Aussie Finch Forum

Someone once said . .

For every complex question, there is a simple answer . .





and it is invariably wrong

I'll stick to my guns

If you read the abstract which GregH provided a link to, you can see that some work has been done in this area on pigeons.
I can not get access to the full article, but I am sure it will tell you the proportion of male and female chicks from the first egg.
While "hormones" play a part , I suspect that we do not have the knowledge to explain how these chemicals produce the results they do.
As for speed of action, if you think of adrenaline as a hormone, which works within seconds and the effects fade minutes after the levels fall, they do have the capacity to turn on and off very quickly.

Cheers
Brett

G'day Brett, I read the abstract, and it doesn't provide the information to answer some of my questions, hence why I have asked. Unfortunately I have changed jobs and can no longer get full articles. Yes adrenaline springs to mind as do many others. However there must be a very specific mechanisms to switch on/off the hormone so that it can change the gametes and bring forward successive yet distinctly separate male and female ovulations within 2 days to bring about one of each egg.
The mystery goes on and Arthur I do believe in Occam's razor.

If the answer were simple the owners of chicken hatcheries would be using it already to reduce costs as there is a lot of money tied up with this answer given the size of the poultry industry and hatred of the animal rights lobby to the post-hatching cockerel cull.

Sorry you couldn't get to the primary article but I can point you to an alternative source from the authors Vivian C. Goerlich Ton G. G. Groothuis; a book chapter Are maternal hormones involved in the manipulation of avian primary offspring sex ratio?. It's tough going and does specifically address the dilemma that the "sex" of the ovum is set well before the maturation starts so how does it choose which follicle to mature. In an earlier paper by Correa, S.M.; Adkins-Regan, E.; Johnson, P.A. (2004) (High progesterone during avian meiosis biases sex ratios toward females. Biology Letters doi: 10.1098/rsbl.2004.0283), they show that in chickens an artificial pulse of progesterone injected 6h prior to ovulation did bias the primary sex ratio towards females (controls & low progesterone gave ~35% female and high dose gave rise to 75% female) but as Goerlich points out it's not that simple. Manipulation of the primary sex ratio of the eggs laid occurs without gaps so the selection of the follicles destined for a clutch occurs prior to maturation rather than on a daily basis as the follicles mature. You may get more from it than I can but I've got other jobs to attend to so I'll have to leave it there.

Greg

The pigeon pair principle certainly didn't hold true with the red-bellied spinifex pigeons. A mate had four rounds of two chicks. All were DNA sexed and the results came back as pairs.

I was next on the list to get a pair (round number 5), and decided that there would be no need to get them DNA sexed. Well one year wasted because both turned out to be cocks.

Tossing a coin is about as close as you will get to a TRUE even-money chance

When tossing 2 coins (or 1 coin twice) the chance of tossing a head and a tail is an even-money chance . .

BUT . . when tossing 4 coins (or 1 coin 4 times) the chance of 2 heads and 2 tails is much less than even-money

And when tossing 1 000 coins, the chance of 500 heads and 500 tails is extremely unlikely

Now replace the word 'coin' with 'egg' . . the word 'head' with 'cock' . . the word 'tail' with 'hen'

Even if there is some kind of bias (which could be called a complex nuance) that causes pigeons to 'tend toward' equilibrium . . the chances of actual equilibrium over even a smallish number of clutches is low; and of equilibrium over large numbers of clutches is extremely remote indeed

Thus the 'pigeon-pair' proposition is . . an URBAN MYTH

Edited once for the sake of 'good science'

And I would be more than happy to put my money where my mouth is

Thanks Greg, appreciate the information, like all things in biology if it was that simple we would be using it to our commercial advantage more then we do now.

Arthur you crack me up , comparing two coins where the chance of tossing a head or tail is approximately equal cannot be used to simplistically compare the complex nuances of how birds manipulate their sex ratios Keep up the good work.

I believe that - given a normal hormone balance (whatever that is!) - pigeon species that lay 2 eggs seem to produce a balance of sexes (ie Pigeon Pair).
The article referred to earlier (and I can't see the whole thing either) suggests that you can change the sex ratio by altering the sex hormones in the hen. That seems quite reasonable. Sexual selection is well known in every stage of the reproductive process in the animal world.

I seem to remember something about Gouldians on this topic (hormonal influence on offspring) somewhere.

The sex selection work was done by Sarah Pryke in Blue-Face Parrot Finches and the Gouldian work will have to wait until I can get back to this computer..

Trilobite on 04 May 2011, 11:52 . . On Bleeding Hearts

I purchased a pair last year from a produce agency who were selling them absurdly cheap ( wont say how much) as they must have just been recently fledged and weaned - head feathers were moulting and the colours very washed out. Thankfully theny survived but as yet have never done anything until I had them DNA sexed (a must) and found that they wouldnt do too much as they were both females

Hope they weren't nestmates . .

That would upset some theorists