Ecology and mouth dimorphism in Pristionchus pacificus. d–f, P. pacificus can have one of two distinct morphologies, eurystomatous (d, e) or stenostomatous (f). Eurystomatous worms have a subventral right denticle (d, red outline), and the dorsal left denticle (e, f, blue outline) is bigger and claw-like unlike in stenostomatous worms.
Credit: Image courtesy of G. Bento, A. Ogawa & R. J. Sommer
SYDNEY: In a bizarre evolutionary twist, when the commonly studied bacteria-eating worm Pristionchus pacificus is hungry it grows a different mouth, complete with teeth, and starts eating other worms.
It was a surprise discovery. Gilberto Bento and his colleagues at the Max-Planck Institute for Developmental Biology in Germany were watching nemotode worms under a microscope and saw P. pacificus bite into another worm.
This may not sound particularly thrilling, but until then the commonly studied P. pacificus worm was thought to eat only bacteria.
An unexpected cannibal
The attacking worm then consumed the other worm's insides as they spewed out of its body, according to the researchers, who published their study in the journal Nature.
The researchers had to find out whether there was a genetic difference. "If the two morphologies are there only because of a different genetic background then... we should be able to produce strains (races) that show only one or the other morph but not both," said Bento.
When they starved the worms, Bento and his colleagues found that 84% of the worm developed teeth, making them capable of eating other worms.
Hungry hungry nemotodes
When they didn't starve the worms, only 32% developed teeth. Instead, the worm developed a narrow long cavity for consuming bacteria.
"[This] shows that the mouth morphology has to have an environmental basis and therefore is a polyphenism," said Bento.
'Polyphenism' - when the physical expression of a gene is influenced by environmental factors - is found throughout the animal kingdom, such as in crocodiles, where sex determination is affected by the temperature of the nest.
