Why Two Sexes?

[Polymath257]

A species of African frog comes to mind. I forget it's name though. Also, I recall some salamanders might be able to reproduce asexually.

By the way, remember that in amphibians and reptiles, the sex of an individual is determined by environmental factors. Not sure about birds. It's been a long time since a biology professor has sat me down to lecture me about the birds (and the bees).

There is a species of lizard in the Southwest of the US that only has females. They reproduce by parthenogenesis and have 'pseudocopulation' between females. No fertilization occurs.

 

[Double Fine]

A species of African frog comes to mind. I forget it's name though. Also, I recall some salamanders might be able to reproduce asexually.

I was thinking about the frogs too. I may be wrong here (or have the cat by the wrong tail) but don't they sort of like flip between genders? I.e. when there are too few males, a female might turn male.

If anybody can help us with species names, I would be much obliged.

By the way, remember that in amphibians and reptiles, the sex of an individual is determined by environmental factors. Not sure about birds.

yes for amphibians and yes for some reptiles and yes for birds too. The ZW system, yes?

It's been a long time since a biology professor has sat me down to lecture me about the birds (and the bees).

That was a good one

 

[Double Fine]

Yes, quite a few. Many plants (strawberries have runners, for example), can reproduce asexually while also having seeds for sexual reproduction. Sponges and hydras are animals that can reproduce both ways.

Thanks Polymath, I'd look it up. I had no idea that one species could do both

 

[Double Fine]

There is a species of lizard in the Southwest of the US that only has females. They reproduce by parthenogenesis and have 'pseudocopulation' between females. No fertilization occurs.

I just googled that. It's the New Mexico Whiptail.

That would be an example of asexual reproduction, yes?

 

[Polymath257]

I was thinking about the frogs too. I may be wrong here (or have the cat by the wrong tail) but don't they sort of like flip between genders? I.e. when there are too few males, a female might turn male.

If anybody can help us with species names, I would be much obliged.

A quick search provided this link: Can Amphibians Change Their Sex?

yes for amphibians and yes for some reptiles and yes for birds too. The ZW system, yes?
That was a good one

The ZW system is like the mammalian XY system, only in reverse. So, in mammals females are XX and males are XY (females homomorphic, males heteromorphic), in birds the female is ZW and the male is ZZ (females heteromorphic and male homomorphic).

 

[Polymath257]

I just googled that. It's the New Mexico Whiptail.

That would be an example of asexual reproduction, yes?

Yes, although the pseudocopulation complicates matters--they do have sex, but it is irrelevant for the genetics. I may stimulate the necessary ovulation, though.

 

[Double Fine]

A quick search provided this link: Can Amphibians Change Their Sex?

The ZW system is like the mammalian XY system, only in reverse. So, in mammals females are XX and males are XY (females homomorphic, males heteromorphic), in birds the female is ZW and the male is ZZ (females heteromorphic and male homomorphic).

Yes and that lets my mind go to a different topic altogether.

So our ancient ancestors are the synapsids, right? They showed up 300 million years ago, dominated the earth and then suffered huge losses during the Permian Extinction.

Those synapsids were obviously very reptile-like still, and would have used the ZW system. At what point would we have changed to the XY system and why? Was it to facilitate live birth? Was it due to our much diminished size after the big extinction event? Or was it when we became warm blooded?

 

[Sunstone]

See guys! See! Not all my threads are dogs. I can create fun threads too! See!

 

[Double Fine]

Yes, although the pseudocopulation complicates matters--they do have sex, but it is irrelevant for the genetics. I may stimulate the necessary ovulation, though.

That's freakin' weird. But, very informative.

I may stimulate the necessary ovulation, though.

I know that the "I" is a typo here.. but this was a humourous one.

 

[Double Fine]

See guys! See! Not all my threads are dogs. I can create fun threads too! See!

I awarded you a gold medal for granting us a nice pastime on this Sunday afternoon

 

[Vinayaka]

Not sure i could handle more than 4 or 5


I guess other than asexual reproduction 2 sexes is the most efficient use of cells.

I've always thought it would be better with a bunch, and all of them necessary to reproduce in some sort of co-operative fashion. That would separate the fools from the wise, and only the best genes would be passed on. It would be a fun challenge.

 

[exchemist]

In essence, your thinking parallels the currently most respected hypothesis in the field.

It does?

Mind you, in his novel "The Gods Themselves", Asimov imagines beings that are formed from an interaction of 3 sexes: male, female and parent. The names of 3 characters are Odeen, Dua and Tritt, which I seem to recall are Russian for one, two and three.

But the novel isn't about that. It is just incidental, to make them seem more alien.

 

[Polymath257]

Yes and that lets my mind go to a different topic altogether.

So our ancient ancestors are the synapsids, right? They showed up 300 million years ago, dominated the earth and then suffered huge losses during the Permian Extinction.

Those synapsids were obviously very reptile-like still, and would have used the ZW system. At what point would we have changed to the XY system and why? Was it to facilitate live birth? Was it due to our much diminished size after the big extinction event? Or was it when we became warm blooded?

My *guess*, and it is purely a guess, is that they probably determined sex by environmental signals and that the XY system (and the ZW system) came later.

Unfortunately, we may never know on this issue. This doesn't preserve well in the fossil record and no good comparison species currently exist as far as I know.

I just did a quick check to verify that marsupilas and monotremes use the XY system: they do.

 

[Double Fine]

I've always thought it would be better with a bunch, and all of them necessary to reproduce in some sort of co-operative fashion. That would separate the fools from the wise, and only the best genes would be passed on. It would be a fun challenge.

I think you would struggle to get the best genes in that scenario.

Right now, you have a female that requires a suitor to fight to the death/perform some dance/build a nest/buy her dinner and thereby proving his worth. Problem is that if there is another link in the chain, how do you know that you've got good genes in there? Sperm might be easily discarded and dispensed because of how cheap it is, but eggs are very rare and valuable.

Yes, you have a wider gene pool with a trisexual arrangement, but I think that comes at the cost of complexity and a lack of control over what genes actually go into the gene pool.

 

[exchemist]

Yes, quite a few. Many plants (strawberries have runners, for example), can reproduce asexually while also having seeds for sexual reproduction. Sponges and hydras are animals that can reproduce both ways.

So do some protozoa: paramecium for example.

 

[Polymath257]

Yes, you have a wider gene pool with a trisexual arrangement, but I think that comes at the cost of complexity and a lack of control over what genes actually go into the gene pool.

Am I the only one that thinks of Asimov's story 'The Gods Themselves' when discussing the possibility of trisexuality?

 

[Polymath257]

So do some protozoa: paramecium for example.

Yes. I was going for multicellular examples, but single celled examples are common.

 

[exchemist]

Yes. If I may add to this, there are pros and cons associated with the amount of genders involved.

The fewer the genders, the easier it is to reproduce, but you are limited to a smaller gene pool. The more genders there are, the more genetic information is available, but that comes at the cost of complexity.

Asexual reproduction has the benefit of simplicity, but it's drawback is that very few traits can be added. Trisexual, Quadrisexual etc (?) reproduction would have the benefit of a varied gene pool, but comes at the immense cost of complexity.

Sexual reproduction, on the other hand, allows for a huge amount of genetic information in the gene pool, especially when we compound that over multiple generations. It is also fairly simple, requiring only one male and one female.

I suppose, too, that 3 sexes would require some complicated genetic system in which chromosomes were arranged in threes instead of pairs. So probably the evolution of that would take longer and it is a bit hard to see what advantage it would confer, to outweigh the simpler system of pairs.

 

[Sunstone]

Am I the only one that thinks of Asimov's story 'The Gods Themselves' when discussing the possibility of trisexuality?

Never read the story. But now that you've mentioned trisexuality, I've gotten all hot and bothered.

 

[exchemist]

Am I the only one that thinks of Asimov's story 'The Gods Themselves' when discussing the possibility of trisexuality?

No. See post 52.