0.49 m (maximum 0.59 m), a function of soil type and water table. Where previous land use had created a relatively impervious layer below the soil surface, complex branched burrows of L. terrestris were found. These were significantly (p<0.001) shorter (mean depth 0.21 m) but confirmed the behavioural flexibility that this species of earthworm is known to exhibit. The presence of a healthy earthworm community in the grassland of the cemetery may well assist ecosystem services, but assistance with decomposition of human remains is unlikely

Interactions of juvenile Lumbricus terrestris with adults and their burrow systems in a two-dimensional microcosm

O objetivo deste trabalho foi avaliar as interações de juvenis de Lumbricus terrestris com indivíduos adultos e com sistemas de galerias herdados. O experimento foi realizado usando microcosmos bidimensionais de Evans como unidades experimentais. Adultos de L. terrestris foram colocados em 16 unidades experimentais (um indivíduo por unidade) e mantidos no escuro a 17ºC juntamente com oito unidades experimentais inabitadas, por dois meses. Os adultos foram removidos de oito unidades selecionadas aleatoriamente e juvenis foram adicionados a todas as unidades experimentais (um indivíduo por unidade), em três tratamentos, com oito repetições: 1, com um adulto em um sistema de galerias herdado (ABJ); 2, sozinho em um sistema de galerias herdado (BJ); e 3, sozinho em uma unidade experimental inabitada (J). A proporção de juvenis observados ocupando as galerias feitas pelos adultos foi significativamente diferente nos tratamentos ABJ (48%) e BJ (75%). A biomassa média dos juvenis ao final do experimento diferiu significativamente entre os tratamentos e foi maior no tratamento J (4.04±0.39 g) em comparação com os tratamentos BJ (3.09±0.93 g) e ABJ (2.13±0.64 g). Os resultados sugerem uma influência negativa tanto da presença de um adulto quanto do seu sistema de galerias no crescimento dos juvenis. A competição intraespecífica explica parcialmente este fenômeno, porém novas investigações devem ser feitas para examinar como um ambiente herdado (galerias) pode afetar negativamente o crescimento de juvenis.The objective of this work was to evaluate interactions of Lumbricus terrestris juveniles with adults and with inherited burrow systems. An experiment was set up using a two dimensional Evans' boxes microcosm. Adult L. terrestris were added to 16 boxes (one individual per box) and kept in darkness at 17°C along with eight unoccupied boxes for two months. The adult L. terrestris were removed from eight randomly selected boxes, and L. terrestris juveniles were added (one juvenile per box), composing three treatments with eight replicates: 1, with an adult in an inherited burrow (ABJ); 2, alone in an inherited burrow (BJ); and 3, alone in a previously uninhabited box (J). The proportion of juveniles occupying adult burrows observed was significantly different in treatments ABJ (48%) and BJ (75%). The mean mass of juveniles at experimental termination differed significantly among treatments and was greater in treatment J (4.04±0.39 g) in comparison to the BJ (3.09±0.93 g) and ABJ treatments (2.13±0.64 g). Results suggest a negative influence of both the presence of an adult and its burrow system on juvenile growth. Intraspecific competition partially explained this, but further investigation is required to examine how an inherited environment (i.e. burrow) could negatively affect the growth of juveniles

Assessment of avoidance behaviour by earthworms (Lumbricus rubellus and Octolasion cyaneum) in laboratory-based linear pollution gradients.

Avoidance behaviour by earthworms is recognised as a valuable endpoint in soil quality assessment and has resulted in the development of a standardised test (ISO 17512-1: 2008) providing epigeic earthworms with a choice between test and control soils. This study sought to develop and evaluate an avoidance test utilising soil-dwelling earthworms in linear pollution gradients with Visible Implant Elastomer (VIE) tags used to identify individual organisms. Sequential experiments were established in laboratory-based mesocosms (0.6 m x 0.13 m x 0.1 m) that determined the relative sensitivities (in terms of associated avoidance behaviour) of Octolasion cyaneum and Lumbricus rubellus at varying levels of polluted soil and also assessed the influence of introduction point on recorded movement within gradients. In an initial gradient (0, 25, 50, 75, 100% polluted soil), both species exhibited a clear avoidance response with all surviving earthworms retrieved (after 7 days) from the unpolluted soil. In a less polluted gradient (0, 6.25, 12.5, 18.75, 25%) L. rubellus were retrieved throughout the gradient while O. cyaneum were located within the 0 and 6.25% divisions, suggesting a species-specific response to polluted soil. Results also showed that the use of a linear pollution gradient system has the potential to assess earthworm avoidance behaviour and could provide a more ecologically relevant alternative to the ISO 17512: 2008 avoidance test. However, further work is required to establish the effectiveness of this procedure, specifically in initial chemical screening and assessment of single contaminant bioavailability, where uptake of pollutants by earthworms could be measured and directly related to the point of introduction and retrieval

Effects of silver nanoparticles on survival, biomass change and avoidance behaviour of the endogeic earthworm Allolobophora chlorotica

Increasing commercial application of silver nanoparticles (Ag NP) and subsequent presence in wastewater and sewage sludge has raised concerns regarding their effects in the aquatic and terrestrial environment. Several studies have employed standardised acute and chronic earthworm-based tests to establish the toxicological effects of Ag NP within soil. These studies have relied heavily on the use of epigiec earthworm species which may have limited ecological relevance in mineral soil. This study assessed the influence of Ag NP (uncoated 80 nm powder) and AgNO3 on survival, change in biomass and avoidance behaviour in a soil dwelling (endogiec) species, Allolobophora chlorotica. Earthworms were exposed for 14 days to soils spiked with Ag NP or AgNO3 at 0, 12.5, 25, 50 and 100 mg kg-1 either separately for survival and biomass measurement, or combined within a linear gradient to assess avoidance. Avoidance behaviour was shown to provide the most sensitive endpoint with an observable effect at an Ag NP / AgNO3 concentration of 12.5 mg kg-1 compared with 50 mg kg-1 for biomass change and 100 mg kg-1 for survival. Greater mortality was observed in AgNO3 (66.7%) compared with Ag NP-spiked soils (12.5%) at 100 mg kg-1, attributed to increased presence of silver ions. Although comparison of results with studies employing Eisenia fetida and Eisenia andrei suggest that the A. chlorotica response to Ag NP is more sensitive, further research employing both epigeic and endogeic earthworms under similar experimental conditions is required to confirm this observation

Aporrectodea caliginosa, a relevant earthworm species for a posteriori pesticide risk assessment: current knowledge and recommendations for culture and experimental design

Ecotoxicological tests with earthworms are widely used and are mandatory for the risk assessment of pesticides prior to registration and commercial use. The current model species for standardized tests is Eisenia fetida or Eisenia andrei. However, these species are absent from agricultural soils and often less sensitive to pesticides than other earthworm species found in mineral soils. To move towards a better assessment of pesticide effects on non-target organisms, there is a need to performaposterioritestsusingrelevantspecies.TheendogeicspeciesAporrectodeacaliginosa(Savigny,1826)isrepresentative of cultivated fields in temperate regions and is suggested as a relevant model test species. After providing information on its taxonomy, biology, and ecology, we reviewed current knowledge concerning its sensitivity towards pesticides. Moreover, we highlighted research gaps and promising perspectives. Finally, advice and recommendations are given for the establishment of laboratory cultures and experiments using this soil-dwelling earthworm species

Is tagging with visual implant elastomer a reliable technique for marking earthworms?

Visual implant elastomer (VIE) has recently been employed to investigate different aspects of earthworm ecology. However, a number of fundamental questions relating to the detection and positioning of the tag, its persistence and potential effects on earthworms remain unknown. Seven earthworm species belonging to three ecological groupings, with different pigmentation and burrowing behaviour, were tagged using different coloured VIE. External inspection after two days, one week and 1, 10 and 27 months were followed by preservation, dissection and internal inspection. Tags could be seen in living specimens to 27 months, and dissection revealed that in most cases they were lodged in the coelomic cavity, held in place by septa. However, over longer time periods (more than two years), the chlorogogenous tissue tended to bind to the tags and made external observation increasingly difficult. Migration of the VIE material towards the posterior of the earthworm and potential loss of the tag were only observed on rare occasions, and a recovery rate in excess of 98% was recorded. By introducing a reasonable amount of VIE into segments, just after the clitellum, this technique can become a valuable tool in earthworm ecology and life history studies, particularly in short-medium term laboratory and field experiments