Hermaphrodite finch hints genes mould brain
Sex chromosomes split personality in bird possessing testis and ovary.
nature.com (see photo)
25 March 2003
John Whitfield
A half-male, half-female bird has added to evidence that genes - not only hormones - underlie the differences between male and female brains.
The cells on the right half of the bird's body contained male sex chromosomes, those on the left, female. The zebra finch had one testis and one ovary; its plumage was bright on its right half, and drab on its left.
It also had a split personality. When biologist Arthur Arnold of the University of California, Los Angeles, and his colleagues looked at the bird's brain, they saw that it, too, was divided into male and female sides.
The areas that control singing were bigger on the male side. Male finches court mates with loud and complex songs; females are quieter.
It had been thought that sex differences in the brain were caused by hormones released by the gonads, and were not due to the nerve cells themselves. But both halves of the brain would have received the same chemical signals from the gonads, showing that the different genetic make-up of the brain's two halves must also have had an effect.
The divided bird sang a male's song, and mated a female finch that then laid infertile eggs. The researchers put down the bird when it was almost two years old.
The bizarre zebra finch (Taeniopygia guttata) was born in a lab at Rockefeller University, New York, possibly from a cell containing both male and female chromosomes that was fertilized by two sperm.
Ornithologist John Wingfield, a member of the research team who works at the University of Washington, Seattle, was baffled when he first saw the animal - it seemed to change sex before his eyes as it turned. "It was split straight down the middle," he says.
References
1. Agate, R. J. et al. Neural, not gonadal, origin of brain sex differences in a gynandromorphic finch. Proceedings of the National Academy of Sciences, (2003).
© Nature News Service / Macmillan Magazines Ltd 2003
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