M Model Organisms
There are tw o sexes - self-fertilizing herm aphrodites and males (Figure 1). M ost adult worms are herm aphrodites, w ith males occurring spontaneously at a rate of <0.5% . However, the progeny of a mating between males and her m aphrodites are 50% of each sex. The herm aphrodite lays em bryonated eggs which hatch to give the first larval stage (LI), which then moults through three further larval stages (L2-L4), with the L4 finally m oulting into adult worms (Figure 2). The generation time is about 3 days at 25°C and adult herm aphrodites live for about 10-15 days. There is also an alternative L3 m orph called the dauer larva, which is morphologically, behaviourally and physiologically dis tinct from the “norm al” L3. It develops under conditions of crowding and limited food supply and, biologically, it is the resistant, dispersive stage of the life cycle.