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April 29, 2009
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Scientists report flipping worms’ sexual preferences
Oct. 25, 2007
Courtesy University of Utah
and World Science staff
Biologists have genetically tweaked roundworms to make them attracted to worms of the same sex—part of a study, they say, that shows sexual orientation is
genetically wired in the creatures’ brains. The nematode
worm C. elegans. (Courtesy free.ed.gov)
Sex preference seems to arise in “brain circuits common to both sexes of worms,” said University of Utah biologist Erik Jorgensen, one of the researchers in the wide-ranging study.
“We cannot say what this means for human sexual orientation, but it raises the possibility that sexual preference is wired in the brain… Humans are subject to evolutionary forces just like worms.”
The work echoes research with fruit flies in 2005, in which the flip of a genetic
switch induced females to make amorous displays toward other females. But there were several differences.
The millimeter-long roundworm C. elegans lives in soil and eats bacteria. Like fruit flies, it’s often used in basic genetic research, as many of its genes are thought to be related to human genes. The worm lacks eyes, so attraction is based on smell. There are no true females and only one in 500 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,” and can thus fertilize
itself, though this creates fewer offspring, Jorgensen said. The ability probably evolved because roundworms are few and far between in soil, so mates aren’t always available, he added. Males, though, must find hermaphrodites to reproduce, and find them by smell.
“We took the hermaphrodite brain and we activated the genes that determine maleness,” but only in the brain, Jorgensen said. The result: “They look like girls, but act and think like boys,” said biologist Jamie White of the university. White is first author of a paper on the findings to appear in the Nov. 6, and the Oct. 25 advance online, issues of the research journal
Current Biology.
The artificially activated gene, called fem-3, normally makes the body develop male structures such as a tail, which male worms use to copulate, White said. With fem-3 switched on only in the brain, hermaphrodites kept their bodies unchanged; but they were attracted to other hermaphrodites, crawling toward their sexual chemical signals, the investigators said.
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Biologists have genetically tweaked roundworms to make them attracted to worms of the same sex—part of a study, they say, that shows sexual orientation is wired in the creatures’ brains. The preference seems to arise in “brain circuits common to both sexes of worms,” said University of Utah biologist Erik Jorgensen, one of the researchers in the wide-ranging study. “We cannot say what this means for human sexual orientation, but it raises the possibility that sexual preference is wired in the brain… Humans are subject to evolutionary forces just like worms.” The work echoes research done with fruit flies in 2005, in which female flies were induced to make amorous displays toward other females with the flip of a genetic switch. But there were several differences. The millimeter-long roundworm C. elegans lives in soil and eats bacteria. Like fruit flies, it’s often used in basic genetic research, as many of its genes are thought to be related to human genes. The worm lacks eyes, so attraction is based on smell. There are no true females and only one in 500 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,” and can thus mate with herself, though this results in fewer offspring, Jorgensen said. The ability probably evolved because roundworms are few and far between in soil, so mates aren’t always available, he added. Males, though, must find hermaphrodites to reproduce, and find them by smell. “We took the hermaphrodite brain and we activated the genes that determine maleness,” but only in the brain, Jorgensen said. The result: “They look like girls, but act and think like boys,” said biologist Jamie White of the university. White is first author of a paper on the findings to appear in the Nov. 6, and the Oct. 25 advance online, issues of the research journal Current Biology. The artificially activated gene, called fem-3, normally makes the body develop male structures such as a tail, which male worms use to copulate, White said. With fem-3 switched on only in the brain, hermaphrodites kept their bodies unchanged; but they were attracted to other hermaphrodites, crawling toward their sexual chemical signals, the investigators said.