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latsot
Skeptic Friend
United Kingdom
70 Posts |
 Posted - 06/18/2005 : 12:20:50 [Permalink]
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quote:
Originally posted by Dave W.
quote:
Originally posted by latsot
I'm just having trouble understanding how sexual selection could occur without sexes.
Easy: you have a trait which makes you "hot" to all the other individuals. If a trait makes individuals prefer to mate with only those carrying that trait, it doesn't matter if there's only one sex, two sexes or 17 sexes, it'll be selected for based on mating habits, and perhaps nothing else.
Im not convinced - sexual selection is more complex than this. For example, the *preference* for that trait also has to be heritable. This is part of what makes the dynamics interesting - the interplay between the preference and the trait. I don't think this scenario would show that.
There is other stuff too - and still the interesting parts of sexual selection haven't really been touched upon.
Cheers
r |
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Dave W.
Info Junkie
USA
26020 Posts |
Posted - 06/18/2005 : 20:02:07 [Permalink]
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quote:
Originally posted by latsot
Im not convinced - sexual selection is more complex than this. For example, the *preference* for that trait also has to be heritable. This is part of what makes the dynamics interesting - the interplay between the preference and the trait. I don't think this scenario would show that.
Sure. A trait, and a preference for that trait (as another trait), which are both heritable. What's the issue? One would think that even in a species without mating displays, simply being attracted to other individuals of the same species would be sexually selected. Spiders which try to mate with birds would be selected against, fairly strongly.quote:
There is other stuff too - and still the interesting parts of sexual selection haven't really been touched upon.
For example? |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
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latsot
Skeptic Friend
United Kingdom
70 Posts |
Posted - 06/19/2005 : 02:02:04 [Permalink]
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quote:
Sure. A trait, and a preference for that trait (as another trait), which are both heritable. What's the issue? One would think that even in a species without mating displays, simply being attracted to other individuals of the same species would be sexually selected. Spiders which try to mate with birds would be selected against, fairly strongly.
I'm obviously not expressing my point very well. I don't think your example is sexual selection as the term us normally used - it looks like plain and simple natural selection to me (not that natural selection is either plain or simple :-). Although the evolution of sex itself is a difficult topic and I probably shouldn't pass off the example quite so glibly.
Anyway - sexual selection is partly about competition for mates - something your example doesn't cover explicitly. Peacocks evolve ever more elaborate tails in a bid to attract peahens, who might evolve ever fussier tastes. The point is that this war of attrition between the sexes develops traits that are not adaptive in the traditional sense - in fact, they might be detrimental in some ways to that species. For example, bright colours might increase risk from predators, moose antlers take a lot of energy to grow and cart around etc. and so these would be unlikely to occur through natural selection alone. Sexual selection can drive such adaptations despite potentially or at least apparently maladaptive effects.
Could this occur with one sex? Its tempting to say yes: as you point out, the sexually-selected trait (fancy tails, for example) could occur to some extent in all members of a single sex species, as could the preference for that trait.
There is something unconvincing about this, however. I'm not convinced that such a scenario would occur.
When I said 'competition for mates' earlier, I wasn't suggesting that there aren't enough of one sex to go around. I'm saying that in sexual species, it makes sense for the partner putting the most resources into reproduction to be fussy. In many species, the male puts in less resources than the female and can have many, many more children. It therefore makes evolutionary sense for him to mate with as many females as possible. Similarly, it makes sense for the female to be fussy - she has to make sure she is getting a good quality male - whatever that might mean in the particular circumstances.
In some species, attentive fathers may be desirable and elaborate courtship might be a mechanism to achieve this - to artificially increase the male's investment in that particular set of offspring. If he's spending his time dancing or nest-building, he won't have time to go and court other females. All his eggs are in one basket, so it would make sound evolutionary sense for him to be attentive to the offspring.
Whatever - the reason sexual selection occurs in this case is that the balance of power between the sexes is uneven. Sexual selection has evolved as a way to level the playing field. I suspect this is true in all cases of sexual selection. Which would imply that more than one sex is required for sexual selection to occur.
It could be argued that hermaphrodites are single sex species, but that sexual selection might make sense for them. I can see how this might be the case, but my argument still applies - at any point in time, an individual is acting 'as' a male or a female. It would presumably take some convincing to act as a female in any case, when the 'best' strategy is probably to convince another individual to act as a female. So there seems a good avenue for sexual selection here.
In a species with no sexes (or equivalently) one sex - I would not expect to see an uneven balance of power and so would not expect to see sexual selection either. This may be an oversimplification though. There is a case for suggesting that traits that explicitly display some measure of quality might be attractive - this could be heritable and the preference for that trait also heritable. I have my doubts about whether this would be a stable strategy, however. The payoff for cheating would be extremely high, for one thing. I doubt there would be a basis for the development of maladaptive traits over long periods of time.
Some of this is speculation of course and as far as I'm aware, this matter is far from settled - there are still a lot of arguments about sexual selection.
quote:
quote:
There is other stuff too - and still the interesting parts of sexual selection haven't really been touched upon.
For example?
Oh, loads of stuff. For example, the question of why sexually selected traits occur in the first place. Are they a measure of quality, as some people think? For example, the lack of human body hair might be sexually selected because it makes it obvious whether a potential mate has skin parasites. Or are they purely arbitrary (as Darwin thought)? Perhaps the preference for hairless mates has no particular reason at all. Perhaps the trait itself is unimportant as long as it proves maladaptive in some other way (moose's antlers as a sign of quality - it survives DESPITE the antlers, so must be a pretty good moose).
Anyway, these are the really interesting questions in sexual selection, but I assume would be outside the scope of most simulations.
Possibly more amenable to simulation is the effect sexual selection has on the dynamics of species interactions.
Anyway, a bit rambly and I seem to have conceded both sides of the argument to some extent, but I hope this helps.
Cheers
r
edited to correct retarded format, r. |
| Edited by - latsot on 06/20/2005 03:40:24 |
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Dave W.
Info Junkie
USA
26020 Posts |
Posted - 06/20/2005 : 06:45:05 [Permalink]
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quote:
Originally posted by latsot
I'm not convinced that such a scenario would occur.
I agree with most of what you say, I think our disconnect centers on the above-quoted statement. I'm not trying to suggest that sexual selection in a single-sex species would occur, I'm just convinced that it could occur.quote:
It could be argued that hermaphrodites are single sex species, but that sexual selection might make sense for them. I can see how this might be the case, but my argument still applies - at any point in time, an individual is acting 'as' a male or a female.
Actually, with earthworms, they line up side-by-side, head-to-tail, so that they couple male parts to female parts both at the same time. Some hermaphroditic snails also impregnate each other simultaneously. In neither case does one of the pair "act" as either male or female. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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latsot
Skeptic Friend
United Kingdom
70 Posts |
Posted - 06/20/2005 : 09:15:11 [Permalink]
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quote:
I agree with most of what you say, I think our disconnect centers on the above-quoted statement. I'm not trying to suggest that sexual selection in a single-sex species would occur, I'm just convinced that it could occur.
OK. I won't argue about that. And I'll think some more. I agree that in theory something like sexual selection could take place with a single-sex species. But I still suspect there is something different to sexual selection going on in this case. I'll have a think about it.
quote:
Actually, with earthworms, they line up side-by-side, head-to-tail, so that they couple male parts to female parts both at the same time. Some hermaphroditic snails also impregnate each other simultaneously. In neither case does one of the pair "act" as either male or female.
I don't know about this. However, does one individual lay eggs, or become pregnant or something similar? If so, I would suspect that there is more to the mating process than meets the eye (just speculation, you understand). Either way, I'd be perversely interested in knowing more about how worms do the business.
Cheers
r |
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Dave W.
Info Junkie
USA
26020 Posts |
Posted - 06/20/2005 : 09:28:42 [Permalink]
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quote:
Originally posted by latsot
I don't know about this. However, does one individual lay eggs, or become pregnant or something similar?
No, they both do.quote:
Either way, I'd be perversely interested in knowing more about how worms do the business.
This page includes a quick overview. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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latsot
Skeptic Friend
United Kingdom
70 Posts |
Posted - 06/21/2005 : 12:10:06 [Permalink]
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quote:
Originally posted by Dave W.
quote:
Originally posted by latsot
I don't know about this. However, does one individual lay eggs, or become pregnant or something similar?
No, they both do.quote:
Either way, I'd be perversely interested in knowing more about how worms do the business.
This page includes a quick overview.
Interesting. So I'd be even more interested to see evidence of sexual selection :-)
Cheers
r |
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