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Author Topic:   The limitations of Sexual Selection
Member (Idle past 4371 days)
Posts: 43
Joined: 04-28-2010

Message 31 of 36 (620392)
06-16-2011 4:26 AM
Reply to: Message 29 by Dr Adequate
06-16-2011 1:32 AM

Re: A Sexual Selection Question
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).

This message is a reply to:
 Message 29 by Dr Adequate, posted 06-16-2011 1:32 AM Dr Adequate has replied

Replies to this message:
 Message 32 by Dr Adequate, posted 06-16-2011 7:45 AM aiki has replied

Dr Adequate
Member (Idle past 363 days)
Posts: 16113
Joined: 07-20-2006

Message 32 of 36 (620402)
06-16-2011 7:45 AM
Reply to: Message 31 by aiki
06-16-2011 4:26 AM

Re: A Sexual Selection Question
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.

This message is a reply to:
 Message 31 by aiki, posted 06-16-2011 4:26 AM aiki has replied

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 Message 33 by aiki, posted 06-16-2011 8:38 AM Dr Adequate has not replied

Member (Idle past 4371 days)
Posts: 43
Joined: 04-28-2010

Message 33 of 36 (620404)
06-16-2011 8:38 AM
Reply to: Message 32 by Dr Adequate
06-16-2011 7:45 AM

Re: A Sexual Selection Question
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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Member (Idle past 4223 days)
Posts: 990
From: Burlington, NC, USA
Joined: 02-24-2011

Message 34 of 36 (620706)
06-20-2011 9:56 AM
Reply to: Message 1 by slevesque
06-14-2011 2:23 PM

Quiet crickets
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.
Quick evolution leads to quiet crickets
December 2006, updates added June 2008 and June 2011
Attack of the flesh-eating parasitoid maggots!! Mutant mute crickets run rampant in tropical paradise!! The headlines may sound like a trailer for a cheap horror flick but in fact, these sensationalist sound bites accurately describe the situation on the Hawaiian island of Kauai. The "flesh-eating parasitoid maggots" are the offspring of the fly, Ormia ochracea, which invaded Hawaii from North America, and the mutant crickets are the flies' would-be victims. The flies follow the chirps of a calling cricket and then deposit a smattering of wriggling maggots onto the cricket's back. The maggots burrow into the cricket, and emerge, much fatter, a week later killing the cricket in the process. But this fall, biologists Marlene Zuk, John Rotenberry, and Robin Tinghitella announced a breakdown in business-as-usual in this gruesome interaction: in just a few years, the crickets of Kauai have evolved a strategy to avoid becoming a maggot's lunch but the strategy comes at a cost...
However crickets got to Hawaii, it's clear that there weren't very many of them when they arrived. The low level of genetic variation in Hawaiian populations today strongly suggests that these crickets have experienced a population bottleneck a reduction in population size, which probably occurred when small groups of crickets invaded a new island. This small starting population size could have contributed to the spread of the silent wing mutation today. When population size is small, selection may favor females that aren't very choosy about their mates. After all, when there are only a few males to choose from, a picky female may not mate at all! If this is the case if female crickets on Hawaii evolved to be less choosy early on, and as described in the news update above, it seems they did it would have made it easier for the silent wing mutation to spread through the population. Unfussy females would accept silent partners and pass the silent gene on to their offspring.
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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Member (Idle past 915 days)
Posts: 2339
From: Socorro, New Mexico USA
Joined: 03-18-2006

Message 35 of 36 (620793)
06-20-2011 8:09 PM
Reply to: Message 25 by Percy
06-15-2011 1:20 PM

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.
All species show some form of parental care for both eggs and larvae, often nurturing free-swimming young until they are weeks or months old.
Communal parental care, where multiple monogamous pairs care for a mixed school of young have also been observed in multiple cichlid species, including Amphilophus citrinellus, Etroplus suratensis, and Tilapia rendalli.[46][47][48] Comparably, the fry of Neolamprologus brichardi, a species that commonly lives in large groups, are protected not only by the adults, but also by older juveniles from previous spawns.[49]
Several cichlids, including discus (Symphysodon spp.), some Amphilophus species, Etroplus and Uaru species feed their young with a skin secretion from mucous glands.[4][50]
Parental care falls into one of four categories:[50] substrate or open brooders, secretive cave brooders (also known as guarding speleophils[51]), and at least two types of mouthbrooders, ovophile mouthbrooders and larvophile mouthbrooders.[52]
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.
Cichlids are particularly well known for having evolved rapidly into a large number of closely related but morphologically diverse species within large lakes, particularly Tanganyika, Victoria, Malawi, and Edward.[8][9] Their diversity in the African Great Lakes is important for the study of speciation in evolution.[10]
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

This message is a reply to:
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Dr Adequate
Member (Idle past 363 days)
Posts: 16113
Joined: 07-20-2006

Message 36 of 36 (620969)
06-22-2011 3:56 AM
Reply to: Message 7 by slevesque
06-15-2011 1:07 AM

Drift: Beyond The ESS
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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