4 replies to this topic

[mail1234]

Hi, I'm pretty new to this aging scene but I've been reading about Rose's fly experiments and it got me thinking....feel free to criticise it

Rose's experiments in 1984 eventually showed that fecundity actually increased in flies longer living compared to control. The authors explained this via experimental problems but I disagree (as do many others). Taken at face value, the result would seem to disprove the fact that natural selection maximises fitness/reproductive activity (if they can reproduce more via simple experiments, why hasnt natural selection made them do so in the wild?).

There must be a reason that the alleles selected for in Roses experiment dont appear in the wild as frequently. The answer must be a trade off - for example, humans dont reproduce early as we need the female to be more experienced and bigger to enhance offspring survival. Drosophila lay 10s of eggs a day so something similar is unlikely to be the case.

The only thing I can think of is that the alleles that allow long living are actually deleterious in early life and beneficial in late life, the opposite of antagonisitic pleiotropy in its usual form. Any better thoughts? Im sure I'm missing something stupidly obvious but there must be a reason for the flies intermediate reproductive activity (a similar thing is seen in viruses - they evolve to become intermediately virulent because they dont want to kill the host nor do they want to spread too slowly).

Cheers

[mail1234]

No thoughts anyone?

[Hedrock]

I do not follow your conclusion.

A group of animals (a "species") is already nearly immortal. So there is no need for individual immortality.

If there would be some longer living individuals, this would be bad for the adaption of the group at all. Resources in nature are always limited (limited food, limited area). So selection is on the side of aging and death.

Under laboratory conditions food is unlimited. There are no natural enemies. So the conditions are very different.

Nature will lead selection to a shorter life. Artificial conditions like laboratories will lead to longer life.

[mail1234]

I do not follow your conclusion.

A group of animals (a "species") is already nearly immortal. So there is no need for individual immortality.

If there would be some longer living individuals, this would be bad for the adaption of the group at all. Resources in nature are always limited (limited food, limited area). So selection is on the side of aging and death.

Under laboratory conditions food is unlimited. There are no natural enemies. So the conditions are very different.

Nature will lead selection to a shorter life. Artificial conditions like laboratories will lead to longer life.

Ok I understand that and agree, but I quote:

"A great deal of this mathematical science derives from the premise that natural selection optimizes life histories for reproductive potential, which is a weighted integral of fertility over an individual lifetime. If this quantity is under strong directional selection in nature, it should be very difficult to increase it further by laboratory selection." Mitteldorf (2004) 'Ageing selected for its own sake'

Does this not make sense? If reproductive ability is one of the most strongly selected characteristics then why is it so easy to increase this ability artificially? Would you say it's simply that resources in the wild are not as plentiful? That would make sense I guess...

And even so, do you think that genes which are deleterious in early life but beneficial in late life could be selected for in these experiments just as much as genes that are deleterious in late life are selected against? It makes sense to me that they could but Im struggling to find anything written about this (which probably means I'm an idiot ). Of course it would probably take longer as you have to wait for the right mutation/allele to appear which would take a while. This could also explain the reduced early fecundity maybe? (deleterious early on).

Anyway, I accept that I'm probably wrong but it was just an idea I had

Edited by mail1234, 24 April 2010 - 03:16 PM.

[Hedrock]

Anyway, I accept that I'm probably wrong but it was just an idea I had

No, no! This subject is too interesting.Let's discuss it controversially.

I just answered to your scattered thoughts with my own scattered thoughts. What I say is probably not the ultimate answer!

Does this not make sense? If reproductive ability is one of the most strongly selected characteristics then why is it so easy to increase this ability artificially? Would you say it's simply that resources in the wild are not as plentiful? That would make sense I guess...

Is it easy to increase reproductive ability? I don't know if this is general true.

In the industrial nations men nearly live under "laboratory conditions". No contact to nature necessary. Enough food and no natural enemies. The life span is raising, yes!

But we can not reproduce any more. The birth rates are sinking every year. At the moment in our country the birth rate is at 1,3 children per woman.Tendency sinking.

Different from this in the third world countries we have still a high birth rate. But why? Any explanation? I would expect high birth rates rather under good conditions than under bad conditions.

So if it is so easy to increase reproduction: My gouvernment would be grateful for a solution. How could we increase reproduction in industrial nations?

And even so, do you think that genes which are deleterious in early life but beneficial in late life could be selected for in these experiments just as much as genes that are deleterious in late life are selected against? It makes sense to me that they could but Im struggling to find anything written about this (which probably means I'm an idiot ). Of course it would probably take longer as you have to wait for the right mutation/allele to appear which would take a while. This could also explain the reduced early fecundity maybe? (deleterious early on).

I generally would agree to the hypothesis but it is not universal.

Well, the antagonistic pleiotropy hypothesis gives us an example:

The good/bad testosterone hypothesis.

An example of this is testosterone levels in male humans. Higher levels of this hormone lead to increased fitness in early life, while causing decreased fitness in later life due to a higher risk for prostate cancer.[11] This is an example of antagonistic pleiotropy being an explanation for senescence. Senescence is the act of ageing in individuals; it's the failure over time of the individual's life processes by natural causes.

Example taken from wiki

I don't know if this example is a good example. We can not say that testosterone is generally bad in aged individuals. There are some "side effects" like prostate cancer which limit lifespan. But according to scientific research I can not see a general problem with testosterone. Maybe DHT (dihydrotestosterone) would be a problem, but there are other ways to control ist. There are other solutions for the prostate problem than stopping the testosterone. Testosterone is important for aged persons.

I would rather say that the sinking DHEA level and the sinking melatonin level could be a problem leading to a DHEA/testosterone imbalace?

Am I going to much into details?

General hypothesis are easy made but the devil is in the detail.

Edited by Hedrock, 25 April 2010 - 09:17 AM.