Head colours?

[AMCA26]

Give them a few Budgie mirrors.

[mattymeischke]

Tintola, a good question.
I would guess that they imprint their parents' head colour as normal/optimal. The head colours would be most often the same in wild pairs to my understanding. Perhaps this is less pronounced an effect in captivity where pairings of different head-coloured birds would be more common? The hens would be less reliably imprinted with one head colour as the parental model/optimal mate.

It seems on various lines of evidence that the different head colours are speciation in progress; cf: Niki's excerpt above ("mortality in mixed morph genotypes was particularly severe (43.6%) for the heterogametic sex (daughters), which is consistent with Haldane's rule predicted for postzygotic incompatibilities between hybridizing species"), for example.

As for why males may be preferred in resource-unreliable environments, it may be advantageous in terms of reproductive success (measured as the total number of descendants) to have more male offspring. Though less males ultimately go on to reproduce, those who do reproduce may have many more offspring per individual (over their lifetime) than hens in the same circumstances. The hen doesn't have to understand the maths, of course; it is sufficient for this trait to be propagated that there are more offspring with the trait than without it.

[maz]

Isnt it nice to be able to see some evolutionary processes occuring.....such interesting research

[mackstaa]

What determines their smuttiness TT?

Its making me remember back to my school days

AmCA Budgie mirrors, they will probably bite them demanding their 1 goildian distance in between

Did the Author of this thread get the answer he was looking for? Yeah try two pairs...at least

[mattymeischke]

If it's smutty enough, do you call it a blue gouldian? (boom, tish)

[Tintola]

In this context "Smutty" refers to the unclean colouring of the colour in the faces of the hens, on the orange and red faced Gouldians, when bred from mixed head coloured pairs. Not what they might be mumbling to each other in private.

[Niki_K]

As for why males may be preferred in resource-unreliable environments, it may be advantageous in terms of reproductive success (measured as the total number of descendants) to have more male offspring. Though less males ultimately go on to reproduce, those who do reproduce may have many more offspring per individual (over their lifetime) than hens in the same circumstances. The hen doesn't have to understand the maths, of course; it is sufficient for this trait to be propagated that there are more offspring with the trait than without it.

Precisely There is evidence that in zebra finch, female offspring from a mother in poorer condition display reduced body size and fecundity, so its in the mothers best interest to produce males, which don't appear to suffer from reduced fertility, though they may be slightly smaller.
However, this is completely opposite to many other species, where mothers in poorer condition produce daughters, as they can't 'afford' the cost of producing a large, well-coloured son. Under these circumstances, it is better to produce a daughter, as she is more likely to mate and produce offspring than a poor quality son.

[Nrg800]

mortality in mixed morph genotypes was particularly severe (43.6%) for the heterogametic sex (daughters), which is consistent with Haldane's rule predicted for postzygotic incompatibilities between hybridizing species

Just while we're at it, can anyone explain how Haldane's rule works, biologically. I understand the results and such, but why what that evolved to happen?

Edit: Like, why is mammals have males as the heterozygous sex, whereas birds have the female as the heterozygous. I understand that it's explained by Composite Theory, but I don't quite understand how that works...

[Niki_K]

mortality in mixed morph genotypes was particularly severe (43.6%) for the heterogametic sex (daughters), which is consistent with Haldane's rule predicted for postzygotic incompatibilities between hybridizing species

Just while we're at it, can anyone explain how Haldane's rule works, biologically. I understand the results and such, but why what that evolved to happen? quote]

Basically, it is a protective measure so that animals stick to their own kind, as it is in the parents best interest to find a partner that they will be able to produce viable offspring with. It is also the early stages of speciation, where animal lineages are diverging to produce offspring that are best suited to their environment.
Imagine two populations of zebra finches- a large parent population in VIC and a small population in QLD, where we assume no movement between populations. When you see changes in colour/size etc, that is the beginning of speciation (i.e. becoming a new species). Now, if you put those zebra finches together after they've been apart for 5 years, they will still be able to interbreed and produce viable offspring. But if you put the populations together after 5000 years or more, they may not be able to do so. This is because they will have evolved to the conditions peculiar to their own environment, and will have diverged accordingly. The QLD population will have some (probably a lot) of inbreeding, and unsuccessful colour morphs will have died out, either due to predation or because of mate choice. In this case, we'll say that fawn is the successful colour morph, and that they are now larger as they experience mild winters and more food available year round.
Now we catch the QLD population and put them with the VIC population. There are a number of possible outcomes in relation to hybridisation:
1.) They don't recognise each other as conspecifics and make no attempt to breed.
2.) They are able to copulate, but produce sterile hybrids of the heterogametic sex (though the homogametic sex is unaffected). This is Haldane's rule for hybrid sterility.
3.) They are able to copulate, but the heterogametic sex is absent or rare, and the homogametic sex is likely to be sterile. This is Haldane's rule for hybrid inviability.
4.) They copulate, but produce 'nothing' as embryos die before eggs are laid, or while in the egg prior to hatching, or shortly after hatching.
5.) They are unable to copulate due to physiological differences, as the "postzygotic barriers" (hybrid sterility and hybrid inviability), are replaced by "prezygotic barriers" (e.g. mating incompatibilities). This is related to 1.)

[mattymeischke]

...why ... mammals have males as the heterozygous sex, whereas birds have the female as the heterozygous.

This thread has thrown up some great questions.
The answer is: we don't know.

Firstly, to clarify, heterozygous refers to having different genes at matching spots on a pair of chromosomes. An example would be one of those 'split-blue' Gouldians, which has one gene for greenback and one for blue. All 'splits' are heterozygous for the gene in question.

Heterogametic refers specifically to the sex which has different sex chromosomes. In mammals the system for sex determination is the X and Y chromosomes. The female is homogametic, viz: her sex chromosomes are the same (XX); the male (XY) is the heterogametic sex here because his sex chromosomes are different.
In mammals, a gene on the Y chromosome (called SRY) causes testes develop, which then secrete testosterone which drives the developmental program for 'maleness'.

In birds, the sex is determined by the Z and W chromosomes, with females being ZW and males ZZ. A similar system applies in snakes. However, there is no 'femaleness' gene on the W chromosome. Sex is most likely determined by the dosage of a Z-borne gene: females only get one copy, so develop according to the 'default' program, and become females, whereas males get two copies which is sufficient to divert their development into the variation which makes males.

The heterogametic sex is predictable in mammals, birds and snakes, but even there there are exceptions.
The platypus has a chain of 10 sex chromosomes, 5 Xs and 5 Ys, some of which carry genes which correspond to genes on the avian Z. Genes which correspond to those found on the mammalian Y chromosome are found on chromosome 6 in platypus. These results suggest that the 'original' sex determination system was related to genes which are found in the avian Z chromosome, and that the mammalian XY system is an innovation in mammals which has developed since the monotreme lineage split from the mainstream mammals, from autosomal genes originally on chromosome 6.

It gets even more complicated in other animals; for example, some amphibians are capable of switching which sex is heterogametic (Stock et al, J Evol Biol 2011 May; 24(5): 1064-70.).

I understand that it's explained by Composite Theory, but I don't quite understand how that works...

I don't either, mate. The composite theory I am familiar with in evol. biol. is the composite theory of jaw development (as opposed to the serial theory). My own interpretation is that the innovation of SRY frees up the complex downstream developmental machinery of sex determination and thereby makes available many genes and gene-products for exaption to other systems in mammals. Likely exaptive puropses in humans would relate to the CNS and immune system function.

Hope this makes sense, and my apologies to readers who are less nerdy than NRG and I.