favourite invertebrate

Discussion in 'Biology & Genetics' started by spuriousmonkey, Mar 19, 2003.

  1. ElectricFetus Sanity going, going, gone Valued Senior Member

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    Jolly Rodger,

    I guess your asking for a thrashing?

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  3. Jolly Rodger Banned Banned

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    Mr. Fetus What is a thrashing?
    i'm new at this place.
    please help
    HELP
     
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  5. ElectricFetus Sanity going, going, gone Valued Senior Member

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  7. cthulhus slave evil servant Registered Senior Member

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    the cuttle fish.
    theyr just so cute.
     
  8. BigBlueHead Great Tealnoggin! Registered Senior Member

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    And Cuttly!

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    Cute and Cuttly... ehe...
     
  9. Konek Lazy user Registered Senior Member

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    The eyes are inside the rhopalium. In cubic medusae the complex eyes may be able to form images (too bad they don't have brains to process them):
    http://www.mhhe.com/biosci/pae/marinebiology/casestudies/case_09.mhtml

    In other jellyfish the rudimentary eyes are just sensitive to light.

    Family: Physaliidae, Order: Siphonophora, Class: Hydrozoa, Phylum: Cnidaria.

    Each man of war is a colony of specialized polyps attached to a gas-filled bladder.
     
  10. Dr Lou Natic Unnecessary Surgeon Registered Senior Member

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    Thats right! I find that fascinating.
    They are a colony of organisms that all have different jobs.

    Which reminds me of ants, I forgot about ants, ants have to be my favourite invertabrate.
    They rule this planet with an iron fist.
    An ant colony is like a giant brain, chemical messages fire from ant to ant and the colony as a whole is one coordinated organism.

    Colonies are interesting because they completely release the pressure of natural selection on the individual. You'll find true altruism in colony animals, they no longer consider themselves priceless, the passing on of genes is not of an individuals concern because it is the whole colony that evolves as opposed to individuals, its survival of the fittest colony so they are completely and unquestioningly willing to kamikaze themselves for the good of the colony.

    Humans should have naturally been like this before they started living like a colony.
    We are all screwed up because we are still selfish mammals that want to pass on our own genes more than anything else, but we try to make a civilisation, and clearly its a sloppy mess, which is understandable when you consider the traits we are missing that would be required to make a civilisation work.
    Traits like those of the ants.
     
  11. paulsamuel Registered Senior Member

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    a biologist's perspective

    this is not true. it appears to be altruism and sacrificing for the good of the colony, but it is still individual selection because of inclusive fitness.
     
  12. Dr Lou Natic Unnecessary Surgeon Registered Senior Member

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    I better go fill EO wilson (aka the antman) in on this new information

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    It is not inclusive fitness because the fit are expected to sacrifice themselves, they would be unfit to not do so, and anyway they were never born to breed.
    A breeding ant is born to be a breeder and stays within the safe confounds of the colony.
    UNLESS we are talking about the colony passing on its genetic material which is where natural selection steps in, the individual ants are not pressured directly by natural selection, they need to do their job well in order for the colony to be successful and spawn new colonies. Most of them aren't going to breed no matter how long they avoid death.
    Doing their job well will often involve dying. Ants don't bite an anteaters nose and then run away, they clamp on so there will definately be no option but death. But these individuals clearly have not been cleansed out of the gene pool yet, why is that?
    That queen will continue to pump out all sorts of individuals suited to specific tasks, few of which will resemble what their father or mother are specifically designed to do, which is breeding.

    I don't even have an indepth knowledge of ants, I probably made a mistake there somewhere, what I do know is individual ants (the ones you see) are not being accounted for by ant evolution.
    The ants you see can live untill the die of old age, their success at life won't lead to their quality genes being passed on because that is not their task.
    Colonies evolve, individuals do not, even run of the mill cooperative pack animals aren't pressured by natural selection the same way solitary animals are.
    Ants are the extreme where their individual lives have no evolutionary significance at all.
     
  13. curioucity Unbelievable and odd Registered Senior Member

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    About colony...
    Well yeah.... for most invertebrates colony means size matters; greater army, more chance of surviving.... s o I agree......
    By the way, is it ALWAYS true that the smaller the members of the colony are, the more members are in the colony? Ants are small, and they are numerous..
     
  14. Konek Lazy user Registered Senior Member

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    Volvox are even smaller, and there aren't more than 500 individuals in the colony. By comparison, a queen ant can lay 1000 eggs or more per day.
     
  15. Konek Lazy user Registered Senior Member

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    Actually queens are subject to evolutive pressures. Their survival depends on breeding succesful workers.
     
  16. paulsamuel Registered Senior Member

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    an evolutionary biologist's perspective

    no need, i've spoken to him and he knows what i'm talking about, however you do not. the reason why it is still individual selection and not group selection is the amount of shared genes betwee the ants (inclusive fitness) where an individual ant's fitness is increased by sacrificing its reproducing and protecting those ants with whom it shares genes.

    it appears you need to look up 'inclusive fitness.' and perhaps read Wison's book on ants. other colonial organisms like bees and termites share this same evolutionary trend (including the colonial mammal, the naked mole rat) where individuals give up reproducing for the sake of protection and care of their reproducing siblings due to inclusive fitness. some search terms 'kin selection' 'altruism' 'inclusive fitness'
     
    Last edited: Sep 22, 2003
  17. Dr Lou Natic Unnecessary Surgeon Registered Senior Member

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    So we agree and you are just refusing to admit that this obviously means that the pressures of natural selection are not on the inidividual?
    The only naked mole rat who is subject to the pressures of natural selection is the male that goes on the long journey to find a new colony in which to plant his seed.
    Is that not correct?
    Therefore it is the colonies reproduction that is an evolutionary event.
     
  18. paulsamuel Registered Senior Member

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    reply

    no:

    kin selection and inclusive fitness allow us (evolutionary biologists) to explain, by individual selection, what appears to be group selection (which by the way doesn't exist)
     
  19. BigBlueHead Great Tealnoggin! Registered Senior Member

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    Ants and bees and other hive-type creatures are a bit of a special case for kin selection.

    Kin selection is an attempt to explain altruism between dissimilar individuals, and is (in my opinion) not the strongest argument in the world. You probably share 75 percent of your genetic material with the cow that you eat, but that doesn't stop you from eating it.

    Ants however, have a slightly different take on things because the workers are all parthenogenic clones of the queen. Hence the entire colony - to some extent - is an individual. When an ant dies to save the queen ant from the same colony, that's a much closer kinship than if you die to save your child, since the two share pretty much the exact same genetic code, where your child only gets half of yours.

    So, evolutionary pressures on ants have to be considered in this light.
     
  20. paulsamuel Registered Senior Member

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    reply

    it is an excellent argument and is accepted by biologists now, your opinion notwithstanding.

    you're misunderstanding the difference between sharing 'genetic material' and sharing genes. the genes are the source of the phenotype, upon which selection acts, and are only a portion of the genetic code. e.g. 2 individual humans share much greater than 99% of their genetic material, but if there is only ONE nucleotide difference at each gene, they share ZERO genes, therefore kin selection would not be relevant!

    bee and ant drones/workers (i.e. non-reproductive) are NOT clones of the queen! The reason hypothesized that they would forgo reproduction and sacrifice themselves for nest/hive defense is that they share 75% (on average) of their genes with their sibs (not 50% like other diploids). Its a reproductive strategy which only works because of the haplo-diploidy of the organisms.

    You may want to read up more on this in Behavioral Ecology, Krebs and Davies, 1st ed.

    Also try; http://www.utm.edu/~rirwin/391KinSel.htm
     
  21. BigBlueHead Great Tealnoggin! Registered Senior Member

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    Apologies for the clones bit!

    All the same, people have accepted kin selection a little too easily in my opinion; I am unsure whether it's reasonable to assume that an altruism gene can become fixed in a population when the beneficiary of the altruism is NOT necessarily carrying the altruism gene - hence, altruism represents a selective disadvantage when it is not prevalent in the population.

    That is, everyone would be willing to take advantage of the sucker who shares their food. Whether or not the bilkers would share the altruism allele is an open question.
     
  22. paulsamuel Registered Senior Member

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    882
    exactly!

    that's exactly why altruism doesn't exist, good point.

    with kin selection, we can show why it's NOT altruism. the action which appears altruistic is not, in reality, because of the benefits recieved by saving a close relative. i.e. sacrificing oneself by saving 2 sibs (each sharing on average 50% of your genes), one loses no reproductive capacity. one gains, if one can save 3 sibs, or 6 cousins, etc.

    This all leads into the theory of ESS (evolutionary stable strategy).

    a character that would increase the risk of losing reproductive capabilities for the benefit of others (increasing their chance of reproduction) is not an ESS (i.e. the character would be quickly lost in the population) unless those individuals which were saved carried many or most of the characters (including the character that puts reproductive capacity at risk) of the 'altruistic' individual. This is, in general, kin selection and the theory of inclusive fitness.
     
  23. BigBlueHead Great Tealnoggin! Registered Senior Member

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    Yes, but wouldn't "altruists" and "bilkers" eventually reach an equilibrium in the society? How do we get all the way to the hive? Or is that something that only happens by chance?
     

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