Nematodes, or C. elegans, are millimeter-long (one twenty-fifth of an inch) worms that live in soil and eat bacteria. Because the same genes are found in many animals, nematodes, mice, zebrafish and fruit flies often are used as models for humans in research.
Nematode worms lack eyes, so attraction is based only on the sense of smell. There are no true females and only one in 500 nematodes is male. Most are hermaphrodites, with both male and female organs. Jorgensen and White loosely refer to hermaphrodites as females because they produce offspring.
A hermaphrodite makes both eggs and sperm, Jorgensen says. She doesnt need to mate [with a male] to have progeny, but can fertilize her own eggs. Most of the time, the hermaphrodites do not mate. But if they mate, instead of having 200 progeny, they can have 1,200 progeny.
Nematodes are few and far between in soil. So natural selection favored hermaphroditic worms because when they found an abundant food source, they were able to feast and make babies even if no males were nearby, Jorgensen says.
Male nematodes must find hermaphrodites if they are to reproduce, and they find them by smelling their sex-attractant odors or pheromones.
The Mind of a Worm is Sexualized
Jorgensen says the study looked at three possibilities, namely, whether male attraction to hermaphrodites results from:
-- Four accessory or extra smell-related nerve cells named CEM neurons that are found only in male brains. The worms gain these neurons during their version of puberty, their fourth larval stage.
-- Four core or basic smell-related nerve cells two named AWC and two named AWA found in both males and hermaphrodites.
-- Both the accessory and core neurons.
The answer was that male attraction involves the combination of both accessory and core nerve cells. The involvement of the core neurons was a surprise.
|Contact: Lee Siegel|
University of Utah