[Karen W. (OP)]

Well, since I was curious about the fish, I figured what the heck.. I'll ask about the other male animals in nature also!

[another_someone]

All animals need to have some mechanism to make males, and I know of no other mechanism than the use of testosterone, although I don't know if that is also what is used by insects or other invertebrates.

Birds certainly use testosterone (this is what causes a male bird to sing), and so do mammals, and clearly also Betta fish - so I suspect that at least it is the mechanism used by all vertebrates, but I would not be surprised if it was conserved even amongst invertebrates.

[Karen W. (OP)]

Thanks George , after Stefan answered I felt it was probably true of most animals and such.. Thanks so much for your response.

[kdlynn]

wouldn't the mechanism be the other chromosome though? how does testosterone make a male a male?

[Karen W. (OP)]

Good Question.. I haven't a clue.. but Stefans fish sites said the injected these female betta's for several weeks and they took on all the features of the male including I think it said aggressive behavior and after the injections stopped they still maintained the male traits so there was referrals to changing the sex ....I think that was very interesting and if they can do that to fish etc.. havent they done similar things in humans!

[OstateStudent]

I think it is the chromosome which physically makes a male. Testosterone injections can induce male behavior,as well as some physical characteristics,  but not actually change the organism from female to male.

[OstateStudent]

Also, they do currently use testosterone and estrogen with transgender post/pre operative humans to help them achieve a more realistic opposite sex appearance. But all the testosterone in the world won't allow a female to mate and succesfully have offspring with another female =)

[another_someone]

wouldn't the mechanism be the other chromosome though? how does testosterone make a male a male?

What is interesting is that not all animals use the same chromosomes to denote gender.

I suppose the real answer to your question is what is maleness?

Certainly, in many animals, testosterone has been shown to change brain structure, hence giving an animal testosterone will make it behave in a more male fashion (hence make a songbird sing, make an animal more aggressive, etc.).

It is also wrong to assume that testosterone is only produced in males.  Certainly in humans (and I suspect in all animals), both males and females produce testosterone, but males produce much more of it - hence females have some male characteristics (like aggression, including sexual aggression), but while both males and females cover a spectrum of maleness in their behaviour, males will have far more testosterone, and far more male behaviour.  Also, females who have excessive testosterone, aside from possibly having more male psychological characteristics, are likely to have more facial hair.

My own suspicion is that much of the modern social pressures towards suppressing male aggression is partly responsible for the supposed modern reduction of sperm counts in males, as it reduces their 'maleness'.

It seems to me to be clear that testosterone cannot actually be encoded on the sex chromosome (i.e. the Y chromosome for mammals), since this would preclude females from producing testosterone, and would prohibit other animals that do not have a Y chromosome from producing testosterone.  Rather, the Y chromosome actually has very very few genes on it, but rather, it creates a cascade of reaction with genes on other chromosomes, and it is they that actually produce the testosterone.

As to whether testosterone will produce male gonads - I think (although maybe someone will correct me) that it is responsible both for creating male gonads, and for the suppression of female physical features; but the effect depends upon the exact moment that testosterone is acting on the body, and once the fetus has passed a certain stage of development, that particular feature cannot be reversed (some species of fish I believe can change from being male to female in adult life, but mammals and birds cannot do that).

[kdlynn]

very informative everybody

[Karen W. (OP)]

 It is also wrong to assume that testosterone is only produced in males.  Certainly in humans (and I suspect in all animals), both males and females produce testosterone, but males produce much more of it - hence females have some male characteristics (like aggression, including sexual aggression), but while both males and females cover a spectrum of maleness in their behaviour, males will have far more testosterone, and far more male behaviour.  Also, females who have excessive testosterone, aside from possibly having more male psychological characteristics, are likely to have more facial hair.[quote\]

OH my Gosh....George so that's what's wrong with my chin all this time!!! 

[_Stefan_]

But all the testosterone in the world won't allow a female to mate and succesfully have offspring with another female =)

Interestingly, in Betta splendens at least, females that have had testosterone treatment are able to mate with other females and produce viable young! However, all the offspring from such matings will be female, as they inherit no male genetic material.

The testosterone-treated females developed testes, spermatocysts and produced sperm.

[Karen W. (OP)]

I thought I read something like that in one of your links Stefan! Thanks.. That is interesting!