The Gouldian finch female has a neat trick for maximizing her offspring’s chance of survival: If she mates with a male who is a poor match for her genetically, she increases the proportion of male chicks in the resulting brood. In a new study, researchers say they’ve found unprecedented evidence that these birds can exert control over the gender of their offspring.
The endangered finch, native to the northern savannahs of Australia, can have either a black or red head, and the two different “morphs” have significant genetic differences, lead researcher Sarah Pryke says. “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 [Australian Broadcasting Corporation]. The birds prefer to mate with males that have the same head coloring, as chicks from a mismatched mating – particularly the females – are weaker and more likely to die very early [BBC News].
In the study, published in Science, researchers 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% male, whereas females in matched pairs produced an unbiased sex ratio with 45.9% males [Australian Broadcasting Corporation].
Then the researchers set about testing whether the females in mixed pairs were deliberately producing more sons. They tricked the females by taking red-headed males and dying their heads black. When red females mated with pseudo-black males they produced significantly more sons (72% males) despite in fact being genetically compatible. When black females mated with the pseudo-black impostors they produced similar numbers of males and females (55% males) [Cosmos].
In birds, the sex of an egg is already determined before it is fertilised by the male…. “It is pretty amazing to think that the female herself has so much control – subconsciously of course – over this basic physiology,” said Dr Pryke [BBC News]. The exact mechanism by which females determine their offspring’s sex “is a big mystery,” she said, but one possibility is that the sight of a mate with a differently coloured head raises female stress levels, producing hormones that interrupt the normal processes of fertilisation [Sydney Morning Herald].
Related Content:
DISCOVER: Sex, Ys, and Platypuses examines how gender is determined in those complicated animals
DISCOVER: A Good Reason for Sex looks at the evolution of gender
DISCOVER: The Biology of Sex Ratios wonders whether humans can unconsciously influence the sex of their offspring
Image: Sarah Pryke
March 22nd, 2009 at 11:14 am
firs comment. theees is quit intareeesting tooopik, theeenk yous for eet
March 22nd, 2009 at 8:46 pm
How do the finch mothers know what color heads they have?
March 23rd, 2009 at 9:13 am
more proof that darwinism is a sham. Individual birds generate their own adaptations (and prepare their offspring for entrance into the world) RMNS is a fairytale.
March 23rd, 2009 at 1:56 pm
@Roger: a finch mother wouldn’t need to know the colour of their own head. They’re not choosing mates on the basis of similarity to themselves. They’re choosing mates based on a genetically determined preference (black-headed females inherit a preference for black-headed males, as red-headed females do for red-headed males). If you dyed a red-headed female’s head black, it wouldn’t start preferring black-headed males.
March 23rd, 2009 at 5:35 pm
How do they know it’s ’subconscious’? Did they get the female birds to fill in a questionnaire?
March 24th, 2009 at 4:38 pm
There’s no way you just read this. It’s the paragraph that starts with “Then the researchers….”
March 24th, 2009 at 11:46 pm
Hah, that reminds me of the Bene Gesserit in Dune.
March 26th, 2009 at 5:53 pm
Hi, Roger — Jo answered your question well, I thought, but I’d already fired off a question to the researcher, Sarah Pryke, asking her to clarify. Since she was gracious enough to write back, I thought I’d share her response:
“This is a good question…. How does a grasshopper know it is a grasshopper? Or a cuckoo know it is a cuckoo (even when it is reared by another species)? Basically, females don’t know what colour they are – their preference for males of the same head colour is simply an innate genetically-determined response (i.e. hardwired) where females prefer their own type (as is seen in most species). Although they definitely use head colour to choose among different males, they are not trying to match their own head colour to their mate’s (i.e. changing their colour won’t change their mate choice as it is an inherent response). At the moment we are actually looking at the exact genetic architecture of this mate preference….”
March 29th, 2009 at 3:31 am
@ Michael: I see what you mean there; it’s almost as if they’re trying to create their OWN “Kwisatz Haderach”, or “superbeing”…..ROFLMAO!
April 3rd, 2009 at 1:24 pm
Jo and Eliza were so wrong on this. The study is a perfect sample to REFUTE sarah’s gene-determining theory.
quote: “When red females mated with pseudo-black males they produced significantly more sons (72% males) despite in fact being genetically compatible. When black females mated with the pseudo-black impostors they produced similar numbers of males and females (55% males).” – if it is “an innate genetically-determined response”, the red females would still have 50-50 chance to have sons with red males even with fake black heads.
come on, is this a joke?
April 16th, 2009 at 3:16 am
@ Bella: Did you actually read the bit you quoted?
Red female + Red male -> 46% male, 54% female
Black female + Black male -> 46% male, 54% female
Black female + pseudo-Black male -> 55% male, 45% female
Red female + pseudo-Black male -> 72% male, 28% female
Red female + Black male -> 82% male, 18% female
Black female + Red male -> 82% male, 18% female
The afore mentioned innate genetically-determined response is in regard to sexual preference, not genetic compatibility. The behaviour itself is genetically-determined (it has nothing to do with specific gene pairings in the offspring), just like bipedal locomotion, syntax driven language and the invention of deities are genetically-determined behaviours in humans.
@ Compton: Think about your sexual preferences and how you determine whether you find someone sexy… I’ll put money on it that it’s 100% subconscious, and sometimes you don’t even know why you find some people so attractive. If you can look at someone and know instantly that they’re attractive then it’s obviously not a conscious categorization. It’s assumed that most animals’ sexual selection mechanisms work in a similar fashion.
Plus, since all the birds in the study behaved in the same way, it’s highly unlikely to be a conscious process. No aspect of the behaviour even seems to be learned, indicating that it’s a genetically-determined subconscious process.
September 17th, 2009 at 4:08 pm
Doesn’t it seem that the main point of this article seems to get lost by the end? Ultimately the females’ behavior is increasing the fitness of “mixed breed” finches. Clever girls.