Experimental organisms

Lumbricidae

Earthworms are members of the phylum Annelida, the class Oligochaeta and the order Opistophora. Although there’s no generally accepted standpoint in further classification, based on latest research, 16 families are suggested, of which 6 include aquatic and semi-aquatic species, while the remaining 10 families consist of dryland species known as earthworms. Most European species and all species present in Croatia are members of the family Lumbricidae. Earthworms are generally divided into three morpho-ecologic categories: epigeic, endogeic and anecic earthworms. Epigeic earthworms can be found under layers of fallen leaves, rotten logs, in the upper layer of the soil and in areas with higher concentration of organic matter. Endogeic species usually lack pigmentation and dig horizontal passages in the soil. They don’t visit the surface. Anecic species, represented by Lumbricus terrestris, dig vertical corridors in the soil, while they feed and reproduce on the surface.

Eisenia fetida (Bouché) is the most commonly bred earthworm species and, due to it’s accessibility, a standard species used in toxicological and ecotoxicological soil research. This species can be found in environments with high levels of organic matter like compost and piles of manure. This epigeic species is bred and reproduced easily.

Enchytraeidae

The family Enchytraeidae includes 27 genera and approximately 500 species, however, new species are determined every year. Most species are hermaphrodites, still there are parthenogenetic species as well as those that reproduce by fragmentation. Enchytraeidae are widely distributed between the Arctic and tropical regions, but the knowledge on their distribution, productivity and activity is mostly limited on the European species. Enchytraeidae are directly and indirectly involved in the process of degradation and nutrient mineralization. Directly by consuming large amounts of organic matter and indirectly by creating structures in soil and affecting activity and functioning of microbial communities through their feeding. Enchytraeidae influence is particularly important in acidic and nutrient-poor ecosystems, like peatlands in the temperate zone and boreal forests, where this family represents a dominant group of soil fauna in terms of biomass.

Annelids from the genus Enchytraeus that live in the soil, represent an ecologically relevant group of species in terms of ecotoxicological research. While Enchytraeidae commonly share their habitat with earthworms, they can also be found in soils where earthworms are not present. Enchytraeidae can be used in laboratory research, as well as in semi-field and field research. From the practical point of view, Enchytraeidae are easy to breed and operate with. They also have a shorter generation cycle than earthworms do. The duration of reproduction tests with Enchytraeidae is 4-6 weeks, while it’s 8 weeks in the case of using earthworms (Eisenia fetida). Two most commonly used species in the mentioned type of research are Enchytraeus albidus and Enchytraeus crypticus.

Enchytraeus albidus is one of the biggest species of Enchytraeidae, with size reaching up to 35 mm. It’s widely distributed around the world. This species is easily grown and bred in various organic substrates. The life cycle is short and individuals reach sexual maturity at age between 33 days (at 18°C) and 74 days (at 12°C). Tests require cultures that have spent at least five weeks (one reproductive cycle) in the laboratory.

Enchytraeus crypticus is easily grown and bred. It’s manipulation is somewhat harder that that of Enchytraeus albidus due to it’s smaller size.

Collembola (Springtails)

Collembola, specimen of soil fauna, represent an ecologically relevant group used in ecotoxicological research. A widely distributed order of arthropods from the class Entognatha whose members live in all possible geographic and climate conditions. Their thin exoskeleton is highly permeable by air and water. For their ecology, they’re significantly different from earthworms and Enchytraeidae, which are also used in determining the effects of chemicals in the soil.

The average density of their populations is 105 individuals/m2. Adult individuals are between 0.5 and 5 mm. Their contribution in soil-respiration is approximated to 1% to 5%. They play a key role in regulation of soil processes by consuming microorganisms, while being relevant prey of numerous epigeic and endogeic invertebrates, such as maggots, centipedes, spiders, beetles and weevils. They also contribute to degradation processes in acidic soils due to the absence of earthworms and millipedes.

Folsomia candida is a common and widespread species of springtails that occurs in soils throughout the world as a member of mesofauna. Although it’s not common in native soils, it can be found in humus rich soils. It lacks pigments as well as eyes. F. candida reproduces by parthenogenesis and is easily bred.