Symmetrical Animals: Nature & The Fiddler Crab?

[Anonymous]

On telly today there was a prog about Fiddler crabs and it struck me i couldnt realy think of any animal that was so asymetrical... fiddler crabs have (well the males anyway) one huge claw used for mateing display... how is this handled in thier DNA/Genes?... after all i presume that symetry is handled by it saying in its program...do the same only mirror it.... anyone know anything about this sort of thing?

 

[marion]

I did see a program a few years ago about a new fossil found on an assymetrical sea creature that was thought to be the ancestor of a lot animals around today , at least vertebrates I think . They thought the assymetry of the animal explained the assymetry of our and other animals's internal organs. Don't know how to relate that to the fiddler crabs conundrum , but it is interesting and does show that we are not really as symetrical as you might think .

 

[_schnor]

Fiddler crabs aren't profoundly asymmetrical as compared to other species, it's just that one claw is significantly larger than the other - like you mentioned it's largely redundant except for mating displays, and probably arose through chance mutation/adaption a few million years ago, but yes almost every organism is inherently symmetrical.

Imagine cell multiplication as two sets of numbers: -

1 2 4 8 16 32 64 128 258 512 1024, etc
1 2 4 8 16 32 64 128 258 512 1024, etc

Given enough generations, the numbers will be arbitrarily high (in terms of cell numbers) that if one set of numbers skips a doubling, the resulting numbers will be marginally different, so the two sets will be roughly the same amount (e.g. size), so making the organism symmetrical - from what I remember from A level biology anyway

However, nature always finds a way to contradict a set pattern, so if you want whacky creatures, check out the Burgess shales :eek!!!!:

 

[Anonymous]

i read the book on the Burgess shales and well wacky or what!..... I know the fiddler carbs claw is virtuly just a bigger version of the other, but surely thi shas implications for other outsize cell growth like cancer?.... surely it has a start and a stop gene?....

 

[rynner2]

I recently bought an old New Scientist for 10p in a charity shop. (17.6.2000) By chance it has an article on embryonic development, and although our insides are normally asymmetric, some people are born back to front (liver on the left, etc). This is called Situs Invertus. They may never know unless they have to go for an X-ray or an operation.

Worse off are those whose insides ARE symmetrical - they ususally have 'plumbing' problems. There are two forms of this:- Left and Right Isomerism. No doubt googling on those terms will turn up more info.

But even our symmetrical bits are rarely exact. Faces are not symmetrical, and making a mirror image of each side of a pic of your face and joining each reflection to its original to make a truly symmetrical face, actually produces two different faces. (This is easy to do with graphics software.)

 

[Anonymous]

i presume the overall symetry is a kind of shirt hand. so that agene or DNA chain can produce a twice as big animal for a certain string... the unsymetry of superficiely mirrored thinsg like faces is interesting i wounder what causes it, is it acumulated falts in DNA?... one would expect that if it was that it would cause and end to an awful lot of pregancies... perhapse thats what early lose of pregnancy is about?..... or is it just the imperfect way that DNA works...more hit and miss than we suspect?

 

[_schnor]

I think this is one of the questions that genetesists are still trying to figure out. IIRC 90% of all foetuses (of every species) have genetic abnormalities, but somehow they get sorted out in the womb in 99.9% of cases

I reacon it verges on the spiritual TBH

 

[Anonymous]

But even our symmetrical bits are rarely exact. Faces are not symmetrical,

I read somewhere, or I might be making it up, that the most successful people such as actors, film stars, etc, have faces which are more symmetrical than normal.

 

[Anonymous]

On telly today there was a prog about Fiddler crabs and it struck me i couldnt realy think of any animal that was so asymetrical

Flatfish are very asymmetric- they start off like other fish fry, but one eye migrates to the other side of the body, and they end up lying on one side for the rest of their life.

 

[Anonymous]

I read somewhere, or I might be making it up, that the most successful people such as actors, film stars, etc, have faces which are more symmetrical than normal.

I have seen research that seems to show the opposite. They took attractive people and mirrored the left or right side of their face and they looked bland and boring. We seem to find small imperfections attractive, perfection merely acceptible.

The exception is Audrey Hepburn who was almost perfectly symmetrical and was rated as very attractive. No explanation was ever put forward to my knowledge...

 

[Anonymous]

A company I used to work for wrote message matching sofware. The symbol they used for this program was a type of tree frog which is, apparently, completely symetrical, internally and externally. Blowed if I can remember what species it was though.

 

[rossba1]

symmetry in organisms is a subtle interplay of genetics and other controlling hormones and chemical messengers. For example i read about some species of newt/salamander that was being used as a developmental model and they discovered that if you removed half the cells in one of its limbs then left it to grow it didnt become a smaller leg, or undergo a rapid burst of cell division, the cells just grew twice as big until the whole limb was as large as its opposite.
Situs inversus is an interesting condition which i studied a bit for a course on genetic basis of disease. Kartageners syndrome patients have a 50:50 chance of having situs inversus because they have a mutation in a dynein molecule that affects the cilia (hair like proteinaceous molecules present on some cells, and inside some too). Dyneins act as molecular transporters, ferrying around associated molecules within the cell along a molecular track of a protein called actin. In kartageners the current thinking is(was?) that the dysfunction of this motor prevented the proper diffusion of a molecular gradient acroos the early embryo that set up the proper asymmetry of the internal organs. This asymmetrical distribution of the molecular gradient, without dynein is left to chance and so can run either left-right or right-left, according to chance and this leads to the 50% of situs inversus in kartageners syndrome.

 

[Anonymous]

Flatfish - now that's a weird one - i guess the fish that could see well whilst lying on it's side was the most successful and bred more, thereby ensuring that future flatfish (in time) were flat with both eyes arranged asymmetrically - still looks blimmin odd, tho.