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Animals with a built-in self-destruct mechanism - Comments

Deako's Avatar Comment 1 by Deako

Don't know - but there's no source for this info in the Wikipedia article...

Greg

Mon, 21 Nov 2011 14:15:30 UTC | #891994

Peter Grant's Avatar Comment 2 by Peter Grant

It's not that there is selective pressure for a "genetically programmed death", it's that there is little or no selective pressure to stop such a harmful mutation from spreading through a population because most individuals would have starved shorty after reproducing anyway.

Mon, 21 Nov 2011 14:40:13 UTC | #892003

Red Dog's Avatar Comment 3 by Red Dog

Comment 2 by Peter Grant :

It's not that there is selective pressure for a "genetically programmed death", it's that there is little or no selective pressure to stop such a harmful mutation from spreading through a population because most individuals would have starved shorty after reproducing anyway.

But the octopuses that don't have the genetic defect can procreate several times and hence have many more offspring. So without some additional factor it is a mystery to me (assuming the Wikipedia article is even correct as Greg points out in comment 1)

Something that might explain it would be if the Octopus is only fertile for a short amount of time so unlikely to be able to procreate more than once anyway. In that case I could see how the mutation could actually be beneficial as there is no genetic reason to keep infertile octopuses around -- competing for the same food sources as fertile ones.

Mon, 21 Nov 2011 15:14:01 UTC | #892013

Peter Grant's Avatar Comment 4 by Peter Grant

If you are going to compare genes to a computer program then it's better to think of death as a system crash. When a program "dies" or stops working properly we generally call it a bug. Death is not a feature.

Mon, 21 Nov 2011 16:02:39 UTC | #892021

Michael Austin's Avatar Comment 5 by Michael Austin

If the octopus doesn't protect its young, and doesn't reproduce more than once, it is of no value to its selfish genes. The genetically programmed death could leave more room for its offspring to find a home without having to compete with their parents. Notice that octopuses have a lot of young, so the territory that she would need to survive would be of more benefit to her offspring(as long as it helps 3 or more), and the cell-death is evolutionarily advantageous. I could be wrong, but it logically makes sense.

Mon, 21 Nov 2011 16:13:36 UTC | #892024

Red Dog's Avatar Comment 6 by Red Dog

Comment 4 by Peter Grant :

If you are going to compare genes to a computer program then it's better to think of death as a system crash. When a program "dies" or stops working properly we generally call it a bug. Death is not a feature.

I don't understand how that relates to this discussion but I disagree with your analogy. In fact its very important for a program to be well designed so that when you want to end it, it can do so properly. For example, not leave bits of memory or files so that the OS thinks they are still in use when they aren't.

Mon, 21 Nov 2011 16:13:44 UTC | #892025

DaveUK9xx's Avatar Comment 7 by DaveUK9xx

This behaviour is similar to that of salmon or eels both of which die after spawning. For species that produce many offspring and are not required to be around to provide parental care it may be an advantage for the adults to die so as not to compete with the young for food or territory. For more advanced animals such as mammals which do need to provide parental care and can only produce small litters then a longer lifespan and multiple litters is a better strategy.

Mon, 21 Nov 2011 16:16:04 UTC | #892027

Stephen of Wimbledon's Avatar Comment 8 by Stephen of Wimbledon

I cannot claim to be an expert...

That said, some possible reasons are:

  1. An early, relatively isolated, population of these octopi evolved the trait of not eating in order to allow food supplies to increase while the eggs develop.

  2. However, if there were any cheaters in 1 they would have had more offspring and the altruistic octopi would die out.

  3. If the isolated population simply evolved a death clock (of the type seen here) then there can be no cheaters - so the species survives with this trait. Such a thing is perfectly possible. Just because it seems barmy doesn't mean that having a death clock wasn't an evolutionary advantage at some point.

If both 1 & 3 are correct then this particular species of octopi would have had an advantage over other octopi (or any species that competes for its resources) - providing they too had no cheaters. By dying on schedule the parents give all offspring in their species both the best chance, and a fairer chance, of survival - thus better guaranteeing the future direct survival through better access to food (etc.) and their future indirect survival through enhanced genetic variability.

The above is all based on a theory of evolution called the evolutionarily stable strategy (ESS). I recommend you look this up, it is very interesting when you get into it.

  1. It is very hard to think of a way in which a death clock would be partly useful. However, part of a death clock is much easier. This particular species may, for example, have started out by evolving a hibernation, or stasis, allele. This is a halfway house between staying alive, just kicking around, to see the eggs hatch - and simply switching off.

There would probably have been some pressure on the hibernating / paralysed octopi to move them to reproduce using longer and longer clocks - until simply dying became viable.

  1. Perhaps a migrating octopi-eating predator used to happen by at a similar time to egg-laying. Those who woke too early were simply eaten - leaving those with the longest hibernation clocks to pass on longer and longer lasting clocks to their young.

  2. More likely; The death clock gene is somehow associated with some other allele. So switching on a death clock (or a longer hibernation clock) also gave better egg-hiding instincts (perhaps a longer clock related to better hiding techniques for both egg and parent?).

Or, perhaps, hibernation clock gene also made eggs more and more poisonous to a predator (now extinct because they failed to adapt?). Or perhaps that predator is still around but evolved the instinct to avoid the eggs of this particular species of Octopus?

Or a mixture of 2 and 3?

It is often misunderstood that a gene = a trait. It is not as simple as that.

It seems to me that there are many more interesting possibilities.

Mon, 21 Nov 2011 16:19:13 UTC | #892028

Stephen of Wimbledon's Avatar Comment 9 by Stephen of Wimbledon

The paragraph numbering system is screwed on RD.net, sorry.

It should read: Or a mixture of 1 & 1 - meaning the last two numbered paragraphs.

Mon, 21 Nov 2011 16:23:53 UTC | #892030

Peter Grant's Avatar Comment 10 by Peter Grant

Death is like a blue screen, when the entire OS freezes. If you don't get my analogy then it is because you are thinking in terms of group selection. Selfish genes are selfish, they don't give a damn about the group. Organisms die of old age because they are only built well enough to get by long enough to copy their selfish genes.

Comment 6 by Red Dog

I don't understand how that relates to this discussion but I disagree with your analogy. In fact its very important for a program to be well designed so that when you want to end it, it can do so properly. For example, not leave bits of memory or files so that the OS thinks they are still in use when they aren't.

Mon, 21 Nov 2011 16:24:15 UTC | #892031

Red Dog's Avatar Comment 11 by Red Dog

Comment 10 by Peter Grant :

Death is like a blue screen, when the entire OS freezes. If you don't get my analogy then it is because you are thinking in terms of group selection. Selfish genes are selfish, they don't give a damn about the group. Organisms die of old age because they are only built well enough to get by long enough to copy their selfish genes.

Selfish genes don't care about living they care about reproducing. As Stephen of Wimbledon points out above, if an animal doesn't need to take care of its young and is unlikely or incapable of further procreation death can be a feature not a bug. From the standpoint of the genes the survival of the parent no longer matters its the survival of the offspring. So if the parent can't make more offspring, isn't helping the offspring it has and is competing with those offspring for resources death makes perfect sense from the standpoint of the selfish genes.

Mon, 21 Nov 2011 16:41:43 UTC | #892033

Schrodinger's Cat's Avatar Comment 12 by Schrodinger's Cat

Arguments about competing for resources would only make sense if a mother could consume more than half of all the resources her offspring could.

For example.......mother has 100 offspring...

1) If mother dies right away.....all 100 offspring get a chance to survive

2) If mother lives on but consumes 60% of the resources........only 40 offspring get a chance to survive, which means that even if she reproduced again there would still only be 80 offspring able to survive...so it would make sense for the mother to die after producing the first offspring.

3) If mother survives but consumes 40% of the resources.......that leaves 60 offpsring with a chance to survive. Which means if she reproduced again there would be 120 offspring........so reproducing again would be favoured.

OK that's a litle basic....but you get the gist.

I would imagine that resources would have to be pretty scarce if a single octopus could eat half of all the food necessary to support the offspring.

Mon, 21 Nov 2011 18:09:31 UTC | #892055

Stephen of Wimbledon's Avatar Comment 13 by Stephen of Wimbledon

In response to Comment 12.

Hi Pussy Cat,

I wasn't making an argument, just trying out a few basic hypotheses.

Your model, incidentally, appears to be based on constants where (surely?) variables exist.

Variables large enough to affect the result are possibly innumerable, but are likely to include:

  • Variables that affect parent's ability to support eggs (e.g. lifespan)

  • Variables that affect food supply (e.g. water temperature)

  • Variables that affect shelter availability (e.g. competing species)

  • Variables that affect egg survival to hatching (e.g. predation)

  • Variables that affect hatchling survival to adulthood (predation, disease, ...)

  • Weather

  • The early death of parents might affect any number of variables relating to the survival of offspring. I can think of situations where all the above might be enhanced - or just as importantly mitigated - by a parent's early death (except maybe weather).

    Peace.

  • Mon, 21 Nov 2011 18:35:54 UTC | #892062

    Schrodinger's Cat's Avatar Comment 14 by Schrodinger's Cat

    Comment 13 by Stephen of Wimbledon

    Your model, incidentally, appears to be based on constants where (surely?) variables exist.

    The issue is not so much the variables, but whether those variables affect the mother and offspring equally. One could turn your latter variables round the other way and argue that issues that too adversely affect the offspring survival would make the survival of the mother......to produce more offspring.....more important.

    There's a fascinating program called Darwinbots.....

    http://wiki.darwinbots.com/w/Main_Page

    ......which has a huge number of tweekable parameters for which one might be able to replicate what is going on with this species.

    Mon, 21 Nov 2011 19:44:05 UTC | #892084

    Peter Grant's Avatar Comment 15 by Peter Grant

    Here's the bit from The Selfish Gene where Prof Dawkins explains ageing without having to resort to any kind of group selection nonsense:

    The question of why we die of old age is a complex one, and the details are beyond the scope of this book. In addition to particular reasons, some more general ones have been proposed. For example, one theory is that senility represents an accumulation of deleterious copying errors and other kinds of gene damage which occur during the individual's lifetime. Another theory, due to Sir Peter Medawar, is a good example of evolutionary thinking in terms of gene selection.* Medawar first dismisses traditional arguments such as: 'Old individuals die as an act of altruism to the rest of the species, because if they stayed around when they were too decrepit to reproduce, they would clutter up the world to no good purpose.' As Medawar points out, this is a circular argument, assuming what it sets out to prove, namely that old animals are too decrepit to reproduce. It is also a naive group-selection or species-selection kind of explanation, although that part of it could be rephrased more respectably. Medawar's own theory has a beautiful logic. We can build up to it as follows.

    We have already asked what are the most general attributes of a 'good' gene, and we decided that 'selfishness' was one of them. But another general quality that successful genes will have is a tendency to postpone the death of their survival machines at least until after reproduction. No doubt some of your cousins and great-uncles died in childhood, but not a single one of your ancestors did. Ancestors just don't die young!

    A gene that makes it possessors die is called a lethal gene. A semi-lethal gene has some debilitating effect, such that it makes death from other causes more probable. Any gene exerts its maximum effect on bodies at some particular stage of life, and lethals and semi¬ lethals are not exceptions. Most genes exert their influence during foetal life, others during childhood, other during young adulthood, others in middle age, and yet others in old age. (Reflect that a caterpillar and the butterfly it turns into have exactly the same set of genes.) Obviously lethal genes will tend to be removed from the gene pool. But equally obviously a late-acting lethal will be more stable in the gene pool than an early-acting lethal. A gene that is lethal in an older body may still be successful in the gene pool, provided its lethal effect does not show itself until after the body has had time to do at least some reproducing. For instance, a gene that made old bodies develop cancer could be passed on to numerous offspring because the individuals would reproduce before they got cancer. On the other hand, a gene that made young adult bodies develop cancer would not be passed on to very many offspring, and a gene that made young children develop fatal cancer would not be passed on to any offspring at all. According to this theory then, senile decay is simply a by-product of the accumulation in the gene pool of late-acting lethal and semi-lethal genes, which have been allowed to slip through the net of natural selection simply because they are late-acting.

    The aspect that Medawar himself emphasizes is that selection will favour genes that have the effect of postponing the operation of other, lethal genes, and it will also favour genes that have the effect of hastening the effect of good genes. It may be that a great deal of evolution consists of genetically-controlled changes in the time of onset of gene activity.

    It is important to notice that this theory does not need to make any prior assumptions about reproduction occurring only at certain ages. Taking as a starting assumption that all individuals were equally likely to have a child at any age, the Medawar theory would quickly predict the accumulation in the gene pool of late-acting deleterious genes, and the tendency to reproduce less in old age would follow as a secondary consequence.

    As an aside, one of the good features of this theory is that it leads us to some rather interesting speculations. For instance it follows from it that if we wanted to increase the human life span, there are two general ways in which we could do it. Firstly, we could ban reproduction before a certain age, say forty. After some centuries of this the minimum age limit would be raised to fifty, and so on. It is conceivable that human longevity could be pushed up to several centuries by this means. I cannot imagine that anyone would seriously want to institute such a policy.

    Secondly we could try to 'fool' genes into thinking that the body they are sitting in is younger than it really is. In practice this would mean identifying changes in the internal chemical environment of a body that take place during ageing. Any of these could be the 'cues' that 'turn on' late-acting lethal genes. By simulating the superficial chemical properties of a young body it might be possible to prevent the turning on of late-acting deleterious genes. The interesting point is that chemical signals of old age need not in any normal sense be deleterious in themselves. For instance, suppose that it incidentally happens to be a fact that a substance S is more concentrated in the bodies of old individuals than of young individuals. S in itself might be quite harmless, perhaps some substance in the food which accumulates in the body over time. But automatically, any gene that just happened to exert a deleterious effect in the presence of S, but which otherwise had a good effect, would be positively selected in the gene pool, and would in effect be a gene 'for' dying of old age. The cure would simply be to remove S from the body.

    What is revolutionary about this idea is that S itself is only a 'label' for old age. Any doctor who noticed that high concentrations of S tended to lead to death, would probably think of S as a kind of poison, and would rack his brains to find a direct causal link between S and bodily malfunctioning. But in the case of our hypothetical example, he might be wasting his time!

    There might also be a substance Y, a 'label' for youth in the sense that it was more concentrated in young bodies than in old ones. Once again, genes might be selected that would have good effects in the presence of Y, but which would be deleterious in its absence. Without having any way of knowing what S or Y are—there could be many such substances—we can simply make the general prediction that the more you can simulate or mimic the properties of a young body in an old one, however superficial these properties may seem, the longer should that old body live.

    I must emphasize that these are just speculations based on the Medawar theory. Although there is a sense in which the Medawar theory logically must have some truth in it, this does not mean necessarily that it is the right explanation for any given practical example of senile decay. What matters for present purposes is that the gene-selection view of evolution has no difficulty in accounting for the tendency of individuals to die when they get old. The assumption of individual mortality, which lay at the heart of our argument in this chapter, is justifiable within the framework of the theory.

    Mon, 21 Nov 2011 20:34:59 UTC | #892097

    DavidXanaos's Avatar Comment 16 by DavidXanaos

    well,

    according to the Wiki article Octopuses, if the glands are removed live until they die form starvation, so there is no competition for food with the offspring.

    all other examples I know of animals that die after giving birth is that they die of fatigue or starvation, but not by triggering a gland to turn the body off.

    David X.

    Mon, 21 Nov 2011 21:31:14 UTC | #892110

    PatW's Avatar Comment 17 by PatW

    The OP citation from Wiki is a prime example why I have a deep aversion to depending on anything from Wiki. I much prefer credible academic sources such as National Geographic:

    http://animals.nationalgeographic.com/animals/invertebrates/common-octopus/

    It just could be that nature knows best on genomes and longevity. Perhaps, the short life span of octopodes is nature's way of avoiding overpopulation of the carnivorous octopus.

    Mon, 21 Nov 2011 22:03:37 UTC | #892120

    PatW's Avatar Comment 18 by PatW

    Does anyone know where "selfish genes" are located on genomes?

    Mon, 21 Nov 2011 22:21:25 UTC | #892123

    Alan4discussion's Avatar Comment 19 by Alan4discussion

    Certainly in the case of some, vast numbers of eggs are produced, guarded and cared for over an extended period, starving and exhausting the mother in the process.

    The giant octopus lives 3-5 years. When sexually mature, females lay eggs on the inner side of a rocky den and may lay 20,000 to 100,000 eggs over a period of several days. Eggs are tended, cleaned and aerated by females until they hatch. Incubation takes 150 days to 7 or more months, depending on the temperature. Females do not feed while tending eggs and die when the eggs hatch or shortly thereafter. Many of the eggs will die if not tended by the female until hatching. - http://marinebio.org/species.asp?id=60

    I think the sheer number of eggs and offspring compensates for only breeding once.

    from the Wiki article:-

    After they have been fertilized, the female lays about 200,000 eggs (this figure dramatically varies between families, genera, species and also individuals). The female hangs these eggs in strings from the ceiling of her lair, or individually attaches them to the substrate depending on the species. The female cares for the eggs, guarding them against predators, and gently blowing currents of water over them so that they get enough oxygen. The female does not hunt during the roughly one-month period spent taking care of the unhatched eggs and may ingest some of her own arms for sustenance. At around the time the eggs hatch, the mother leaves the lair and is too weak to defend herself from predators like cod, often succumbing to their attacks.

    It varies from species to species, but clearly the females burn themselves out caring for the eggs until they hatch, and surviving males would probably be competing with the young, and could well be eating them.

    While most octopuses are cannibalistic, O. mercatoris is less cannibalistic than other species, and is sometimes found in small groups under rocks.. For fish keeping enthusiasts - It is assumed, and quite logically so, that an octopus will eat any companion fish in the aquarium.

    Selection could well favour a massive one off reproduction, especially if any other bodily organs deteriorated rapidly with age. From the numbers there are clearly massive mortality rates for the young hatchlings.

    Mon, 21 Nov 2011 22:31:20 UTC | #892127

    Red Dog's Avatar Comment 20 by Red Dog

    Comment 18 by PatW :

    Does anyone know where "selfish genes" are located on genomes?

    Was that meant to be a joke?

    Mon, 21 Nov 2011 23:55:33 UTC | #892149

    Red Dog's Avatar Comment 21 by Red Dog

    Comment 19 by Alan4discussion :

    Certainly in the case of some, vast numbers of eggs are produced, guarded and cared for over an extended period, starving and exhausting the mother in the process....

    Excellent info. So that makes sense. If the females burn themselves out after one massive procreation death after could definitely make sense. Not just to prevent them from taking resources from the offspring but also to prevent males from wasting their energy trying to impregnate a female who couldn't pull off the same amazing procreation twice.

    Tue, 22 Nov 2011 00:01:15 UTC | #892150

    Stephen of Wimbledon's Avatar Comment 22 by Stephen of Wimbledon

    In response to Comment 14 by Schrodinger's Cat

    The issue is not so much the variables, but whether those variables affect the mother and offspring equally. One could turn your latter variables round the other way and argue that issues that too adversely affect the offspring survival would make the survival of the mother......to produce more offspring.....more important.

    Fair enough. To repeat, I wasn't making an argument just floating some reasons why a fatal gene might exist.

    Peter Grant, Comment 15, quotes Richard Dawkins to show a route to fatal genes - they exist in all species but natural selection keeps them switched off (in later generations) to ensure that vehicles (individuals) have a chance to reproduce.

    In the Octopus species in question, if a fatal gene is switched on by laying eggs then that is very close to reproduction - but it is still post reproduction.

    For me that still leaves the question: Why are parents that die immediately after reproduction not outperformed by other species that nurture their young for longer?

    From that perspective I'm quite pleased with my hypotheses - they seem to dovetail nicely with Dawkins'.

    I will have a play with Darwinbots some time, thanks for that.

    Peace.

    Tue, 22 Nov 2011 10:48:51 UTC | #892239

    Alan4discussion's Avatar Comment 23 by Alan4discussion

    Comment 22 by Stephen of Wimbledon

    For me that still leaves the question: Why are parents that die immediately after reproduction not outperformed by other species that nurture their young for longer?

    I think the links explain that the vast numbers of eggs are cared for up to the point where they are widely distributed/scattered and parental care would be impossible.

    Following hatching the giant octopus young swim toward the surface and spend 4-12 weeks drifting in the plankton until they reach a size of >14 mm mantle length (still under 5 grams). The young then settle to the bottom, although not much is known about this settlement phase

    The adults and older offspring octopus live and shelter on the rocky sea bottom. Compared to many fish or Molluscs which lay eggs and abandon them, the octopus cares for its eggs for an exceptionally long time.

    Tue, 22 Nov 2011 11:48:26 UTC | #892253

    Phen's Avatar Comment 24 by Phen

    Well, assuming that the octopus' are simply incapable of reproducing a second time, for whatever reason, wouldn't the creatures that died quickly after reproducion give a distinct advantage to their young due to the lack of competition with fully grown adults? I also wonder what would happen if a parent encountered its own young, would it recognise it? Perhaps they would kill and eat them, unaware that its from their own spawn?

    Tue, 22 Nov 2011 15:11:00 UTC | #892308

    Alex, adv. diab.'s Avatar Comment 25 by Alex, adv. diab.

    Comment 18 by PatW :

    Does anyone know where "selfish genes" are located on genomes?

    They are self-centered, of course.

    Tue, 22 Nov 2011 15:54:05 UTC | #892329

    Michael Austin's Avatar Comment 26 by Michael Austin

    Considering how many eggs they lay, I would think that this is a distinct possibility.

    Comment 24 by Phen :

    Well, assuming that the octopus' are simply incapable of reproducing a second time, for whatever reason, wouldn't the creatures that died quickly after reproducion give a distinct advantage to their young due to the lack of competition with fully grown adults? I also wonder what would happen if a parent encountered its own young, would it recognise it? Perhaps they would kill and eat them, unaware that its from their own spawn?

    Tue, 22 Nov 2011 16:47:02 UTC | #892343

    Stephen of Wimbledon's Avatar Comment 27 by Stephen of Wimbledon

    In response to Comment 23 by Alan4discussion

    Thanks Alan, that certainly seems to cover most angles.

    Tue, 22 Nov 2011 17:16:31 UTC | #892355

    DavidXanaos's Avatar Comment 28 by DavidXanaos

    Comment 24 by Phen :

    Well, assuming that the octopus' are simply incapable of reproducing a second time, for whatever reason, wouldn't the creatures that died quickly after reproducion give a distinct advantage to their young due to the lack of competition with fully grown adults?

    Well, no according to the Wiki article the octopus stops eatign after giving birth, and the entire taking care time it leavs from reserves. When the self destruct glands are removed though live much longer the octopus still does not eat anything. Those they wouldn't be needer a threat nor a competition to their young.

    one thought I head was that at some point in the past the octopus acted as food sopply for their young after they hatched, and the self destruct was designed to prevent any possible defensive reactions.

    But is that possible? I mean is there a precedence for such a thing in nature?

    Tue, 22 Nov 2011 19:40:51 UTC | #892399

    pj's Avatar Comment 29 by pj

    This phenomenon of obligate dying after one reproductive episode is called semelparity and it is found in many species. All annual plants are effectively semelparous. The opposite life-history is called iteroparity. Here is a peer-reviewed web-resource for those interested in further learning:

    http://www.nature.com/scitable/knowledge/library/semelparity-and-iteoparity-13260334

    Tue, 22 Nov 2011 20:22:58 UTC | #892408

    DavidXanaos's Avatar Comment 30 by DavidXanaos

    Comment 29 by pj :

    This phenomenon of obligate dying after one reproductive episode is called semelparity and it is found in many species.

    So far so good, but to my limited knowledge usually the dying is a by product, they die of starvation or fatigue but only for octopuses I read that they actually have a self destruct gland and they life can be prolonged by many months by removing it.

    Are there other semelparous species that actually do not just exost them selves to the point of death (starvation or fatigue) but actually have a programmed cell death that can be turned off my an operation or drugs?

    My question is not about species that just die after finishing with reproduction. But about the special case where a species develops a organ that influences its live only after finishing reproduction. Also note that the species seams to nor show any behavior after finishing reproduction that would obviously be in any way a threat to its offspring. the octopus basically seam to just wonder around until it starves to death. So the question is how the genes for this particular feature get to be selected for.

    David X.

    Tue, 22 Nov 2011 20:39:35 UTC | #892413