Seasonal variations in growth and reproduction of the earthworm Perionyx excavatus (Oligochaeta: Megascolecidae)

 One-week-old juveniles of Perionyx excavatus were cultured in urine-free cow manure for 16 weeks in three different seasons to find out the influence of environmental factors on growth and reproduction. The biomass of worms increased gradually until the 16th week in all seasons. There was no significant (F=2.51) variation in biomass between the three seasons; however, the growth rate varied significantly (F=50.49, P<0.01). During the pre-clitellar period, the growth rate (mg/g) increased steeply (1013.17±41.33 in the monsoon season, 728.64±15.5 in winter and 463.16±22.96 in summer) until the worms attained maturity (5–8 weeks) and from then onwards gradually decreased after the commencement of cocoon production. Worms attained maturity when the mean weight of each worm ranged from 167.46 mg to 197.13 mg. The cumulative number of cocoons varied significantly (F=26.07, P<0.01) with season. Similarly, the rate of cocoon production also varied significantly (F=62.06, P<0.01). The average rate of cocoon production was 7.23, 0.99 and 0.53/worm/week in the monsoon season, winter and summer, respectively. By week 16, the ratio of weight gain to the initial weight of 1-week-old juveniles was 1 : 43.13 in the monsoon season, 1 : 30.49 in the winter and 1 : 23.69 in the summer. The maximum mass gain, growth rate, and cocoon production and earliest attainment of maturity were recorded during the monsoon season, and were attributed to the lowest range of fluctuating temperatures and high humidity compared with during winter and summer. The growth rate of worms in all seasons was inversely proportional to the number of cocoons produced. Further, the higher the rate of cocoon production, the lower the weight of individual cocoons. Received: 1 July 1997     

Growth and cocoon production by the earthworm Metaphire houletti (Oligochaeta) in different food sources

 Quantitative observations on the biology of Metaphire houletti were made in cow and horse manure and oak litter in laboratory conditions over a period of 240 days. The study revealed that copulation is not a prerequisite for production of viable cocoons, indicating that M. houletti may be parthenogenetic. The mean growth rate was 2.86 mg worm^–1 day^–1 reaching sexual maturity at 45 days and producing 0.015 cocoons worm^–1 day^–1 (kept singly) and 2.82 mg worm^–1 day^–1, reaching sexual maturity at 45 days and producing 0.03 cocoons worm^–1 day^–1 (kept in batches) in cow manure; 4.08 mg worm^–1 day^–1, reaching sexual maturity at 46 days and producing 0.02 cocoons worm^–1 day^–1 (kept singly) and 2.97 mg worm^–1 day^–1, reaching sexual maturity at 45 days and producing 0.016 cocoons worm^–1 day^–1 (kept in batches) in horse manure; 3.73 mg worm^–1 day^–1 reaching sexual maturity at 45 day and producing 0.023 cocoons worm^–1 day^–1 (kept singly) and 2.73 mg worm^–1 day^–1, reaching sexual maturity at 47 days and producing 0.028 cocoons worm^–1 day^–1 (kept in batches) in oak litter. After an incubation period of 31.9±1.2 days 82% of the cocoons hatched with a mean of 1.12±0.06 hatchlings per cocoon. The earthworms reared in batches did not demonstrate any advantage over those reared singly in all substrates. Higher growth rates were observed in earthworms raised singly than those raised in batches in all substrates. Received: 30 April 1998     

Parthenogenesis, polyploidy and reproductive seasonality in the Taiwanese mountain earthworm Amynthas catenus (Oligochaeta, Megascolecidae)

Amynthas catenusTsai et al., 2001 is a terrestrial earthworm belonging to the Pheretima complex of the family Megascolecidae. It is endemic to Mt. Hohuan of central Taiwan at elevations of 2985-3004 m. Its reproductive organs showed various stages of degeneration in the present study. The spermathecae varied from being absent (athecal) to three pairs in VI-VIII (sexthecal), and the prostate glands from a large, symmetrical pair to complete absence. For the 44 specimens examined from May 2008 to May 2010, there were 47.7% athecals, 36.4% sexthecals and 15.9% intermediates. Results of a flow cytometric analysis showed that there were three DNA ploidy levels - diploid, triploid and tetraploid (2n, 3n, and 4n) - for the athecals but only diploid for the sexthecals. The intermediates consisted of diploids and triploids. The diploids had 2n = 112 and the triploids 3n = 168. The haploid chromosome number of A. catenus was 56. Spermatogenesis occurred throughout the year with the highest activity in summer for both athecals and sexthecals, but the number of mature ova peaked in summer for the athecals and in spring for the sexthecals. There was no significant difference in mean number of mature ova produced between the athecals and the sexthecals, but the sexthecals had significantly higher spermatogenetic activity than the athecals. For all specimens examined, sperm were present in testes and seminal vesicles but not in spermathecae, an indication of parthenogenesis in the species.     

Reproduction of the African earthworm,Eudrilus eugeniae (Oligochaeta) — cocoons

Summary Although various authors have contributed to our knowledge of the biology of Eudrilus eugeniae some basic facts about the life cycle and reproduction are still not fully documented. Quantitative observations were made of the cocoons at 25 °C in different substrates. The incubation period for 166 cocoons was 16.89 days, based on cocoons produced by worms between the ages of 70 and 100 days. These cocoons produced a mean 2.12 hatchlings per cocoon after incubation in cattle manure, moist filter paper and distilled water. A smaller batch of cocoons incubated in cattle manure produced a mean of 2.7 hatchlings per cocoon. The hatching success of the cocoons was 84% in cattle manure, 50% in distilled water, and 48% on moist filter paper. The reproductive capabilities of E. eugeniae and Eisenia fetida were compared.     

A defined medium for the study of growth and reproduction of the earthworm Eisenia fetida (Oligochaeta)

Summary The feeding requirements of earthworms have not been fully established. A vermiculite matrix was used to determine the dietary effects of various organic substances. Vitamins, DNA, and humic acid as additives improved growth and allowed reproduction of Eisenia fetida in a cellulose-based medium. Mature worms were not able to adapt to the medium and 20-day-old worms were used. Rates of growth and cocoon production were slightly less in a defined medium (7% organic content) than in a cow-manure control medium (70% organic content). The medium is likely to prove useful as a reference medium for obtaining biological information.     

Effects of ivermectin in dung pats on earthworm (Megascolecidae) populations and pat degradation in Japanese grassland

The effects of residual ivermectin in dung pats on earthworm activity and dung decomposition in Japanese grassland, where Megascolecidae are the dominant group of dung decomposers, were studied. Artificial cowpats containing 0, 0.1, and 1 mg ivermectin kg⁻¹ dung were prepared and deposited on grassland in October 2003. Pats were collected again for analysis 1, 3, 5, and 7 weeks after deposition. Earthworms were collected from the soil around pats at a depth of 0–10 cm. The Megascolecidae, Pheretima (Amynthas) heteropoda and Pheretima (Amynthas) divergens, together accounted for more than 90 and 99% of earthworm individuals and biomass, respectively. Earthworms aggregated around the pats regardless of the ivermectin treatment. Dung-degradation rate was also unaffected by the ivermectin treatments. Dung decomposition appeared to be due mainly to earthworm activity, as dung beetles were rare at this site. These results suggest that ivermectin may have no adverse effects on Megascolecidae activity and on the degradation of cowpats in pastureland sites where earthworms dominate the dung decomposer community.     

Mercury methylation,uptake and bioaccumulation by the earthworm Lumbricus terrestris (Oligochaeta)

To date, most studies about mercury (Hg) methylation and bioaccumulation have focused on aquatic ecosystems. In contrast, information regarding the biogeochemical cycle of Hg in terrestrial ecosystems is scarce. Considering the relevance of earthworms in soils, it is very important to study their role in the bioaccumulation and transformation of Hg species (inorganic Hg, IHg, and monomethylmercury, MeHg). The aim of this experimental study was to compare the uptake and bioaccumulation of MeHg and IHg in the earthworm Lumbricus terrestris exposed to soils freshly spiked with inorganic Hg as well as historically contaminated soils. The study consisted of a 28-day uptake phase in Hg (spiked and natural) contaminated and non-contaminated soils followed by a 14-day depuration phase in non-contaminated soils. Soils were characterized by determining not only Hg concentrations (total Hg, MeHg and acid-labile Hg) but also analysed for other physicochemical parameters that can influence the fate of Hg within the earthworm–soil system. Mercury species were determined in earthworms (whole organism) exposed to Hg contaminated and non-contaminated soils. Mercury availability in soils seems to be the main factor controlling the uptake and bioaccumulation of Hg species because, according to kinetic data, the spiked IHg was more readily assimilated and methylated by earthworms. Bioaccumulation factors (BAFs) for MeHg and total Hg were also higher in spiked than in naturally Hg-contaminated soils. In addition, BAFs for MeHg (ranging from 0.8 to 17.3) were higher than those for total Hg (between 0.02 and 0.62) which suggests that MeHg was more easily bioaccumulated by this earthworm species and also that earthworms may actively contribute to MeHg production in soils.     

Repair of a compacted Oxisol by the earthworm Pontoscolex corethrurus (Glossoscolecidae, Oligochaeta)

The potential of Pontoscolex corethrurus to repair the physical degradation of a compacted Oxisol was studied. The Oxisol from Kingaroy, Queensland, Australia was uniformly packed to four treatments of different bulk densities (0.95, 1.15, 1.25, 1.35 Mg m^–3) in pots of 0.24 m diameter and 0.22 m deep. Each pot was inoculated with 12 earthworms (equivalent to 300 m^–2) and maintained close to field capacity water content for 3 months, after which selected soil physical (dry bulk density, penetration resistance, water infiltration), worm activity (cast production, worm weight) measurements and image analysis were carried out. Results showed that worm numbers were maintained at the initial levels in all the treatments except in the 1.35 Mg m^–3 treatment, where there was a 33% decrease. The weight of surface casts per surviving worm was the greatest in the 1.35 Mg m^–3 treatment compared to the lower density treatments. Final soil density was lessened in all treatments to a depth of 0.2 m. Surface cast production was positively correlated with the percentage reduction in bulk density. The greatest percentage reduction in bulk density was in the 1.35 Mg m^–3 treatment and was equivalent to a doubling of soil aeration (to 18.4%). Penetration resistance to the 0.2-m layer was also reduced and values were less than 2 MPa. Slumping of the surface soil was evident in both the lowest and the highest bulk densities resulting in low rates of water infiltration. Image analysis supported the soil physical properties showing an abundance of both fine pores and worm channels in the three lowest bulk densities, and lesser activity (concentrated in the immediate soil surface) in the 1.35 Mg m^–3 treatment. Received: 6 November 1996     

Population dynamics of the earthworm Amynthas alexandri (Annelida: Megascolecidae) in a Kumaun Himalayan pasture soil

Ecological studies on earthworms were conducted in a Kumaun Himalayan pasture soil. The C:N ratio in the soil declined with increasing depth. A combination of hand-sorting and formalin application was used to sample the earthworms. Three species, Amynthas alexandri, A. diffringens (Megascolecidae), and Eisenia fetida (Lumbricidae) were found. Of the 13310 individuals collected, 99.9% were A. alexandri. The maximum density (138.8 m^-2) and biomass (25.2 g m^-2) were recorded in the wet season. More than 60% of the total earthworm numbers and biomass were recorded at 0–10 cm in depth. The mean yearly ratio of clitellate to aclitellate worms was 1:7.3.     

Uptake and toxicity of copper and zinc for the African earthworm,Eudrilus eugeniae (Oligochaeta)

Growth rate change in earthworms is considered to be a suitable endpoint when determining sublethal effects. In this study we evaluated growth and maturation in the vermicomposting earthworm speciesEudrilus eugeniae as marker of sublethal toxicity of copper and zinc. We also compared routes of uptake. Apart from exposing worms experimentally for 73 days to contaminated food, a series of contact filter paper tests was also performed to determine LD₅₀ for copper and zinc. Both copper and zinc at sublethal concentrations affected growth and maturation in worms exposed to contaminated food. These worms had a copper content of 34.5 μg g^?1 after 73 days and a zinc content of 184.9 μg g^?1, showing a differential uptake. Copper was more toxic than zinc. Also in the contact test worms did take up more zinc than copper and the LD₅₀ (48 h) for copper was 0.011 mg cm^?2 and for zinc 0.066 mg cm^?2, which translated to body burdens of 6 μg g^?1 for copper and 131 μg g^?1 for zinc. Indications were that a regulatory mechanism existed for both metals. Both metals were taken up through the body wall at a relatively fast rate. This study indicated that the skin was the major route of metal uptake. This study also showed a poor relation between the two types of tests for purposes of evaluating lethality of zinc and copper.     

Taxonomic status and intraspecific phylogeography of two sibling species of Metaphire (Oligochaeta: Megascolecidae) in Taiwan

In this study the synonymy of Amynthas formosae (Michaelsen, 1922) and A. yuhsii (Tsai, 1964) are reevaluated and the intraspecific phylogeography between them is studied. The morphological comparison and phylogenetic analysis based on cytochrome c oxidase subunit I suggest that A. formosae and A. yuhsii are not synonyms and both of them belong to Metaphire. The phylogeographic analysis suggests that the formation of mountains and rivers during the uplift of the Western Foothills in Taiwan comprised the vicariance events responsible for the intraspecific genetic differentiation between these two species.     

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.     

Modifications to a defined medium for the study of the biology and toxicology of the earthworm Eisenia fetida (Oligochaeta)

Defined and standardised media for the investigation of growth and reproduction of earthworms from a juvenile stage have been developed, but still retain a measure of components that are difficult to characterise completely. A defined medium, based on vermiculate, cellulose, humic acid and other components that are commercially available, and that supports growth and reproduction of E. fetida, added as juveniles, has previously been developed. However, one of the nutrients is not available anymore, and modifications were required. A series of various combinations were evaluated using commercially available nutrients such as fatty acids, organic phosphates and oxy-humic acids. All of the media supported growth (excepting one containing creatinine), but cocoons were only produced in some. It was shown that the growth and reproduction of E. fetida could be studied in a defined medium for up to 70 days (starting with 20-day old juveniles) without additional feeding. The various defined media reported here can be adopted to study specific aspects of earthworm biology and ecotoxicology in the laboratory, but would not replace the existing OECD methods.     

Uptake and toxicity of copper and zinc for the African earthworm,Eudrilus eugeniae (Oligochaeta)

Growth rate change in earthworms is considered to be a suitable endpoint when determining sublethal effects. In this study we evaluated growth and maturation in the vermicomposting earthworm speciesEudrilus eugeniae as marker of sublethal toxicity of copper and zinc. We also compared routes of uptake. Apart from exposing worms experimentally for 73 days to contaminated food, a series of contact filter paper tests was also performed to determine LD₅₀ for copper and zinc. Both copper and zinc at sublethal concentrations affected growth and maturation in worms exposed to contaminated food. These worms had a copper content of 34.5 g g^–1 after 73 days and a zinc content of 184.9 g g^–1, showing a differential uptake. Copper was more toxic than zinc. Also in the contact test worms did take up more zinc than copper and the LD₅₀ (48 h) for copper was 0.011 mg cm^–2 and for zinc 0.066 mg cm^–2, which translated to body burdens of 6 g g^–1 for copper and 131 g g^–1 for zinc. Indications were that a regulatory mechanism existed for both metals. Both metals were taken up through the body wall at a relatively fast rate. This study indicated that the skin was the major route of metal uptake. This study also showed a poor relation between the two types of tests for purposes of evaluating lethality of zinc and copper.     

The contribution of endogenous cellulase to the cellulose digestion in the gut of earthworm (Pheretima hilgendorfi: Megascolecidae)

Cellulase activity has been detected in the digestive tract of earthworms. However, it has not been well clarified whether the origin of those cellulases are the earthworm themselves or the symbionts. In our study, zymogram analysis suggests that one cellulase (endo-β-1,4-glucanase, EC3.2.1.4) mainly works to digest cellulose in Pheretima hilgendorfi. To identify the cellulase in P. hilgendorfi, we carried out cDNA cloning of the cellulase gene from the digestive tract. A novel cellulase gene was identified from the gut of earthworm. The cDNA encoding cellulase of P. hilgendorfi (phhEG) is 1606 bp with an open reading frame encoding a protein of 449 amino acid residues. The deduced amino acid sequence of P. hilgendorfi cellulase showed higher homology to invertebrate cellulases than bacterium cellulases belonging to the glycosyl hydrolase family (GHF) 9. The phhEG gene was detected in intestinal epithelium cell of midforegut using Northern blot and in situ hybridization. Similarly, specific cellulase activity against carboxymethyl cellulose (CMC) was significantly higher in midforegut tissue. Recombinant phhEG produced by wheat germ cell-free protein synthesis system had a cellulase activity which degrade CMC. In zymogram analysis, the molecular size of cellulase was detected as a single band of 51 kDa from the whole gut contents extracts of P. hilgendorfi, and was very similar to the predicted molecular size of the mature phhEG protein. These results strongly suggested that the earthworm has the capacity to produce the endogenous and functional cellulase around the midforegut, and use this cellulase for their cellulose digestion with the support of intestinal caecum.     

Influence of animal wastes on growth and reproduction of the African earthworm species Eudrilus eugeniae (Oligochaeta)

The growth and reproduction of Eudrilus eugeniae were evaluated in four animal species wastes under laboratory conditions. Two hatchlings were introduced in 100 g of each animal waste i.e. cow, sheep, pig, and chicken after 15 days of pre-composting. Biomass gain, mortality, sexual maturity, and cocoons production were monitored periodically for 21 weeks. No mortality was observed in any waste. The maximum weight gain per worm and the highest growth rate per worm per week were obtained in chicken waste. Net biomass gain per worm were 1.01 ± 0.52 g, 1.318 ± 0.07 g, 0.87 ± 0.1 g, and 1.69 ± 0.15 g respectively for cow, sheep, pig, and chicken wastes. The highest number of cocoons produced per worm per day was obtained in chicken waste followed in decreasing order by sheep, cow, and pig waste. The mean number of cocoons produced per worm per day in chicken waste was 40.87% greater than these produced per day in pig waste.Among the four animal species, chicken, sheep, and cow were the most favourable wastes for the growth and reproduction of E. eugeniae, and hence can be recommended as feed materials in large scale vermicomposting facilities.     

The influence of feeding patterns on growth and reproduction of the vermicomposting earthworm Eisenia fetida (Oligochaeta)

Summary Observations in outdoor culture beds indicated that food availability and frequency of feeding influenced worm density. In order to study the role of feeding status on the growth and reproduction of Eisenia fetida, pre-clitellate specimens were kept for 180 days under controlled conditions. A control group was regularly provided with freshly produced cattle manure while the experimental groups were fed only sporadically and at some stage even starved by removing some of the substrate. Worm growth, maturation, and cocoon production were monitored. The role of food availability was highlighted by this study. Both worm growth and cocoon production were correlated closely with the feeding pattern that was followed. This study also showed that freshly produced, urine-free, cattle manure proved an excellent food source provided it was added in such a way as to prevent the development of anaerobic conditions. Regular feeding gave high growth and reproduction rates.     

Effect of organic manure and the endogeic earthworm Pontoscolex corethrurus (Oligochaeta: Glossoscolecidae) on soil fertility and bean production

A biofertilisation assay was conducted in Maripasoula (French Guiana), testing the effects of three different organic amendments (manioc peels, sawdust and wood charcoal) and the inoculation of the endogeic earthworm Pontoscolex corethrurus on pod production of Vigna unguiculata sesquipedalis and on soil chemical properties (pH, C, N, total and exchangeable P and K). Pod production was highest with manioc peels as available P increased in the soil. Wood charcoal also had a beneficial effect on pod production as it decreased acidity and increased the C:N ratio in the soil. In sawdust-amended soil, pod production did not differ from that in unamended soil. Inoculation of earthworms at a density of 80 sub-adults m^-2 did not significantly affect either pod production or soil nutrient content directly, although it increased the positive effect of manioc peels on pod production. Soil nutrient content, pod production and earthworm density at the end of the experiment were negatively correlated with soil moisture and positively with each other. Despite the strong effect of moisture, this assay demonstrated an interaction between the earthworm P. corethrurus and the legume V. unguiculata sesquipedalis mediated by soil nutrient content and organic matter inputs. We conclude that manioc peels improved soil P availability and were an interesting amendment for legume crops. We discuss also the effect of earthworm inoculation.     

Adaptive strategies of Pontoscolex corethrurus (Glossoscolecidae,Oligochaeta), a peregrine geophagous earthworm of the humid tropics

Summary Pontoscolex corethrurus is a medium-sized geophagous earthworm species which has invaded most cultivated land in the humid tropics. It is generally found in gardens, cropland and fallowland, where it has been introduced accidentally by man. The species has quite narrow microclimatic requirements. Reproduction only occurs at 23°–27°C, and the worms are fully active only where soil moisture is well above field capacity (pF 2.5). This limitation is balanced by the ability to live in a great Variety of soils differing in pH, organic matter content and texture. The demographic profile is typically of the r type, which gives populations a colonization capacity greater than that of comparable native species. This can be explained by the limited size of individuals and the great efficiency of their mutualist digestion system, in association with the free soil microflora. As a result, growth is fast and a great amount of energy may be invested in reproduction, which is made even more efficient by parthenogenesis.     

The influence of soil characteristics on the toxicity of four chemicals to the earthworm Eisenia fetida andrei (Oligochaeta)

Summary The acute toxicity of Cd (chloride), chloroacetamide, 3,4-dichloroaniline and pentachlorophenol to the earthworm Eisenia fetida andrei was determined using the OECD (1984) artificial soil and contact testing procedures. To investigate the influence of two soil characteristics (pH and organic-matter content), the toxicity of the chemicals was also determined in two natural sandy soils. It is concluded that the filter-paper contact test cannot be recommended to predict earthworm toxicity of these chemicals in soil. Toxicity in soil was influenced by both pH and organic-matter content. Differences between LC₅₀ values in the high-organic-matter artificial soil and in an acid, low-organic-matter sandy soil were, however, not greater than a factor of 3–4. The results of this study therefore support the use of a well-defined artificial soil substrate for standardized earthworm toxicity tests.