Panagrellus redivivus
This species is ovoviviparous. Under standard conditions (Hechler 1970) embryogenesis takes ~20 hr, producing a first-stage juvenile (L1) within the egg shell. The L1 undergoes a molt giving rise to a second-stage juvenile (L2), which emerges from the egg shell and is actively expelled by the female from the oviduct via the vulva. Under adverse environmental conditions, such as high population densities, low nutrient levels, or the presence of some toxicants, the L2 animals are not expelled, but remain in the oviduct where they devour the interal tissue of the female, including eggs. These L2 animals may go through several developmental stages during this process of endotokia matricida before emerging through the cuticle of dead female and entering the environment. Normally, however, the L2 is the first free-swimming stage, readily isolated from mass cultures. L2 animals held in a salt solution will not grow or develop. In the presence nutrients, the L2 grows and molts to the third juvenile stage (L3). The L3 grows and molts to the fourth juvenile stage (L4), which under appropriate conditions, grows and molts to the adult stage. The molts require bursts of RNA and protein biosynthesis (Boroditsky and Samoiloff 1973). The major criterion for determination of stage is length. The L2 to L3 molt occurs at a length of ~350 um, which represents the upper limit for the length of the L2 stage. The L3 to L4 and L4 to adult molts occur at ~550 and 850 um, respectively. Adults may reach lengths of 1800 um. During postembryonic development the number of somatic nuclei remains nearly constant, with ~500 somatic cells in the organism (Sim and Pasternak 1970). The duration of postembyonic development, from L2 to adult, varies with culture conditions. (ref. ID; 868)
[ref. ID; 868]
Test systems
Developmental assay and mutagenesis assay
Strains
The standard "wild-type" strain C-15 obtained by two rounds of 15 generations of sib-sib matings. The synchronous L2 animlas using which, 150-300 gravid females are transferred to M9 buffer, and the L2 progeny harvested after 14-16 hr.
Toxicants/concentrations
28 known mutagens, putative carcinogens, and heavy metal compounds. Concentration (mol/L) 10E-3 ~ 10E-8.
- Known carcinogens. 2-acetamidofluorine, Acrylonitrile, Aflatoxin B, Aminobiphenyl, Benzene, Benzyl chloride, Bromouracil, Chloromethyl ethyl ether, Dimethylbenzanthracene, Ethyl methanesulfonate, 3-methylcholanthrine, Methyl methanesulfonate, Proflavine, beta-Propiolactone, Vinyl chloride.
- Putative carcinogens. Chloroform, Dibutyl pthalate (misspelling? phthalate), Dichloromethane, Hexachlorobenzene, Methoxychlor, Phenacetin.
- Metals. Cadimum chloride, Cesium chloride, Mercuric chloride, Methyl mercury, Nickel oxide, Selenium oxide, Vanadium pentoxide.
Test design
- Developmental assay: Ten second-stage juveniles (L2) are placed in each of the series of 2.5 ml autoanalyzer cups containing 0.5 mL M9-yeast-cholesterol medium with or without a known concentration of the agent tested. 3 replications. 22 degrees C, 9 hr.
- Mutagenesis assay: Individual L2 females homozygous for the X-linked mutation b7 are grown for 120 h in autoanalyzer cups containing M9-yeast-chloesterol medium was tested agent. After the growth period, the virgin females are washed, and transferred to an agar plate and mated with males from strain S-15. One hundred of the female progeny are collected as larvae, grown up on M9-yeast-chloesterol medium and mated to wild-type (C-15) males. Each gravid female is transferred to 0.2 mL M9 medium in Falcon 96 well test plates.
Measurements/observations
- Developmental assay: The numbers of survivors and size distribution.
- Mutagenesis assay: The presence of the b7 phenotype.
[ref. ID; 6957]
Test system
Inhibition of estradiol binding
Strains
Axenically. Culture liquid medium containing 3 g yeast extract, 4 g soy peptone, 10 ml HLE (heat liver extract), and 90 ml distilled water.
Toxicants
Dieldrin, Nonylphenol, Toxaphene, Dieldrin+Nonylphenol, Dieldrin+Toxaphene, Nonylphenol+Toxaphene
Test design
Radioimmunoassay [125]I-17beta-estradiol.
P. redivivus were cultured in 2 ml HLE along with the chemical doses for 3-7 days in 20-ml vials.
Measurements/observations
Male and female counts.
Evaluations
Gender ratios, fecundity.