One of the larger forms of Pristionchus, which eats other nematodesTheir shapes are so different that they look like five different species.But genetic studies have shown single species of nematode worm, newly discovered inside figs, can develop into five distinct forms. It is a striking example of physical divergence without genetic divergence.“We were shocked,” says team member Erik Ragsdale of the University of Indiana. “It is remarkable and unusual.”Young Pristionchus nematodes hitch a ride to new figs on the wasps that fertilise the figs. If you look inside the fig soon after the wasps arrive, only a small form of the nematode can be found. It has a simple tube-like mouth for feeding on microbes.
Three forms have teeth
But the offspring of these colonists can develop into five distinct forms: two that feed on microbes and three larger ones with bigger mouths equipped with rows of teeth, for catching other species of nematodes. “They have different ecological roles,” Ragsdale says.Many animals, particularly insects, can develop into different forms depending on the environment, season or social cues – a phenomenon known as polyphenism. The white winter coats of many animals are a familiar example.More dramatic examples include the moth Nemoria arizonaria, whose caterpillars grow to resemble oak catkins if they hatch in spring but oak twigs if they hatch later on.
Cannibal forms
In other animals including a few fish, birds, frogs and salamanders, there are distinct cannibalistic phenotypes with features such as larger mouths for eating their peers. And some arachnids have distinct forms armed with different weapons.