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Author | Topic: The limitations of Sexual Selection | |||||||||||||||||||
aiki Member (Idle past 4292 days) Posts: 43 Joined: |
In birds where the male is expected to feed the incubating female and later on the chicks, he can demonstrate his provider skills to the female with courtship feeding. He finds and offers food to the female, feeding her in the same way he would a begging chick. The extra food supplies also help bring her into breeding condition.
With species that share parenting equally, courtship often involves both members of the pair demonstrating a ritualised version of some aspect of parenting skills. For example, in Great Crested Grebes the courtship display is a synchronised dance in which both birds dive, tread water and offer pondweed (a nesting material) to each other. In many birds of prey the courtship involves elaborate aerobatics, with mid-air food passes (showing skill as a provider) and chases with talon-grappling (demonstrating ability to defend the territory from intruders).
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Dr Adequate Member (Idle past 284 days) Posts: 16113 Joined: |
In birds where the male is expected to feed the incubating female and later on the chicks, he can demonstrate his provider skills to the female with courtship feeding. He finds and offers food to the female, feeding her in the same way he would a begging chick. The extra food supplies also help bring her into breeding condition. Interesting. Now besides being a display of competence, this is also an insurance of future behavior. It is true that courtship feeding doesn't in itself prove that he'll care for her and her chick after he's knocked her up, rather than running after another female --- but in order to successfully pursue another female, he'd have to expend the same courtship effort on female no. 2. So this female strategy tilts the cost-benefit calculation in favor of good providers and against philanderers. And it's another ESS --- no individual can gain by bucking the system once it's in place.
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aiki Member (Idle past 4292 days) Posts: 43 Joined: |
With birds in which the chicks are helpless and confined to the nest for weeks after hatching (altricial), they need sheltering, defending from predators, frequent feeding and their droppings taken away. It's a two-bird job, so if a male shags and immediately leaves to court another female, there's pretty much zero chance that any chicks he fathers will survive. However, sneaky extra-pair copulations between birds of neighbouring territories are VERY common among some of these supposedly 'monogamous' species.
You see obvious sexual dimorphism more often in species with precocial chicks, able to run about and feed themselves soon after hatching (eg ducks, chickens). The female (or in a few cases the male - eg in phalaropes and Dotterels the male does all the parental care) doesn't need a second helper so can select a mate solely on the basis of looks and vigour. Edited by aiki, : clarify some bits
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fearandloathing Member (Idle past 4145 days) Posts: 990 From: Burlington, NC, USA Joined: |
Hi Slevesque,
I just got done reading about quiet crickets. On the island of Kauai in Hawaii there is a population of crickets that are undergoing rapid change it seems for several reasons, predation and a population bottleneck.
quote: quote: I thought i would share this as it seems to be a perfect example of the the "guppy experiment" taking place in the real world. Pressure from a population bottleneck and predation have caused a rapid change in this group of crickets. I guess one of the questions is whether this change is due to the predation or the bottleneck. I would suspect it is both. Edited by fearandloathing, : No reason given. Edited by fearandloathing, : No reason given. "I hate to advocate the use of drugs, alcohol, violence, or insanity to anyone, but they always worked for me." - Hunter S. Thompson Ad astra per aspera Nihil curo de ista tua stulta superstitione.
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anglagard Member (Idle past 836 days) Posts: 2339 From: Socorro, New Mexico USA Joined: |
Percy writes: The recent discussion prompts me to ask whether in species where males help raise the young, do we know whether drabness in males is more common? A drab male would be more likely to be around to help, so females might develop a greater preference (tolerance?) for drab males. This appears to largely be the case among the Cichlid family of fishes, at least those in the wild. From the Wiki on Cichlids.
quote: Generally same size, same drab look (until artificially selected for bright colors by human breeders). {ABE} There are many counterexamples however, it is a big family{/ABE} Another quote from the same article may prove of interest to this crowd.
quote: Edited by anglagard, : No reason given. The idea of the sacred is quite simply one of the most conservative notions in any culture, because it seeks to turn other ideas - uncertainty, progress, change - into crimes. Salman Rushdie This rudderless world is not shaped by vague metaphysical forces. It is not God who kills the children. Not fate that butchers them or destiny that feeds them to the dogs. It’s us. Only us. - the character Rorschach in Watchmen
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Dr Adequate Member (Idle past 284 days) Posts: 16113 Joined: |
I am positing that it does have a limiting affect because the preferences of the females is itself a selectable trait. Females who have preferences for characteristics who diminish fitness (bright colors) will have offsprings who will be at a disadvantage compared to offsprings of those who have preferences for less noticeable characteristics. I've been thinking about this, and I did some computer simulations, and you turn out to be wrong. You have in mind a situation where the female ideal of male beauty is itself a variable trait; for example the males vary in tail length (let's say) and the females vary in how long they like male tails (and perhaps also in how picky they are about this). This differs from my idea of how it usually works, in which all females would in principle prefer an infinitely long tail, but let's look at your hypothesis and see what would happen. Now, consider that for any given female preferences, there is an optimum point at which males best satisfy the combined demands of natural and sexual selection; at any given time we expect the average value of the male trait to be close to this moving target because of the selective pressures (but not usually dead on it because of genetic drift). Now, consider the case where the males tend to have the male trait to a degree that is (even slightly) below the optimum. Then females with a preference for greater values of the male trait have a selective advantage, because they will have a greater tendency to choose males closer to the optimum, which will therefore have a higher net fitness, which will be inherited by her children. Similarly, when males tend to have the male trait in excess of the optimum, females with a preference for smaller values of the male trait will be favored.
That is the selective pressure on female preference. It has nothing to do with what would be good for the species; it is driven by the drift of the values of the male traits around the optimum; that is, on a random factor. (Of course, female preference is also subject to genetic drift, which is another random factor.) Computer simulations bear this out. Selective pressures keep the male trait near the ever-shifting optimum; meanwhile female preference goes on what looks for all the world like a random walk; and if there is any bias in the randomness, it certainly does not seem to be in the direction of eliminating the male trait and female preference. Edited by Dr Adequate, : No reason given.
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