Open circulatory system pro

Question

Hi!

I have found this advantage for open circulatory system, but I do not get it:

3. Body temperature control is better.

Open circulatory systems can dispel heat more efficiently, which makes it possible to live in a high temperature environment. In colder temperatures, heat can be maintained if shelter can be found.

What does it mean? Why can open circulatory system dispel heat better than a closed one?

Answer 1

Hi Lily P.,

Frankly, I don't get it either. Open circulatory systems are found in earlier-evolved creatures such as molluscs and insects. Conserving and/or dispelling body heat is not particularly their problem, since they are cold-blooded; therefore, they wouldn't waste energy trying to actively heat or cool themselves. Whether they are warm or cool doesn't matter much to them, except in terms of trying to capture food or avoid becoming someone else's lunch. So, they wouldn't want to be creeping slowly on a tree limb under the eye of a hungry bird, for example! But in terms of hot: they can function quite nicely in temperatures that would lay you out flat. Some desert-adapted ants, for example, function well at 50 C, or slightly above. It's a question of their body enzymes denaturing or not,and their behaviors (ambient temperature varies widely according to distance from the ground) NOT whether they shed heat efficiently or not. Sometimes they may generate heat by vibrating their wing muscles (moths and bees), but that would argue for conserving the heat locally in the muscle, not dissipating it quickly to the rest of their body!

The big advantage of open circulatory systems is, they are simpler (fine as long as nobody bites you in half!), and use less energy to run (great, if you are on a limited energy budget -- example, mayflies, which don't eat at all as adults, or molluscs, which must keep filtering in hopes of getting some food).

-- Cheers, -- Mr. d.