Population benefits of sexual selection explain the existence of males

May 18, 2015
Biologists have long puzzled over why males are necessary for reproduction. New research, published in the journal Nature, reveals that an evolutionary force known as 'sexual selection' improves population genetic health and protects against extinction. Credit: University of East Anglia

New research from the University of East Anglia shows that an evolutionary force known as 'sexual selection' can explain the persistence of sex as a dominant mechanism for reproducing offspring.

Biologists have long puzzled about how evolutionary selection, known for its ruthless requirement for efficiency, allows the existence of males - when in so many species their only contribution to reproduction are spermatozoa.

But research published today in Nature shows that sexual selection - when males compete and females choose over reproduction - improves population health and protects against extinction, even in the face of genetic stress from high levels of inbreeding.

The findings help explain why sex persists as a dominant mechanism for reproducing offspring.

Lead researcher Prof Matt Gage, from UEA's School of Biological Sciences, said: "Sexual selection was Darwin's second great idea, explaining the evolution of a fascinating array of sights, sounds and smells that help in the struggle to reproduce - sometimes at the expense of survival.

"Sexual selection operates when males compete for reproduction and females choose, and the existence of two different sexes encourages these processes. It ultimately dictates who gets to reproduce their genes into the next generation - so it's a widespread and very powerful evolutionary force.

"Almost all multicellular species on earth reproduce using sex, but its existence isn't easy to explain because sex carries big burdens, the most obvious of which is that only half of your offspring - daughters - will actually produce offspring. Why should any species waste all that effort on sons?

"We wanted to understand how Darwinian selection can allow this widespread and seemingly wasteful reproductive system to persist, when a system where all individuals produce offspring without sex - as in all-female asexual populations - would be a far more effective route to reproduce greater numbers of offspring.

Biologists have long puzzled over why males are necessary for reproduction. New research, published in the journal Nature, reveals that an evolutionary force known as 'sexual selection' improves population genetic health and protects against extinction. To uncover this role of sexual selection, the research team evolved Tribolium flour beetles over 10 years under controlled conditions in the laboratory. Credit: University of East Anglia

"Our research shows that competition among males for reproduction provides a really important benefit, because it improves the genetic health of populations. Sexual selection achieves this by acting as a filter to remove harmful genetic mutations, helping populations to flourish and avoid extinction in the long-term."

To uncover this role of sexual selection, the research team evolved Tribolium flour beetles over 10 years under controlled conditions in the laboratory, where the only difference between populations was the intensity of sexual selection during each adult reproductive stage.

The strength of sexual selection ranged from intense competition and choice where 90 males competed for reproduction with only 10 females, through to the complete absence of sexual selection, with only single males and females in monogamous pairings, where females got no choice and experienced no competition.

After seven years of reproduction under these conditions, representing about 50 generations, the study exposed the underlying genetic health of the resulting populations. The team used experimental inbreeding to reveal the relative amount of deleterious mutations that lay hidden in each population.

They found that populations that had previously experienced strong sexual selection maintained higher fitness and were resilient to extinction in the face of inbreeding - with some populations surviving even after 20 inbreeding generations where a brother was mated with a sister in each generation.

However populations that had experienced weak or non-existent sexual selection showed more rapid declines in health under inbreeding - and all went extinct by the 10th generation.

Credit: University of East Anglia

Prof Gage said: "These results show that sexual selection is important for population health and persistence, because it helps to purge negative and maintain positive genetic variation in a population.

"To be good at out-competing rivals and attracting partners in the struggle to reproduce, an individual has to be good at most things, so sexual selection provides an important and effective filter to maintain and improve population genetic health.

"Our findings provide direct support for the idea that sex persists as a dominant mode of because it allows sexual selection to provide these important genetic benefits.

"In the absence of sex, populations accumulate deleterious mutations through a ratcheting effect where each new mutation takes a population closer to extinction. Sexual selection helps to remove those mutations, enabling populations to persist against the threat of extinction.

"Our monogamous treatment, for example, where there was no for 50 generations, resulted in a lower level of and rapid extinction when populations were challenged by inbreeding. All the populations derived from monogamous histories became extinct after just eight generations.

"By contrast, populations derived from the same ancestors and identical apart from having the opportunity for male competition and female choice at each adult stage, maintained health and avoided extinction, with some family lines still reproducing happily even after 20 generations of inbreeding."

Explore further: Research finds clue to why females live longer than males

More information: 'Sexual selection protects against extinction' is published in the journal Nature on May 18. DOI: 10.1038/nature14419

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14 comments

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JRi
1 / 5 (2) May 18, 2015
I wonder if this applies to humans as well. The tribes where couples are faithful and truly monogamous, become genetically inferior over time, compared to those where members of the community cheat, or like in some other cultures, where one (alpha) male can have many wives.
Hidingfromyou
1 / 5 (2) May 18, 2015
To JRi: Yes, it would apply to all animals with sexes, b/c the evolution of males/females happened long before humans - and any extant species. However, the pressure of sexual selection varies between species.

However, these researchers are incorrect. Their research demonstrates the continued usefulness of males and sexual selection, not the original reason for the evolution of males.
dan42day
not rated yet May 18, 2015
sex carries big burdens, the most obvious of which is that only half of your offspring - daughters - will actually produce offspring. Why should any species waste all that effort on sons?


Perhaps, at least in many species, because a son can potentially pass the family genes along to many more offspring than a daughter?
jsdarkdestruction
5 / 5 (5) May 19, 2015
1. This is Anti young earth creationist. Why do you think your particular flavor of Christianity is supported and believed by all of the Christians in the world and represent your views and beliefs as theirs too? Many more disagree with you than agree.
2. You don't really want evidence presented and it explained to you and to look at it with an open mind. You are talking big but we don't buy it. Your beliefs are predetermined and unchangeable. You do your religion a great disservice here.
malapropism
5 / 5 (5) May 19, 2015
There is no mechanism to allow separation of the organisms to male and female.

Normally I deplore comments of the sort I'm going to make here and don't indulge in them but sometimes pragmatism overcomes scruples. You are a f*ing idiot. Ever heard of X and Y chromosomes?
Torbjorn_Larsson_OM
5 / 5 (5) May 19, 2015
I, for one, welcome my Sexual Over... um, wait.

@JRI: First, there isn't any selection on group level. Second, you don't get sexual selection if you think selection for more socialized individuals can't happen on a sexual basis. It probably did, as it helped form tool cultures - see how the only chimps discovered to hunt with spears are female chimps that are allowed to keep much of their prey, making spear hunting sustainable. Choosing mates that let you do hunting promotes tool use.

@HFY: You don't get sexual selection (or any other evolutionary selection) either, since you suppose it doesn't happen in small, survivable steps. A behavior can be promoted from small beginnings (see how our dead outer skin evolved in amphibians to allow terrestrial life) or co-opted (see how legs were co-opted in birds for wings).

And of course the insane creationist commentaries need no specific response. "Science. It works, bitches." [ https://xkcd.com/54/ ] Evolution tested, again!
jsdarkdestruction
5 / 5 (4) May 19, 2015
"God" "Jesus" "bible"
Those things don't have a place in science discussions.
Were you there when your gods son was nailed to the cross? What proof do you have other than books written after the people who are claimed to have written them were dead?

http://en.m.wikip...n_of_sex
Read this ren and it becomes much easier to understand. The info is out there You just ccan't let your religious beliefs blind you to it.

jsdarkdestruction
5 / 5 (3) May 20, 2015
Your source is a book of myths from 2000 years ago.
Did you read the entry I linked to? It has answers to your question if you just look.
AZWarrior
not rated yet May 25, 2015
Well duh. Evolution works though genetic variations. Not possible with asexual reproduction. We only have known this, like forever.
Captain Stumpy
4 / 5 (4) May 25, 2015
Not myths but real human history. Read to learn
most athiests know more about your bible than you do
it is made up history which is subjected to the same fallacious beginnings as any comic (modern myths) today and subjected to the same campaigns which make comics popular: peer pressure and ostracizing with ridicule of non-believers

historical data from multiple sources shows that the bible also stole myths for their own purpose, as well as blatantly cut out anything which would cause too much argument about legitimate "sacred" or holy beginnings (the Canon)

the bible is also proven to be fallacious on most counts of "historical" data as well, when compared with multiple sources (IOW- contrived and fallacious for population control or aggrandizement to justify being chosen separately and to justify genocide)
docile
May 25, 2015
This comment has been removed by a moderator.
zz5555
5 / 5 (2) May 25, 2015
Well duh. Evolution works though genetic variations. Not possible with asexual reproduction. We only have known this, like forever.

Are you saying that bacteria don't evolve? That seems like a surprising comment to make. Especially given that bacteria have been shown to evolve to become drug resistant.
viko_mx
1 / 5 (2) May 25, 2015
"Well duh. Evolution works though genetic variations. Not possible with asexual reproduction. We only have known this, like forever."

Not evolution work with genetic variation but embbeded mechanisms for recombination of genetic information between male and female organisms or between different single cell organisms wich allow biodiversity in the frame of species. Every indivuidual have genes from both parents thanks to this mechanisms for recombinations and here the mutations is not needed. In fact the mutations are highly undesirable in all cases.
Captain Stumpy
5 / 5 (1) May 26, 2015
In fact the mutations are highly undesirable in all cases.
@viko
besides spouting off jk's dogma, you are totally wrong, as pointed out by zz5555 right above you

bacteria evolved and mutated the ability to become drug resistant
and we can SEE that happening as well: http://myxo.css.m...dex.html

in fact, Lenski alone is enough to destroy your argument... but even beyond that, it has been repeatedly VALIDATED through other experiments, like Dr. Extavour

even when the idiot jk tried to argue this point (while using Extavour to say her work supported his claims) Dr. Extavour stated he was not only WRONG, but also that her work supported Lenski's conclusions

that is how science works, and it is also why jk is continually being called a crackpot
one more reason: http://rspb.royal...full.pdf

science works
religion is only good for controlling the weak minded

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