Two be or not two be?

[Fishteacher73]

There has been some discussion among some friends of mine about the nature of what constitutes an organism and the lifspan of said organism. This is not really problematic in animals that do not reproduce in asexual manners. The question arises specifically with organisms that "reproduce" with asexual fission or fragmentaion, such as many of ths SPS corals like Acropora, Montipora, etc. (There are a number of organisms that can reproduce through fragmentaion, but that is not a primary method (such as a planarian or many starfish)).

 

So the question that arises is: Is the fragment considered part of the original organism, or does it constitue a new organism, and if so, why?

 

Theoretically you could have "undying" lineages of these species...

 

Thoughts or ideas? :)

[bumab]

When an asexual animal buds (or splits or whatever), it still must duplicate it's DNA. That duplication contains mistakes and mutations, such that even big colonies of clones ARE genetically different, just not different in any important manner, since most major mutations are selected against. It's the same idea as a sexually reproducing organisms, however change happens on a much slower time scale.

 

So I would say the normal lifespan applies. Parent and offspring are still different, just to a much smaller degree.

 

Interestingly, this would lead towards the selection for sexual reproducing organisms, because they can adapt to change far quicker. That's a possible contributor to why most animals have short lifespans (less then 10 years).

[alxian]

for the purposes of my novel i research this topic in depth

 

i have yet to move on to the core nature of parthenogenesis. what i want (to know) is that animals that bud and split have more than enough DNA to create an individual without duplicating their own DNA perfectly.. not to say that that animal will have 100% of the species dna that precludes some other important facets of evolution i'd rather not leave out of my fiction (which must retain and preserve fact as much as possible = textbook fiction).

 

ideally i'd like to know that the animals that clone themselves have more than enough dna that they can reproduce enough individuals to restart a colony with very few individuals, meaning that these creatures have reached a point where evolution is pointless and wasteful of their resources. but for newer creatures that face exctinction daily like mammals its necessary for evolution to carrying on between generation and even within the individuals lifetime (the DNA of the child grows (mutates) during life).

 

the only question then is which evolved first cloning or sexual reproduction? does it matter? which is better for propagating genetic distinction?

 

i'd have to say sexual propagation is best.. but only when communication of that genetic distinction is great enough that silly geographic distinctions don't evolve. after humans harnessed flight and now that the global economy has peeps of all sorts flying around the country and mixing their pollen around everywhere i'm wondering how long such regional distinctions will last.. a few centuries more maybe? or until a global government mandates a perfect genome where such distinction will no longer be possible and distinction then will be up to the individual not the region... who knows... my vote is for now with the 'prefect genome' global incentive.

[Fishteacher73]

The fragmenntation I was speaking about, occurs in multicellular organisms. In the SPS (Small Polyp Stony) corals, while they do reproduce sexually,this is one of the major methods of propogation (pobably a better term than reproductyion in this case) is fragmentation (When largerer pieces of the main coral body are broken off and start to grow a new colony. This would be similar to the idea of cutting off your arm and it growing into a new you). So yes, there is cellular growth and reprodauction, but there is not a medusa (free swiming jellyfish like) stage in this method of propogation. This would be like your arm growing into an adult, not going through the developmental stages in youth. So I think my questions are valid.

 

1) So do you have a new organism when this occurs?

 

2) Through this process would you not get an "undying" organism?

[bumab]

Interesting... Like seeding starfish, which we do around here... It does sound like an undying organism. Good way to go really, the selfish genes win completely in that situation.

[MortenS]

The whole concept of an organism kind of breaks down when we are speaking about modular organisms

 

For example: The organism can be considered as a population, as well as an individual.

 

There are specific terms developed to deal with modular organisms.

 

A genet is the organism that develops from a zygote, and is the genetic individual, while a ramet is the organism that develops vegetatively through budding off the genet.

 

One genet can consist of several ramets, and can be spread over a great distance, even separated from each other.

 

Using this definition, even bacteria could be viewed as an enormous genet, divided into millions of ramets.

[alxian]

speaking of such separations. what do you make of the claim that budding cells off of humans (by actually cutting flesh from the individual, stays in communication with the whole?

 

it may be a myth and i can't find the link after searching but i'm wondering if there is any truth to it.

[MortenS]

I have not heard about that, but if you think about socalled phantom limbs, it is caused by the nerves that got cut off. E.g. if you cut off your arm, the nerves leading from your fingers up to the spine and brain get severed off, but will still send information that your brain percieves coming from the fingers. It is therefore possible to feel itching and similar sensations on a limb that is cut off. This is not because the severed limb has any itch, you can incinerate the severed limb, and the patient will still experience the phantom limb.

[Fishteacher73]

For example: The organism can be considered as a population, as well as an individual.

 

 

We debated what the line was on this issue, and whether it was really of any use. Is there really any scientific meaning in breaking up an individual and a population?

[MortenS]

well, if you consider certain plants that propagate via root shoots as well as with sexual reproduction, it is definetly of interest, at least for biologist. The genet may cover a very large area, and individual genets may be of considerable distance from each other.

 

The population of ramets is however what we see when we observe nature (without doing any genetic analysis).

 

If you study population dynamics in modular organisms, it is definetly of interest to know whether you are dealing with genetically different genets, or genetically identical ramets.

 

It is only when you use the organism concept we apply on unitary organisms on modular organisms you have a problem separating between individual and population.

[alxian]

humans are then without a doubt genets even though the drift between us is minimal and solitary humans will still behave similarly to other humans only the complexity of the tasks they accomplish differs. or have i got that mixed up?

[MortenS]

All unitary organisms (such as humans) can be considered genets (except perhaps for monozygotic twins, which are natural clones, and therefore fulfill the ramet definition).

 

Eventually, we come to a point where we realize that however much we try, nature does not allways want to fit into our definitions...

[Fishteacher73]

BAD NATURE!

 

Back into the box!