Oxidus gracilis: First lab tractable myriapod model

Myriapods (millipedes and centipedes), unlike all other arthropods, insects (beetles, etc.), crustaceans (shrimps, etc.), and chelicerates (spiders, etc.), do not have a single, lab-tractable model. This makes them the least studied group of arthropods in evo-devo. This is unfortunate since myriapods display many fascinating traits such as silk-producing spinnerets, cyanide-based defensive glands, a mode of segmentation that results in hundreds of body segments, and unique metamorphosis of their reproductive structures. In addition, myriapods occupy a phylogenetically important position at the divergence between chelicerates and the rest of the arthropods (myriapods, crustaceans, insects; collectively called the mandibulates) and thus there is much interest in the evolution of their neural patterning, tracheal system, eyes, and in identifying the first stem myriapods.

We are developing the first myriapod lab-tractable model system using the greenhouse millipede Oxidus gracilis. Several other myriapod species have been attempted to date. However, none of these are ideal lab animals because they do not survive in lab conditions; they do not breed year-round; and/or they take several years to reach sexual maturity.

In contrast, Oxidus gracilis:

Animal collection: Oxidus gracilis adults have been collected from Massachusetts, Washington DC, and Wesbrook, Vancouver. However, they are found in greenhouses globally so establishing a population is not difficult.

Animal rearing conditions: Shoebox-sized glass containers with damp leaf litter and mulch. This is sufficient to maintain the millipedes for many weeks, though they can be supplemented with fish food for extra protein. This is especially important for cages with juveniles. Substrate should be changed every 4-6 months.

Pest control: The biggest issue with maintaining a colony has been with pest control. Nematode and fugus populations can be easily controlled by adding springtails as a biological control agent. The larger issue is phoretic mites. The species of these mites is unknown. All we know is that once the millipedes get the larval stages attached to their legs, the colony will die within a couple of weeks. To combat this, we have developed a sterile protocol when working with the millipedes and have successfully isolated a mite-free cage of juvenile millipedes (knock on wood). A new colony of adults was established from pedes collected in Richmond, BC but these have since been infested with mites, despite our “mite dilution” protocol. The idea behind this protocol was to change the adult’s cage and substrate every 4 days, transferring them to a new clean enclosure with freeze sterilized soil. We hoped that if we could catch the mites in their non-phoretic phase, discarding them with the old substrate, we could eventually dilute the population to unsustainable levels. We hope that the juveniles currently in the mite-free cage will reach sexual maturity and be able to maintain the colony. If not, more adult pedes will be collected this summer.

Diet: Hardwood mulch substrate above supplemented 1x/week with fish food pellets.

Husbandry: Animals mate readily once correct conditions are established. Males mate guard females by sitting on top of and holding the female (amplexus). Mating can take several hours.

Embryo collection and rearing: Clutches of >200 embryos are laid 1-2cm deep in mulch substrate above. Most clutches are laid on the bottom of the container and can be located by holding the container aloft and looking underneath, otherwise, clutches can be located by gently overturning mulch with a probe.