Expert: Walter Hintz - 3/19/2010

Question
QUESTION: Mr. Hintz,

It is interesting to me that the animal Hydrozoa can go from young to mature at will. This changes what I think about aging since I always thought it was the inevitable. Also, wouldn't it be like suicide if an animal changes back to a young Hydrozoa since young animals are easy prey? What do you think? Thanks!

Mark

ANSWER: Hi Mark; You will have to explain to me what you mean by changing from young to mature at will. Are you thinking about hydroid and Medusa stages?
First of all I do not believe that hydra have any "will" and secondly the terms young and mature are arbitrary.  Is aging inevitable? Not always. Recall that I told you that asexually reproducing organisms do not age but they have an immortality. They do not die they just undergo fission. The hydra reproduces sexually and asexually by budding

---------- FOLLOW-UP ----------

QUESTION: Mr. Hintz,

Sorry about that that, I should have proofread my message. Anyway, as far as Hydrozoa or more specifically Turritopsis nutricula, I got the sense from Wikipedia (which I know isn't a great source all of the time) that they could change back and forth based on this line: "The Hydrozoan species Turritopsis nutricula is capable of cycling from a mature adult stage to an immature polyp stage and back again. This means that there may be no natural limit to its life span. However, no single specimen has been observed for any extended period, and it is impossible to estimate the age of a specimen." from this page: "List of long-living organisms." I also should have been more clear and said that I thought the aging process for animals (not all organisms) is almost inevitable. Thanks for taking the time to answer my questions.

Mark

Answer
Interesting! I have heard about the immortal jellyfish often stated as the world's only immortal animal. Actually it is not because prokaryotes and many asexually reproducing protozoa are immortal. With this jellyfish the immortality occurs only within certain cells of the animal.
 I just read something that you might find interesting.  The US Fish and Wildlife surface is finding that due to global warming some bird species are getting smaller with shorter wings. There is a concept called the Bergmann rule which states that animal size is related to climate with animals "becoming" smaller in warmer climates. (note my asterisks around becoming) This does not explain elephants very well. Actually the Bergmann rule involves the surface area - volume ratio. Animals like polar bears living in cold climates tend to have a larger mass with less body surface area thus generating more heat with less heat loos through the skin. Animals like the giraffe are tall with a lot of surface and less bulk.

Anyway can we explain changes in birds by natural selection? This seems strange to me.