Hi Greg and others
Your comments on the Golden Whistler are very interesting and may well
be a case of gender change that we are discussing.
However, may I make a couple of comments on the chromosomes, but I must
stress I'm no expert on genetics.
I agree with what Andrew Hobbs has just posted.
In birds, unlike mammals and most other vertebrates, the female is the
heterogametic sex not the male. So the male sperm are all alike and not
involved in sex determination but the ova are either "male" or "female"
depending on which sex chromosome they carry. Fertilization with a
sperm does not change this.
Also, what we are discussing here is not caused by a change in the
chromosomes, female sex chromosomes can't "change" into male chromosomes
in the one individual, but rather there are changes in the individual's
hormonal environment.
In the majority of birds (exceptions are birds of prey and kiwis) there
is a single functional left ovary. This produces various hormones
(oestrogens, androgens and progestagens) which maintain the female
organs and secondary sex characteristics. If this balance is changed
(through the loss of the functional ovary and its female hormones) then
the right, vestigial gonad develops as a male testis and produces male
hormones (androgens) leading to male secondary sexual characteristics.
The bird's chromosomes haven't changed (it is still genetically a
female) but the change in its hormone levels from the new testis can
result in changes to anatomy, physiology, behaviour and plumage. Think
of what happens to female athletes when they take androgens.
Cheers
Peter
-----Original Message-----
From:
On Behalf Of Greg
Sent: Friday, 7 July 2006 9:08 AM
To: Andrew Thelander;
Subject: Birds changing gender
Hi Andrew,
Some years ago while bird banding at Tumbi Umbi, on the Central Coast of
NSW, I retrapped an adult female Golden Whistler that was assuming male
plumage characters. I knew that it wasn't an immature male assuming
adult
plumage as the bird was very old (for a small bird) at the time and had
only
recently began assuming these characters. Its banding and retrap
history
was recorded on a specially designed card. John Disney, who was the
Curator
of Birds at the Australian Museum suggested that it was probably due to
the
deterioration of the ovaries due to age. I think that the XX (female)
chromosomes become XY (male).
So this phenomenon has been known for some time.
Regards
Greg Clancy
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