I thought this might be of general interest
http://www.abc.net.au/news/stories/2009/03/20/2521613.htm
Finch head colour affects sex of chicks
By Science Online's Dani Cooper
Female finches from northern Australia are controlling the sex of their
offspring, according to the head colour of their male counterpart.
The finding, published today in the journal Science, is one of the first to
clearly show that birds are capable of biasing the sex of their offspring to
overcome genetic weaknesses.
Lead author Dr Sarah Pryke, from the department of brain behaviour and
evolution at Macquarie University in Sydney, admits the mechanism by which
the birds do this is not yet known.
The endangered Gouldian finch (Erythrura gouldiae), which is found in the
northern savannahs of Australia, can have either black or red heads.
Dr Pryke says some genetic incompatibility between the black and red-headed
birds results in high mortality in the offspring when birds of different
head colours mate.
With female offspring this mortality rate can be as much as 80 per cent
higher than in a same-head colour pairing. Sons in a mixed pairing have a 40
per cent mortality rate.
Dr Pryke found that if the female mates with a finch of different head
colour, she attempts to overcome this genetic incompatability by
over-producing sons - as much as four males to one female.
"This is the first time such a large effect has been shown," says Dr Pryke.
"It is actually the female that is controlling the gender."
Changing colour
To reach this conclusion Pryke and colleague Simon Griffith took 100
red-headed and 100 black-headed female birds and mated them with a male of
the same head colour and a male with the different head colour.
They found females in mixed pairs produced broods that were 82.1 per cent
male, whereas females in matched pairs produced an unbiased sex ratio with
45.9 per cent males.
They then tested whether the females in mixed pairs were deliberately
over-producing sons.
Female birds were tricked into thinking they were mating with an
incompatible male.
The researchers did this by temporarily blackening the head colour of red
males and mating them with red and black-headed females.
The black females paired to red males with blackened heads produced a sex
ratio that was roughly equal.
By contrast red females paired with red males that had blackened heads
over-produced sons at a ratio similar to a mixed pairing.
Wearing their genes
Dr Pryke says there is no chemical or genetic interaction between the
parents at work.
"Gouldian finches wear their genes on their head so it is easy for a female
to assess the genetic suitability of the male," she says.
"Change the colour of the male's head with dye and the sex ratio changes."
Through the study the researchers also found that females from mixed pairs
produced fewer and smaller eggs.
Dr Pryke says the finding is important because up to 30 per cent of breeding
pairs in the wild are mixed "perhaps because of constraints on preferred
mate availability".
Professor Ben Sheldon, director of the University of Oxford's Edward Grey
institute of field ornithology, says the results demonstrate "hitherto
unsuspected degrees of control over reproductive investment by female
birds".
"This work opens new possibilities in unravelling the mechanisms behind
these striking behaviours, something which has up to now remained an
unsolved mystery," he says.
-Read more science stories at ABC Science Online.
Tags: science-and-technology, animals, birds, australia, nt, qld, wa
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