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guslfrom Wikipedia: Liger
This is very unsatisfactory! Since it's lacking references, I am including it here as an instance of psychoceramics. It exemplifies a common sort of confusion.
His argument basically says that male lions are predisposed to have large children, and female lions to have small children. The problem is that the article tries to explain this difference by talking about 100% Lion prides, in which these children are the same: each cub will be the child of exactly one male lion and one female lion! At each breeding instance (disregarding opportunity costs), the Darwinian score of the father due to this child is exactly the same as the Darwinian score of the mother due to this child. So if anything, natural selection should make them work in unison!
One could read the article as suggesting that the Darwinian score of male cubs would gain from a marginal increase in size, while female cubs would gain from a marginal decrease in size. This seems plausible, but this would be plain sexual dimorphism, and there's no reason why one parent should contribute more to it than the other.
Anyway, a related idea:
If X chromosomes promote smallness and Y promotes largeness,
then a lion's X + a tiger's X should make a female Liger whose size is between that is tiger and lion females.
It is believed that this is because female lions transmit a growth-inhibiting gene to their descendants to balance the growth-promoting gene transmitted by male lions. (This gene is due to competitive mating strategies in lions.) A male lion needs to be large to successfully defend the pride from other roaming male lions and pass on his genes; also, in prides with multiple male adult lions, a male's cubs need to be bigger than the competing males for the best chance of survival. Thus, his genes favor larger offspring. A lioness, however, will have up to 5 cubs, and a cub is typically one of many being cared for in a pride with many other lions. As such, it has a relatively high survival rate, and need not be huge as it will not need to look after itself very quickly. Smaller cubs are more easily cared for and fed and are less strain on the pride; hence, the inhibiting gene developed.
This is very unsatisfactory! Since it's lacking references, I am including it here as an instance of psychoceramics. It exemplifies a common sort of confusion.
His argument basically says that male lions are predisposed to have large children, and female lions to have small children. The problem is that the article tries to explain this difference by talking about 100% Lion prides, in which these children are the same: each cub will be the child of exactly one male lion and one female lion! At each breeding instance (disregarding opportunity costs), the Darwinian score of the father due to this child is exactly the same as the Darwinian score of the mother due to this child. So if anything, natural selection should make them work in unison!
One could read the article as suggesting that the Darwinian score of male cubs would gain from a marginal increase in size, while female cubs would gain from a marginal decrease in size. This seems plausible, but this would be plain sexual dimorphism, and there's no reason why one parent should contribute more to it than the other.
Anyway, a related idea:
If X chromosomes promote smallness and Y promotes largeness,
then a lion's X + a tiger's X should make a female Liger whose size is between that is tiger and lion females.
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(no subject)
Date: 2006-05-21 10:13 pm (UTC)As adults, the measure of male success is success as an individual while the measure of female success is success as a member of a pride. Larger males are successful because they can defend their pride against danger. Smaller females are successful because they do not require a lot of the resources of the pride. For example, a smaller female may need less food and may be better at hiding than her larger counterpart. It would make sense if growth in lions became sex related such as XX, female chromosomes, promoted smallness, and XY promoted largeness. So while there may be a female gene that may trigger smallness, it could perhaps be a recessive gene that is only triggered when the two X chromosomes are present. While there may a male gene that promotes largeness, it may be tempered by the female gene that promotes smallness.
Adult tigers are mostly solitary so being small is not particularly useful for a female tiger. The lack of that tempering in the ligers can make them bigger than both the lions and the tigers.
So how is that for an explanation that I completely made up?
(no subject)
Date: 2006-05-22 12:04 am (UTC)But what about male Ligers? Are they then huge for the same reason as the female Ligers, namely because they miss the "smallening" Lion X?
If this is correct, it's interesting how work the Lions' genes work against each other: it seems unnecessary to have both a "biggening" Y a "smallening" X, since any one of them should be enough.
Against this theory, though, seems to be the observation that Tigons are not significantly smaller than their parents. (or am I wrong?)
(no subject)
Date: 2006-05-22 12:15 am (UTC)(no subject)
Date: 2006-05-22 01:00 am (UTC)(no subject)
Date: 2006-05-22 01:07 am (UTC)Can you make this more precise?
AFAICT, the only difference are the future opportunity costs, which tend to be much greater for the mother (because she sacrifices future breeding opportunities). The success of a child affects both parents' Darwinian scores equally.
(no subject)
Date: 2006-05-22 02:38 am (UTC)(no subject)
Date: 2006-05-22 03:17 pm (UTC)All evolutionary fitness in measured in ONE WAY: how many times does an individual manage to produce offspring that are going to produce offspring as well: to make good offspring (over the course of a life time) you can either *invest* a lot per individual or have a lot of offspring...
There are big disparities between male and female investment in a single offspring though...
Females invest more resources in an offspring than males do. This is true in many (but not all) species, including (btw) humans. It begins with the egg. This is a big investment and a female has a limited supply, it proceeds with the investment into the organism during development which saps the mothers strength while the father is off cavorting (often not provisioning and providing, particularly not in Lion prides) and *importantly* he is having more offspring while all the female's resources are completely invested in one developing offspring. Small offspring sap less of your resources.
Part of the problem for females is that this mate talked a pretty good game pre-copulation (showed off, or whatever) but did he have quality genes or is this offspring going to be pretty useless? This mystery is where male bravado and showy manes come from... If you can maintain a big stupid tuft of mane then maybe your genes are OK. Maybe that is just a lie though. Mate choice is tough. A female doesn't want to invest too much in this offspring, to save her strength and have more later she silences genes that tend to make the offspring gigantic.
As to the mechanisms of competing genes (or gene silencing/imprinting mechanisms) I doubt that the mechanisms or genes for Lions are known. We don't have the tools to study them. This sort of sexual competition is being studied these days in Mice or Flies and the findings are thought to possibly be extended to other organisms. I am no expert so you could try reading more about it other places:
Google -scholar- for:
Genomic imprinting in mammalian development: a parental tug-of-war.
See yah!
hh
(no subject)
Date: 2006-05-22 03:59 pm (UTC)Exactly. What I call "Darwinian score" is exactly this recursive notion.
Do females ever run out of eggs?
Right. This "handicap" idea and sexual selection in general seems to make our world a lot more interesting: deer antlers, peacock tails, music, etc. High testosterone levels are also a handicap, since it weakens the immune system.
Are you suggesting that a mother can choose in which kids to silence those genes?
My point is that the Darwinian score of a mother will be the same as that of her partners. This is obviously true if we assume monogamy. Now, this is still the case if we add a couple to swing with them. By induction, all mating configurations can be found. Oops, scrap that! :-)
ok, I can now see the tug-of-war (escalation):
The more successful males are those who make their kids as big as possible, whereas the females who make many smaller kids may end up being more successful. But this would mean that size is not as important it may have seemed: the mothers "benefits" from each large kid just as much as the father. If we assume that female with smaller kids will breed twice as much (a generous assumption, no?), this means that the average big kid will score less than twice as much as his normal-sized counterpart.
The dynamics of this can be quite complex and confusing, but it's still interesting to see how far we can take our qualitative arguments.
(Btw, in Dutch and German, your initials are pronounced "haha".)
(no subject)
Date: 2007-02-27 09:54 pm (UTC)(no subject)
Date: 2008-03-26 12:26 pm (UTC)(no subject)
Date: 2008-03-26 01:37 pm (UTC)