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Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: Chemistry4me on 18/03/2009 06:26:01

Title: Why are some organisms more tolerant than others?
Post by: Chemistry4me on 18/03/2009 06:26:01

Why are some organisms more tolerant than others?
Why are they more tolerant than others?

Title: Why are some organisms more tolerant than others?
Post by: Kryptid on 18/03/2009 23:05:20

Tolerant to what? Heat? Dryness? High pressure?

If one assumes that an organism is adapted to its environment, then one must also assume that an organism is adapted to presence (or absence) of changes that regularly occur in its environment.

Let's say that you have a single-celled organism (Cell A) that lives in a particular liquid medium that stays at a fairly constant temperature year-round. Then you have a second cellular creature (Cell B) that has to endure much higher and much lower temperatures year-round.

Cell B will need to be able to produce certain proteins or other chemicals that will allow it to deal with these temperature changes when they occur. Otherwise, it will die. Cell A, which has an unchanging environment, will simply not need that kind of flexibility. For that reason, it can utilize its organelles and protein synthesis for other uses that may be more important in increasing its fitness. Cell B therefore has to make compromises that Cell A did not.

Now let's say that you put Cell A and Cell B in an unchanging environment. Since Cell A has a design that is maximized for efficiently living in an unchanging environment, one could expect that it would outcompete Cell B. Therefore it is more "fit" than Cell B in this environment.

Now turn the tables.

Put both cells in Cell B's environment and Cell A is going to have problems dealing with the temperature changes. It might not even be able to survive at all. This is where the flexibility of Cell B will give it the superior fitness.

In conclusion, an organism can lose adaptive advantages (such as temperature tolerance) if there are no selective pressures to keep those traits in the population. Take dogs, for example. Some dogs have been bred so far from their wolf ancestors that they could not survive in the wild. Yet, because they live in human company with a constant food supply and medical attention, they do not need those traits. To them, it is basically "extra baggage" that can be dispensed with.

Title: Why are some organisms more tolerant than others?
Post by: Chemistry4me on 19/03/2009 05:43:48

Thank you Supercryptid [:)]
You have explained it very clearly.