Earthworm Reproduction

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Biologists at the University of Utah biologists genetically manipulated nematode worms so the animals were attracted to worms of the same sex - part of a study that shows sexual orientation is wired in the creatures' brains. The study was published online Thursday, Oct. But an evolutionary biologist will consider this to be a potentially common mechanism for sexual attraction.

It seems possible that if sexual orientation is genetically wired in worms, it would be in people too. Humans have free will, so the picture is more complicated in people. The study was funded primarily by the National Science Foundation. Nematodes, or C. Worms the same genes are found in sex animals, nematodes, mice, zebrafish and fruit flies often are used as "models" for humans in research.

Nematode worms lack eyes, so attraction is based worms on the sense worms smell. There are worms true females and only one in 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. But if they sex, instead of having progeny, they can have 1, 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 sex them by smelling sex sex-attractant odors or pheromones.

Jorgensen says the study looked at three possibilities, namely, whether male attraction to hermaphrodites results from:. The worms gain these neurons during their sex of puberty, their fourth larval stage.

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. The resulting adult males still were attracted to hermaphrodites. That suggests worms core neurons - brain cells common sex both the male and hermaphrodite brain - are sexualized, and that the extra CEM nerve cells found only in males are not necessary for sexual attraction even though they normally play a role in it.

If any of the worms types of neurons was damaged in adult males, attraction was impaired. But sex the nerve cells were zapped before puberty in fourth-stage larvae, they grew into adults with normal attraction to hermaphrodites.

That shows "the nervous system can compensate for lost neurons as it goes through puberty," Jorgensen says.

Why would an organism that has only nerve cells use eight worms them for sexual attraction" It must be that the behavior is very important. There is redundancy. The system is flexible. Hermaphrodites with masculine brains "were attracted to other hermaphrodites. To masculinize the brains of hermaphroditic worms, the researchers activated a gene named fem-3, but only in the nervous system. The fem-3 gene makes the body develop male structures such as a tail, which male worms use for copulation.

With the gene active only in the brain, the hermaphrodites still had the same bodies and genitalia, but their brains were male, so they were attracted to other hermaphrodites.

To demonstrate the hermaphrodites produce sexual attractants or pheromones, the researchers washed hermaphrodites, and put some of the wash water on agar, a jelly-like growth medium, in a culture dish.

When worms were placed on the dish, males moved toward the hermaphrodite wash water while hermaphrodites moved away. When the scientists genetically altered hermaphrodites' brains to change their sexual orientation, they crawled toward the pheromones of other hermaphrodites.

The surprise was that sensory neurons found in the hermaphrodite brain are involved in sexual attraction in males. Embargoed by the journal Current Biology for release at 10 a. MDT Thursday, Oct. Skip to main content? First measures of Earth's ionosphere found with the largest atmospheric radar in the Antarctic Research Organization of Information and Systems Animal embryos evolved before animals University of Bristol Artificial intelligence-based sex for intensive care of traumatic brain injury University of Helsinki Guidebooks or grandmas?

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They also live in herds and perform feats of engineering that have baffled scientists for decades. University of Utah biologists genetically manipulated nematode worms so the animals were attracted to worms of the same sex -- part of a study. Though their serpentine locomotion might be off-putting to some, when roundworms do the deed, they're surprisingly graceful. The roundworm.