Feeding and Care of several species of terrestrial isopods.
The information which follows is based mainly on two species of terrestrial isopods - Armadillidium vulgares and Porcellio scaber. The organisms are easily captured near homes and schools and are relatively easy to care for in captivity. The cited papers are just a few of many which provide research results related to the feeding and environmental needs of the isopods. The papers reference or decribe other techniques for rearing the isopods in controlled environments. Students may develop their own investigations after reading some of the papers.
Containers for keeping the isopods can vary, depending more on the intended use. Researchers use a layer of plaster of paris in the bottom of containers as a means to maintain humidity and easier removal of fecal material during experiments. If you wish to only observe the animals as they interact and produce young, potting soil can be used. In either case, as you will read below, there must be soil bacterial present on the food items and a pH above 4.9 to permit the bacteria to break down leaf litter. The isopods rely on the soil bacteria as well as cultures of bacteria in the posterior end of their reproductive tract to break down cellulose and some toxic compounds in the leaf litter that they eat.
The young are copophagic, which means they consume the fecal material left by adults. This is necessary for giving them the gut bacterial they need as well as nutrients released by the bacteria. They are much more sensitive to humidity levels and there is a large mortality in young.
The container housing the isopods need to be places in sheltered areas, away from direct sunlight and heat. Temperatures should stay in the range of 15C to 19C. Outside these limits will stress the animals. The isopods live 3 to 4 years with offspring being produced in the second, third and fourth year, depending on a varity of environmental and nutritional conditions. The same conditions will also affect the number of offspring produced at one time as well as the size of the female.
The type of cover used on the container will affect the humidity level. Some experimentation may be needed to get the conditions right for the particular area you are keeping the isopods.
Terrestrial isopods have some requirements left over from their aquatic, crustacean ancestry. Moisture as humidity and pH influence survival of juveniles and adults. There can be too much or too little moisture. The pH level plays a role in the diet (Zimmer and Topp, 1997). Food requirements vary not only between species but between life stages of same species. The later is advantageous in reducing competition between juveniles and adults for nutrients (Zimmer, M. and Topp, W. 2000).
The amount of tannins, phenolics and other secondary chemicals, which plants produce, also affect the quantity of plant material consumed in the litter and the survivability of some isopods species (Zimmer, M. and Topp, W. 2000) . Microbiotic organinisms in the litter environment play a role in the successful feeding in at least two ways. One is that microorganisms break down cellulose and some of the toxins in the litter. Second, the microbes are a direct food source for some species of isopods which also make use of bacterial enzymes to break down toxic molecules and cellulose in the gut (Zimmer, M. and Topp, W.1998).
The chemical influences on isopod diet, make some plant species more beneficial to isopods. The carbon to nitrogen ratio factors into the success of a particular species survival in an area. Higher nitrogen seems to benefit some life stages of some species, as do the microbes. The significance of these various factors seem to vary between life stages of sympatric species (Zimmer, M. and Topp, W. 2000).
A. vulgares exhibits phenotypic plasticity ( Helden, Alvin J. and Hassall, Mark, 1998) with respect to temperatrue and food quality as observed in growth, rate, size of the young and the adults and first time for young production. This species will grow larger and have young the second year if the temperature and food quality are optimum ( deciduous leaf litter). If the food quality is low, monocots, females may not produce young until the third year and will be smaller in size when the young are produced. If the temperature is low, it will increase the time before producing young to 3 years. Rushton and Hassall., (1983) showed that adults grew better on standing, dead material than decayed material (p<0.0001). Juveniles, seem to be able to make use of monocotyledonous material and show some growth whereas the adults did not show significant growth. Combining two good quality foods resulted in better growth of juveniles than the individual foods. Given a choice, A. vulgares will choose dicot food sources over monocots (Rushton and Hassall., 1983). In one case they chose death over eating monocots. They were equalling attracted to filter paper and monocots in a second case.
Studies with Porcellio scaber showed a complex interaction between soil bacteria, pH, leaf toughness, nitrogen carbon ratio, tannin and phenolic content. Soil microbes do well in environments with pH values above 4.9. P. scaber showed the greatest longevity and the largest number of offspring at the same pH levels. Plant species also made a difference with the most success on maple and lowest on oak. There was some influence from cellulolytic activity on the leaf litter with greater success on litter with higher activity. (Zimmer, M. and Topp, W.,1997).
This work on food quality and preferences have been done in Europe. Students might attempt similar experiments on food sources found in local environments to see if they get similar results.
|Helden, Alvin J. and Hassall, Mark, 1998. Phenotypic plasticity in growth and development rates or Armadillidium vulgares (Isopoda: Oniscidea). Isreal J. of Zoology, 44:379-394
|Rushton, P. and Hassall, M., 1983, The effects of food quality on the life history parameters of the terrestrial isopod (Armadillidium vulgare(Latreille))., Oecology. 57:257-261.
|Rushton, P. and Hassall, M., 1983, Food and feeding rates of the terrestrial isopod (Armadillidium vulgare(Latreille))., Oecology. 57:415-419.
|Zimmer, M. and Topp, W.,1997. Does leaf litter quality influence population parameters of the common woodlouse, Porcellio scaber (Crustacea: Isopoda)?, Biol. Fertil. Soils 24:435-441
|Zimmer, M. and Topp, W.,1997. Microorganisms and cellulose digestion in the gut of the woodlouse Porcellio scaber. J of Chemical Ecology, 24(8):1397-1408.
|Zimmer, M. and Topp, W.,2000. Species-specific utilization of food sources by sympatric woodlice (Isopoda: Oniscidea)., J of Animal Ecology, 69: 1071-1082.
Under construction. References and more detail will be forthcoming. 03/25/2004