Influence of size and partner preference on the female function of the earthworm Eisenia andrei (Oligochaeta,Lumbricidae)

Many aspects of the reproduction and mating behaviour of earthworms remain poorly understood. In this study, we focused on body size as a possible trait that influences earthworm reproduction and mating processes. Eisenia andrei is a simultaneously hermaphroditic animal with reciprocal insemination and many hermaphrodites are expected to mate not primarily to get their own eggs fertilized, but rather to get the opportunity to fertilize the eggs of their partners. We investigated whether E. andrei has a size-dependent sex allocation, i.e. if larger earthworms are more biased toward female allocation and produce more egg mass and whether E. andrei has a size-related mate choice by studying the relationship between mating delay and cocoon production. To test this, we compared cocoon production between pairs of earthworms of equal and different size. Mature individuals of E. andrei were classified in two size classes (small and large) and we performed a two-factorial experiment with earthworm size and the size of the partner as factors. After copulation, earthworms were isolated and thereafter their mass and the number of cocoons they produced were recorded weekly for 18 weeks. We found no evidence of size-dependent sex allocation and we found no effect of size-assortative mating on cocoon production. With respect to the differences in the time to mate, the mating delay seems to indicate the existence of some kind of mate choice, independent of the earthworm size. Those earthworms that were matched sooner laid many cocoons, but those that waited a long time to mate laid fewer cocoons. This effect was stronger in those individuals paired with large partners, suggesting that some large partners are more desired ‘males’ than others; the reason for this remain as an open question. In general, our results confirm that earthworms are able to discriminate their partners and adjust their breeding effort accordingly.     

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.     

Sexual selection in earthworms: Mate choice,sperm competition,differential allocation and partner manipulation

Interpretations of hermaphroditism have been influenced by the long-held idea that organisms can be classified in a teleological series ranging from simple to complex, with humans placed at the top. Darwin considered that hermaphroditic animals, those which have both male and female sex organs, cannot be subject to sexual selection because the “union of sexes” makes them unable to perceive the attractiveness or rivalry of their partners, and moreover, because of their incapacity to exercise any kind of preference or choice. Until very recently, this view was generally accepted and justified on the grounds that the sensorial abilities of these animals are very limited and imperfect, basically because of their position at the lower level of the animal scale. In this paper we review new evidence that contradicts this vision. Indeed, recent studies suggest that earthworms are able to detect the degree of relatedness, the quality and mating status of their partners, and they are able to fine-tune control of transferred ejaculate volume and cocoon production. Overall, the picture that emerges is that earthworms are phenotypically very flexible, evaluation of partners is subject to intense selection, and sperm competition is important in shaping their mating behavior. Consequently, earthworms constitute an excellent model for studying sexual selection in simultaneous hermaphrodites. Interestingly, these results are more consistent with the latter observations of Darwin on earthworms than with his earlier conclusions on hermaphroditic animals. In his last book, written in 1881, Darwin affirmed, among other things, that despite being low in the scale of organization, earthworms possess some degree of intelligence. In the same book, Darwin postulated the role of earthworm behavior in soil formation, thus establishing the basis of modern soil ecology. Since earthworms exert considerable influence on the structure and function of terrestrial ecosystems, mating strategies that affect aggregations, dispersal or colonization may have important consequences on ecosystem functioning. Hence, earthworms are excellent models for integrating evolutionary and ecosystem ecology.     

Comparing four mitochondrial genes in earthworms – Implications for identification,phylogenetics, and discovery of cryptic species

Earthworms play a key role in soil ecology as they can reach high densities, are well known as soil engineers, and occupy a central position in soil food-webs. The identification of earthworms, however, is notoriously difficult and morphologically only possible for well-preserved adult specimens. Molecular markers could facilitate earthworm identification and would be a huge advantage in studies where it is important to species-specifically identify juveniles or where badly preserved specimens and remains of earthworms need to be identified. The aim of this study was to compare four mitochondrial genes (12S rRNA, 16S rRNA, COI, and COII) with respect to their value for identifying earthworms, calculating earthworm phylogenies, and discovering cryptic species. Our results indicate that all four genes are suitable for species identification. However, the genetic distances were approximately twice as high for the protein coding genes than for RNA coding ones. High genetic distances and deep genetic lineages, e.g. for Octolasion lacteum, Lumbricus rubellus and Aporrectodea rosea, indicate the possible presence of cryptic species and hamper molecular identification. The Bayesian analysis based on concatenated sequence data resulted in a phylogenetic tree with high posterior probabilities. The con-specific relationship of Aporrectodea spp. and Allolobophora spp. was not confirmed, underlining the ongoing discussion about the revision of these two genera. In conclusion, our findings suggest using 12S and 16S rRNA sequences as molecular markers for species identification whereas the COI gene is better suited to address genetic lineages and to explore possible cryptic species. Taxonomy and the identification of species are essential for most ecological studies. This study provides the needed molecular sequence information to develop molecular tools that can overcome many hurdles in studies on earthworms, their relationship and their ecology.     

The genetic consequences of hatchery-induced sperm competition in a salmonid

Supportive breeding is an important tool in conservation management, but its long-term genetic consequences are not well understood. Among the factors that could affect the genetics of the offspring is sperm competition as a consequence of mixed-milt fertilizations - which is still a common practice in many hatcheries. Here, we measured and combined the relevant factors to predict the genetic consequences of various kinds of hatchery-induced sperm competition. We drew a random sample of male Coregonus zugensis (an Alpine whitefish) from a hatchery program and quantified their in vitro sperm potency by integrating sperm velocity during the first minute after activation, and their in vitro milt potency by multiplying sperm potency with milt volume and sperm cell density. We found that not controlling for sperm density and/or milt volume would, at a constant population size, decrease the variance effective number of male breeders N_em by around 40-50%. This loss would decrease with increasing population growth rates. Partial multi-factorial breeding and the separate rearing of in total 799 batches of eggs revealed that neither sperm nor milt potency was significantly linked to egg survival. Sperm and milt potency was also not significantly correlated to other potential quality measures such as breeding tubercles or condition factor. However, sperm potency was correlated to male age and milt potency to male growth rate. Our findings suggest that hatchery-induced sperm competition not only increases the loss of genetic variation but may also induce artificial selection, depending on the fertilization protocol. By not equalizing milt volume in multi-male fertilization hatchery managers lose relatively more genetic variation and give fast-growing males a reproductive advantage, while equalizing milt volume reduces the loss of genetic variation and favors younger males who may have fast sperm to compensate for their subdominance at the spawning place.     

Inoculating maize fields with earthworms (Aporrectodea trapezoides) and an arbuscular mycorrhizal fungus (Rhizophagus intraradices) improves mycorrhizal community structure and increases plant nutrient uptake

Earthworms and arbuscular mycorrhizal fungi (AMF) are important macrofauna and microorganisms of the rhizosphere. The effect of the inoculation of soil with earthworms (Aporrectodea trapezoides) and mycorrhiza (Rhizophagus intraradices) on the community structure of mycorrhizal fungi and plant nutrient uptake was determined with split plots in a maize field. Maize plants were inoculated or not inoculated with AMF, each treated with or without earthworms. Wheat straw was added as a feed source for earthworms. Inoculating AMF significantly increased maize yield (p?<?0.05), and the yield was further enhanced by the addition of earthworms. Alkaline phosphomonoesterase activities, soil microbial biomass carbon (SMBC) and nitrogen (SMBN) increased with the addition of both earthworms and AMF. Soil inorganic N and available K were positively affected by earthworms, while available P showed a negative relationship with AMF. Treatment with both AMF and earthworms increased shoot and root biomass as well as their N and P uptake by affecting soil phosphomonoesterase and urease activities, SMBC, SMBN, and the content of available nutrients in soil. The applied fungal inoculants were successfully traced by polymerase chain reaction with novel primers (AML1 and AML2) which target the small subunit rRNA gene. The amplicons were classified by restriction fragment length polymorphism and sequencing. Moreover, field inoculation with inocula of non-native isolates of R. intraradices appeared to have stimulated root colonization and yield of maize. Adding earthworms might influence native AMF community, and the corresponding abundance increased after earthworms were inoculated, which has positive effects on maize growth.     

Earthworms and collembola relationships: effects of predatory centipedes and humus forms

Relationships between anecic earthworms (Lumbricus terrestris and Aporrectodea giardi) and the collembolan species Heteromurus nitidus (Templeton, 1835), which is known to be attracted to earthworms, were investigated in an 8-week laboratory experiment. Our aims were (1) to assess whether earthworms influence the population dynamics of H. nitidus, and (2) to study pathways of influence and how earthworm effects are modified by humus forms and predators. Using microcosms with three defaunated humus forms, then provided with earthworms and predators, we intended to demonstrate that, amongst possible favourable effects of earthworms on springtail populations, earthworm activity may provide greater access and more pathways for springtails to explore soil and avoid predation. We expected that the effects of predators (centipedes) on the abundance of H. nitidus would increase from less (calcic mull) to more (moder) compact soil, and we hypothesized that earthworms would reduce predation pressure on H. nitidus by providing escape routes through increased macroporosity. Humus forms and earthworms only affected the population size of H. nitidus under high predation pressure, when collembolan numbers were higher in calcic mull than in moder, and were increased by the presence of earthworms. These results corroborate the hypothesis that earthworms, by increasing soil macroporosity, improve the escape routes for Collembola and thus evade predation. In moder humus earthworms increased the density of H. nitidus whether predators were present or not, so we cannot exclude that earthworms were also directly beneficial to H. nitidus. However, the hypothesis of a functional relationship mediated by soil macroporosity seems relevant since it was supported by differences observed when considering body size. When two size classes were distinguished within populations of H. nitidus (1) the positive effect of earthworms in moder was observed only on larger Collembola (>1 mm), (2) the density of the larger Collembola was decreased by predation only in moder and not in mull, (3) the effects of predators on the smaller individuals were not influenced by the presence of earthworms whatever the humus form, and was not decreased by the presence of earthworms. Nevertheless, factors other than macroporosity may operate as the presence of earthworms in acidic mull led to an unexplained decrease in the abundance of small-sized H. nitidus.     

Competition between invasive earthworms (Amynthas corticis, Megascolecidae) and native North American millipedes (Pseudopolydesmus erasus, Polydesmidae): Effects on carbon cycling and soil structure

Invasive earthworms can have significant impacts on C dynamics through their feeding, burrowing, and casting activities, including the protection of C in microaggregates and alteration of soil respiration. European earthworm invasion is known to affect soil micro- and mesofauna, but little is known about impacts of invasive earthworms on other soil macrofauna. Asian earthworms (Amynthas spp.) are increasingly being reported in the southern Appalachian Mountains in southeastern North America. This region is home to a diverse assemblage of native millipedes, many of which share niches with earthworm species. This situation indicates potential for earthworm-millipede competition in areas subject to Amynthas invasion.In a laboratory microcosm experiment, we used two ¹³C enriched food sources (red oak, Quercus rubra, and eastern hemlock, Tsuga canadensis) to assess food preferences of millipedes (Pseudopolydesmus erasus), to determine the effects of millipedes and earthworms (Amynthas corticis) on soil structure, and to ascertain the nature and extent of the interactions between earthworms and millipedes. Millipedes consumed both litter species and preferred red oak litter over eastern hemlock litter. Mortality and growth of millipedes were not affected by earthworm presence during the course of the experiment, but millipedes assimilated much less litter-derived C when earthworms were present.Fauna and litter treatments had significant effects on soil respiration. Millipedes alone reduced CO₂ efflux from microcosms relative to no fauna controls, whereas earthworms alone and together with millipedes increased respiration, relative to the no fauna treatment. CO₂ derived from fresh litter was repressed by the presence of macrofauna. The presence of red oak litter increased CO₂ efflux considerably, compared to hemlock litter treatments.Millipedes, earthworms, and both together reduced particulate organic matter. Additionally, earthworms created significant shifts in soil aggregates from the 2000-250 and 250-53 μm fractions to the >2000 μm size class. Earthworm-induced soil aggregation was lessened in the 0-2 cm layer in the presence of millipedes. Earthworms translocated litter-derived C to soil throughout the microcosm.Our results suggest that invasion of ecosystems by A. corticis in the southern Appalachian Mountains is unlikely to be limited by litter species and these earthworms are likely to compete directly for food resources with native millipedes. Widespread invasion could cause a net loss of C due to increased respiration rates, but this may be offset by C protected in water-stable soil aggregates.     

Origin of the effect of earthworms on the availability of phosphorus in a phosphate rock

A series of trials was undertaken to evaluate the mechanisms by which earthworms increase the availability of phosphorus (P) in a phosphate rock (PR). In the 6 days that PR pellets were visible on the soil surface, there was no downward movement from the site of application in the presence of earthworms. Results from the glasshouse study with tillage treatments also suggest that earthworms play no direct role in the incorporation of the surface-applied PR. Addition of earthworms (Lumbricus rubellus (Hoff.)) to the soil incubating with SPR resulted in a 32% increase in Bray-extractable soil P after 70 days and increases ranging from 30 to 44% in bicarbonate-extractable soil P over the same period. Dissolution of PR, measured by extraction with 0.5 m NaOH, also increased in the presence of earthworms after 70 days from 24% (120 μg P) to 32% (160 μgP) of added P. These increases in dissolution of the PR in the incubating soil in the presence of earthworms appear to result largely from an increase in the degree of intimate contact of the PR particles with soil surfaces. This was confirmed by optical microscopy. Whereas estimates of ingestion rates, obtained by two traditional methods, indicated that L. rubellus ingested less than 5% of the incubating soil over 70 days, measurement of the proportion of soil affected by earthworms on an area basis using a frame technique ranged from 66% for Allolobophora caliginosa (Savigny) and 89% for L. rubellus, to 100% for the two species combined after 19 days. Results obtained with the frame technique explain more fully the effect of earthworms on the dissolution of the PR during incubation.     

Effects of epigeic earthworm (Eisenia fetida) and arbuscular mycorrhizal fungus (Glomus intraradices) on enzyme activities of a sterilized soil–sand mixture and nutrient uptake by maize

A pot experiment was conducted to investigate the effect of epigeic earthworm (Eisenia fetida) and arbuscular mycorrhizal (AM) fungi (Glomus intraradices) on soil enzyme activities and nutrient uptake by maize, which was grown on a mixture of sterilized soil and sand. Maize plants were grown in pots inoculated or not inoculated with AMF, treated or not treated with earthworms. Wheat straw was added as a feed source for earthworms. Mycorrhizal colonization of maize was markedly increased in AM fungi inoculated pots and further increased by addition of epigeic earthworms. AM fungi and epigeic earthworms increased maize shoot and root biomass, respectively. Soil acid phosphatase activity was increased by both earthworms and mycorrhiza, while urease and cellulase activities were only affected by earthworms. Inoculation with AM fungi significantly (p?<?0.001) increased the activity of soil acid phosphatase but decreased soil available phosphorus (P) and potassium (K) concentrations at harvest. Addition of earthworms alone significantly (p?<?0.05) increased soil ammonium-N content, but decreased soil available P and K contents. AM fungi increased maize shoot weight and root P content, while earthworms improved N, P, and K contents in shoots. AM fungi and earthworm interactively increased maize shoot and root biomass through their regulation of soil enzyme activities and on the content of available soil N, P, and K.     

Communities of microorganisms and invertebrates in soil-like bodies of soccer fields in Moscow oblast

Artificially created soil-like technogenic formations (STFs) of soccer fields are developed under combined action of intense technogenic and natural factors and processes, which cannot but affect the structure and biological activity of their microbial communities and mesofauna. The microflora of the STFs is very similar to the microflora of the background soddy-podzolic soils of Moscow oblast with respect to the composition of the physiological groups of microorganisms. However, they are drastically different in their quantitative characteristics. The numbers of all the trophic groups of microorganisms, except for the microscopic fungi, in the STFs are much higher than those in the zonal soils. An increased biological activity of the STFs is due to regular watering, heating, application of sand and mineral fertilizers, and technogenic turbation processes. The mesofauna of the STFs is represented by several ecological groups of earthworms, including soildwelling (endogeic) earthworms (Aporrectodea caliginosa), epigeic earthworms dwelling at the soil-litter interface (Lumbricus rubellus), and litter-dwelling earthworms (Eisenia foetida).     

Earthworms and rate of breakdown of soybean and maize residues in soil

A field survey was conducted to determine the numbers and biomass of earthworms in soils receiving different tillage and cropping treatments, and to investigate in a greenhouse study the effect of earthworms on the rate of breakdown of soybean (Glycine max) and maize (Zea mays L.) residues. The numbers and biomass of earthworms under continuous soybeans were greater than those present under maize, possibly due to the adverse effects of insecticide and anhydrous ammonia fertilizer used with maize. No-tillage doubled the population of earthworms under soybeans, when compared with ploughing. Numbers (141 m^?2) and biomass (26.5 g m^?2) of earthworms under no-till soybeans were still much lower than the numbers (1298 m^?2) and biomass (224.5 g m^?2) under pasture receiving heavy applications of animal manure. Using 16-1 pots in the greenhouse, the effect of 0, 15 (250m^?2) and 30 (500m^?2) earthworms (Lumbricus rubellus) pot^?1 on the rate of breakdown during 54 days of 50 g of soybean or maize residues in the Raub silt loam (Aquic Argiudoll) was studied. At 36 days, 60% of the soybean residues were recovered from pots to which no earthworms had been added, whereas in the presence of earthworms, only 34% of the soybean residues remained. In the absence of earthworms, 85% of the maize residues were recovered at 36 days, compared with only 52% in the presence of earthworms. At 36 days, 48% of the original maize residues added were still > 2 mm in length in the absence of earthworms, whereas only 26% were > 2 mm in length in the presence of earthworms. Earthworms also increased the aggregate stability of the Raub soil, when determined on moist (19–22% w/w) samples, but had no effect on soil water retention at ?33 and ?1500 kPa. The possible implications of greater earthworm activity on increasing residue incorporation and breakdown and subsequent effects on soil temperatures under no-till maize production are also discussed.     

Interactions between earthworms and their soil environment

Laboratory experiments were used to study the effect of food quantity and quality on the biomass of earthworms, and the influence of earthworms on plant growth and infiltration of water into soil. Earthworms with the most food gained weight faster than those with little or no supplementary food. The latter also failed to become reproductively mature. Earthworms lost weight on a nitrogenpoor diet, but this was not rectified by supplementing such food with inorganic nitrogen added to the soil 2 weeks before the worms. Ryegrass grown in soil in which earthworms (Allolobophora trapezoides) had been kept grew more slowly than in soil which had no previous worm activity, perhaps indicating that earthworms had converted relatively-available organic N into less available forms.Microscolex dubius gave the fastest infiltration rates of water into soil when clover mulch was present. With Eisenia foetida there was little effect of worm density on infiltration rates; the highest density significantly increased infiltration but only when clover hay had been mixed in the soil. The surface casting behaviour of the two earthworm species varied with the placing of the food offered.     

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.     

The earthworm (Aporrectodea caliginosa) primes the release of mobile and available micronutrients in soil

The objectives of our study were to quantify the impact of endogeic earthworms Aporrectodea caliginosa (Savigny) on iron (Fe), manganese (Mn) and zinc (Zn) mobility and availability in soil. Dried rye straw (Cecale cereale L.), clover aboveground parts (Trifolium pratense L.) or calcium carbonate were added to determine the effects on soil micronutrient mobility. To test the importance of soil–water saturation mediated by earthworms, soil samples were modified to 60% (control) and 100% (as in casts) water holding capacity (WHC). To assess availability of micronutrients, a cucumber plant (Cucumis sativus L.) bioassay were used. Earthworm casts had generally higher amounts of water-soluble micronutrients compared with bulk soils regardless of their moisture contents. The increased micronutrient mobility was more pronounced in casts from soil samples amended with plant residues (especially with straw) and was significantly higher than mobility in control soil for at least 1 week after the casts were deposited. Pre-incubation of soils amended with clover or straw with living earthworms for 4 weeks produced an increase in both shoot biomass and translocation rate of micronutrients (Mn, Zn) into xylem sap of cucumber compared to soils not worked by earthworms. The earthworm-mediated plant performances were determined 4 weeks after the earthworms were removed. The results demonstrated that earthworms can significantly impact the formation of mobile and available micronutrients in a soil. The relationship between micronutrient availability to cucumber plants and earthworm contribution to nitrogen (N) mineralization and micronutrient mobility are discussed.     

Effects of white-tailed deer on the native earthworm,Eisenoides carolinensis,in the southern Appalachian Mountains,USA

Research on earthworms in North America has focused on the effects of invasive earthworms, with few studies examining the ecology of native earthworm species. Deer have been shown to influence belowground processes through grazing, trampling, and fecal pellet deposition. We proposed that native earthworms in an oak-dominated forest in Virginia might benefit from increased organic matter provided by deer fecal material. We examined potential interactions between a common aboveground herbivore, the white-tailed deer (Odocoileus virginianus), and earthworms using laboratory and field experiments. In our laboratory experiment, we found that a native earthworm, Eisenoides carolinensis, and an invasive earthworm, Lumbricus terrestris both fared better in treatments with deer pellets compared with the treatment with leaf litter alone. In our field experiment, we used fences to exclude deer from six plots and left twelve plots unfenced to explore the effects of deer activity on earthworm biomass and density. We also examined the effects of deer on soil and vegetation characteristics. After three years, the amount of herbaceous cover was higher on fenced plots compared with unfenced plots. Although we found no other differences for vegetation and soil characteristics between fenced and unfenced plots, many of these variables were important as covariates in our models examining the effect of deer exclusion on earthworms, indicating plot-level (as opposed to treatment-level) variation in these variables. All identifiable earthworms were either E. carolinensis or Diplocardia spp. (both native species), with E. carolinensis making up 90% of the specimens. The total biomass of earthworms, as well as the biomass and density of adult and small juvenile earthworms, was greater on unfenced plots with deer activity compared with fenced plots. This study highlights the importance of above- and below-ground interactions in forest ecosystems by showing that E. carolinensis appears to benefit from the presence of deer and adds to our sparse knowledge of the ecology of this native earthworm.     

Flooding responses of three earthworm species,Allolobophora chlorotica,Aporrectodea caliginosa and Lumbricus rubellus,in a laboratory-controlled environment

To get a better understanding of earthworm’ responses towards flooding, three laboratory experiments were performed with the species Allolobophora chlorotica, Aporrectodea caliginosa and Lumbricus rubellus.Flooding response was determined in a pot experiment, in which the earthworms were incubated for 42 days in flooded or non-flooded soil, with or without heavy metal pollution. To determine moisture preference, earthworms were incubated for 9 days in aquaria with five compartments, containing soil with a moisture gradient (%, w/w), ranging from 35%, 45% (field capacity), 55%, 65% (saturated) to 65%+ (saturated and an extra water layer). Effects on earthworm health were studied by incubating earthworms of each species for 42 days in soil with the same range of moisture contents and determining the dry/wet weight ratio and dry weight gain as an indication of earthworm health.A. chlorotica was tolerant to water, although the worms tended to escape from flooded soil. Their health was significantly lower in the flooded soils (P<0.05). A. caliginosa showed little response to flooding. This species, however, was affected by the heavy metal pollution in the pot experiment. L. rubellus was sensitive towards flooding, with escape and avoidance behaviour being the main mechanism of survival. This species was able to survive when forced to stay in flooded soil for at least 42 days, but this significantly reduced its health (P<0.05).These results suggest that earthworms are able to survive in inundated soils, but there are large differences between species in response to flooding conditions.     

Impact of invasive earthworms on Ixodes scapularis and other litter-dwelling arthropods in hardwood forests,central New York state,USA

Invasive earthworms alter the structure of soils in northern hardwood forests, but the quantitative impacts on litter-dwelling invertebrates are unclear. Litter loss should reduce the habitat space, but nutrient-rich earthworm burrows might provide food resources. We investigated the impact of invasive earthworms on populations of Ixodes scapularis (black-legged ticks) and other litter-dwelling arthropods to determine the impact of a reduced litter environment. We used five pairs of one-hectare sites (earthworm invaded versus reference) within four separate contiguous forests in New York state. The presence of earthworms decreased the density of nymphal I. scapularis by 46.1% and larval I. scapularis by 29.3%. We also observed a dramatic decline in the total abundance of litter-dwelling arthropods with 69.9% of the arthropod population disappearing in the presence of earthworms. Additionally, litter arthropod populations declined disproportionately to leaf litter mass reduction indicating that the quality of the remaining litter material in the earthworm sites was poor. The impact of earthworm invasion on the litter environment and implications for the position of an important disease vector (I. scapularis) within the litter ecosystem are explored.     

Earthworms in New Zealand sheep- and dairy-grazed pastures with focus on anecic Aporrectodea longa

Earthworms play an important role as primary decomposers in the incorporation and initial mixing of plant litter. This study explored the response of earthworms to increasing fertiliser inputs, pasture production and livestock numbers (and their influence on food availability and soil physical condition) on six different managements in sheep-grazed and fifteen different managements in dairy-grazed pastures in a variety of New Zealand soils.Native earthworms were only found in some low-fertility pastures. Accidentally introduced peregrine earthworms, when present, dominate pasture soils. Of these, endogeic earthworms dominated the earthworm community and were positively associated with soil types with higher bulk densities. Peregrine anecic earthworms were absent from most hill-country sheep-grazed pastures, however in more fertile and productive dairy-grazed pastures they reached a biomass of up to 2370 kg ha^?1. Only anecic earthworms showed a positive response to the increasing pressures associated with higher potential dry matter inputs and liveweight loadings of grazing livestock on soil, while epigeic earthworms declined. The positive response of anecic earthworms probably reflects the combined effect of the increase in food resources, including dung and plant litter, available on the soil surface, and their lower susceptibility to livestock treading pressure. Anecic species may be a suitable substitute for incorporation of surface litter in those soils where livestock treading limits epigeic earthworm populations.This study confirmed previous observations of limited distribution of the introduced Aporrectodea longa in pastoral hill-country soils in the North Island, and their near absolute absence from the South Island of New Zealand. This would suggest that large areas of New Zealand pastoral farmed soils could benefit from the introduction of anecic species from other parts of New Zealand which already contain A. longa.     

Lumbricus terrestris counteract the effects of modified lignin biosynthesis on the decomposition of tobacco plant residues

The C and N transformations during decomposition over 26 d of root material from two lines of tobacco plants (Nicotiana tabacum L.) were compared in soil with or without earthworms (Lumbricus terrestris L.). The tobacco plants were either unmodified or genetically modified to reduce the activity of caffeic acid O-methyl transferase (COMT), which leads to plants with altered lignin structure and composition. In the absence of earthworms, C mineralization and net N immobilization were greater for the soil amended with reduced COMT roots than with the unmodified roots. In the presence of earthworms, C mineralization was still significantly greater for reduced COMT roots than for unmodified roots, but the difference was smaller, and the net N immobilization did not differ significantly between the two lines of plants.