Friday, November 29, 2013 5:18:10 AM
Sex-starved fruit flies live shorter, more stressful lives
Male flies who expected sex had dramatically shortened lives
Neuropeptide F (red) levels increased in the brain when flies were tempted but not able to mate
By Melissa Hogenboom
Science reporter, BBC News
28 November 2013 Last updated at 14:00 ET
Sexual frustration impairs the health of fruit flies and causes premature death, according to new research.
Scientists found that male flies who were stimulated to mate but prevented from doing so, had their lives cut short by up to 40%.
Those allowed to copulate not only lived longer but suffered less stress.
The research is published in the Journal Science [ http://dx.doi.org/10.1126/science.1243339 ].
In the experiment, the flies were put in close proximity to genetically modified males who had been altered to release female sex pheromones.
These hormones are used by flies to judge whether a potential mate is nearby, so when males secreted this sexually charged scent, it instantly aroused other males.
But crucially, they were not able to mate.
The flies that were tantalised but denied any action showed more stress, a decrease in their fat-stores and had their lives cut short dramatically.
"We immediately observed that they looked quite sick very soon in the presence of these effeminised males," explained Dr Scott Pletcher at the University of Michigan, US, co-author of the research.
The common fruit fly has a very short life of about 60 days. This makes them an ideal organism to study aging as the genes that regulate a fly's lifespan have been found to closely parallel those in humans.
The team were interested in the neurons involved in aging. A brain chemical called neuropeptide F (NPF) - which has previously been linked to reward - was found to be instrumental.
When flies were exposed to an excess of female pheromones but had no opportunity to mate, their NPF levels increased.
Mating would usually regulate the neuropeptide to normal levels but when it stayed high, it caused the detrimental physiological consequences.
Costly act
The mere act of reproduction normally reduces a fly's life by about 10-15%, but the amount that their life was cut short in this study was unexpected.
"In that context mating can be quite beneficial, which is contrary to dogma. It suggests that the brain is somehow balancing this information about the environment through sensory input," Dr Pletcher told BBC News.
"Evolutionarily we hypothesise the animals are making a bet to determine that mating will happen soon.
"Those that correctly predict may be in a better position, they either produce more sperm or devote more energy to reproduction in expectation, and this may have some consequences [if they do not mate]," Dr Pletcher added.
Female power
Timothy Weil, lecturer at the University of Cambridge zoology department who was not involved with the study, said the work suggested that less successful males could lose out in the race to pass on their genes.
"Sex and food are the biggest drivers of animal behaviour and the female fly here seems to have the power. It could be a way for females to select for the best mates as the males who are not mating as much have negative health effects," he said.
"The work suggests that acting upon these physiological changes is important for the health of the animal," Dr Weil added.
In a separate study on roundworms, also published in Science, a team found that the presence of male pheromones reduced a female's lifespan.
Dr Pletcher said this parallel finding was encouraging because worms and flies have similar pathways, "which have so far been held up in mice and likely in primates too".
*
Related Stories
How to rear genetically modified flies Watch 20 NOVEMBER 2013, SCIENCE & ENVIRONMENT
http://www.bbc.co.uk/news/science-environment-24958489
Sex-starved flies 'turn to drink' 15 MARCH 2012, SCIENCE & ENVIRONMENT
http://www.bbc.co.uk/news/science-environment-17357560
Mutant flies that tell us about human diseases 22 MARCH 2012, SCIENCE & ENVIRONMENT
http://www.bbc.co.uk/news/science-environment-17398951
Fly's sexy song turns on immunity 05 OCTOBER 2011, NEWS
http://www.bbc.co.uk/nature/15170078
Flies get 'mind-control sex swap' 18 APRIL 2008, SCI/TECH
http://www.bbc.co.uk/2/hi/science/nature/7350403.stm
Related Internet links
Scott Pletcher at the University of Michigan
https://www.physiology.med.umich.edu/research/profiles/pletcher.htm
Timothy Weil at the University of Cambridge
http://www.zoo.cam.ac.uk/directory/dr-timothy-weil
*
BBC © 2013
http://www.bbc.co.uk/news/science-environment-25120980
--
Scent of Opposite Sex Shortens Lives of Flies and Worms
A female fruit fly. Pheromone-producing cells are labelled with a glowing green molecule.
Credit: Christi Gendron
by Ed Yong
November 28, 2013
Smells change us. Inhale the vapours of an apple pie or a bacon sandwich, and your body immediately starts getting ready for an incoming meal. You salivate. You start to produce more digestive enzymes. Your bloodstream courses with insulin, preparing your organs to absorb the nutrients that you’re about to consume.
But smells can have even more profound effects. Two teams of scientists have found that in worms and flies, the scent of pheromones from the opposite sex can speed up an individual’s ageing process and shorten its life. This happens even if no one has any sex.
Just by being around, one worm or fly can control the ageing process in another, at a distance.
While studying the nematode worm Caenorhabditis elegans, Anne Brunet’s team [ http://www.stanford.edu/group/brunet/lab%20members.html ] from Stanford University noticed that males seemed to shorten the lives of the opposite sex (hermaphrodites, whose bodies are female but who make both eggs and sperm).
Other scientists had noticed the same effect 17 years earlier [ http://www.ncbi.nlm.nih.gov/pubmed/8602217 ], but they assumed that it was due to the “stress of copulation”. But Brunet’s postdoc Travis Maures found that sterile hermaphrodites still suffered in the presence of males… and even in their absence! When he added hermaphrodites to containers that had previously housed males, they still aged more quickly. Their movements slowed, their bodies deteriorated, and their lifespans shortened by some 20 percent.
The males must be secreting some type of pheromone that stays in their environment and curtails the lives of the opposite sex. The team proved this by showing that mutant males which don’t produce pheromones don’t kill their mates early, while mutant hermaphrodites that can’t sense pheromones are immune to the males’ life-shortening powers.
Meanwhile, Scott Pletcher from the University of Michigan found similar patterns in fruit flies. In 2007, his team showed that the mere smell of food can influence the lifespan of flies [ https://www.sciencemag.org/content/315/5815/1133.short ]. Now they’ve found that sex pheromones can do the same.
The problem with fruit flies is that their sperm is toxic and every sexual encounter shortens the lives of females. To work out what the pheromones are doing, the team needed to somehow expose the flies to these smells without actually allowing them to mate. They did it through a clever genetic trick. A single gene called tra determines whether a fly produces male or female pheromones. By switching it on or off, postdocs Christi Gendron and Tsung-Han Kuo engineered male flies that smell like females, and vice versa.
Using these smell-swapped flies, they found that male flies store less fat, become easier to starve, age faster, and die quicker after detecting the scent of female. (The same thing happens to females that smell male pheromones, but to a less dramatic extent.)
“Initially, we thought that the males were just courting a lot or becoming more active, which wouldn’t be that interesting,” says Pletcher. But after carefully watching the flies, his team discounted these explanations. Instead, they showed that the ageing effect is driven by a few taste-sensitive neurons in the flies’ first pair of legs. When they disabled these neurons or just amputated the legs, the males became immune to the female pheromones.
The team also found a way of reversing this life-shortening effect—conjugal visits. If the males were actually allowed to have sex, their lifespans bounced back. That surprised Pletcher, who notes that people have long viewed reproduction and ageing as opposites. “The more energy you put towards reproduction, the less you have remaining to support your health,” he says. “But in this context, reproduction was actually beneficial.”
Why do these pheromones speed up the ageing process? Neither team knows, but both have some ideas. Pletcher speculates that it may be due to the trade-off between sex and longevity. Insulin, for example, is a hormone that’s best known for its role in controlling sugar levels in our blood, but it’s also involved in ageing. “If you reduce insulin signalling, organisms are long-lived but turn off reproduction,” says Pletcher. Pheromones may boost levels of insulin to get flies ready for sex, “and that might lead to enhanced ageing for reasons we don’t understand yet”.
He also suspects that the clash between expectations and experience is important. If we smell food and can’t eat any, the build-up of digestive enzymes can actually cause us harm. Likewise, male flies that smell females but can’t actually mate may suffer the consequences for their unfulfilled expectations. “They make this bet that they’re going to be reproducing soon, and they engage some physiological changes, like producing hormones.” If there’s no sex, these changes are harmful.
Brunet has a different hypothesis. “This is wild speculation,” she says, “but it may be due to sexual conflict.” By shortening the lives of their partners, males could ensure that their offspring aren’t facing competition from their mothers, while also reducing the mating opportunities available to other males. “That’s something we hadn’t considered,” says Pletcher. “It doesn’t entirely fit with our data because when males mate, some of those negative consequences go away, but maybe that means they are battling back?”
These quirky effects are fascinating in their own right, but it’s unclear if they have any relevance to us or to other mammals. “The jury’s out,” says Pletcher, “but I’m as optimistic as I’ve ever been that this would apply to mice, or even humans.” He’s particularly encouraged that both his team and Brunet’s have found similar phenomena in worms and flies—species that have been separated by over 900 million years of evolution. “Historically, genes and pathways of ageing that have been identified in worms and flies have also been relevant to mice.”
Brunet is more circumspect. “We joke that we should open a fragrance company, with fine-print warning labels that say, Caution: this might cause the premature demise of your mate,” she says. More seriously, she notes that it’s not clear what part pheromones play in sexual communication in humans. Mice clearly do use pheromones for this purpose, so the next step would be to see if mice can influence the pace of ageing in the opposite sex, without ever actually mating. “The experiments could be done, but they’re tricky,” she says.
*
Reference:
Gendron, Kuo, Harvanek, Chung, Yew, Dierick & Pletcher. 2013. Drosophila Life Span and Physiology Are Modulated by Sexual Perception and Reward. Science http://dx.doi.org/10.1126/science.1243339
Maures, Booth, Benayoun, Izrayelit, Schroeder & Brunet. 2013. Males Shorten the Life Span of C. elegans Hermaphrodites via Secreted Compounds. Science http://dx.doi.org/10.1126/science.1244160
*
More on ageing:
Almond-Sized Brain Region is Control Centre for Ageing
http://phenomena.nationalgeographic.com/2013/05/01/almond-sized-brain-region-is-control-centre-for-ageing/
Balancing amino acids for a longer life
http://phenomena.nationalgeographic.com/2009/12/02/balancing-amino-acids-for-a-longer-life/
Extending healthy life by getting rid of retired cells
http://phenomena.nationalgeographic.com/2011/11/02/extending-healthy-life-by-getting-rid-of-retired-cells/
Neurons Could Outlive the Bodies That Contain Them
http://phenomena.nationalgeographic.com/2013/02/25/neurons-could-outlive-the-bodies-that-contain-them/
Rapamycin – the Easter Island drug that extends lifespan of old mice
http://phenomena.nationalgeographic.com/2009/07/08/rapamycin-the-easter-island-drug-that-extends-lifespan-of-old-mice/
Secrets of the supercentenarians: Life begins at 100
http://phenomena.nationalgeographic.com/2009/09/05/secrets-of-the-supercentenarians-life-begins-at-100/
*
© 2013 National Geographic Society (emphasis in original)
http://phenomena.nationalgeographic.com/2013/11/28/scent-of-opposite-sex-shortens-lives-of-flies-and-worms/ [no comments yet]
Male flies who expected sex had dramatically shortened lives
Neuropeptide F (red) levels increased in the brain when flies were tempted but not able to mate
By Melissa Hogenboom
Science reporter, BBC News
28 November 2013 Last updated at 14:00 ET
Sexual frustration impairs the health of fruit flies and causes premature death, according to new research.
Scientists found that male flies who were stimulated to mate but prevented from doing so, had their lives cut short by up to 40%.
Those allowed to copulate not only lived longer but suffered less stress.
The research is published in the Journal Science [ http://dx.doi.org/10.1126/science.1243339 ].
In the experiment, the flies were put in close proximity to genetically modified males who had been altered to release female sex pheromones.
These hormones are used by flies to judge whether a potential mate is nearby, so when males secreted this sexually charged scent, it instantly aroused other males.
But crucially, they were not able to mate.
The flies that were tantalised but denied any action showed more stress, a decrease in their fat-stores and had their lives cut short dramatically.
"We immediately observed that they looked quite sick very soon in the presence of these effeminised males," explained Dr Scott Pletcher at the University of Michigan, US, co-author of the research.
The common fruit fly has a very short life of about 60 days. This makes them an ideal organism to study aging as the genes that regulate a fly's lifespan have been found to closely parallel those in humans.
The team were interested in the neurons involved in aging. A brain chemical called neuropeptide F (NPF) - which has previously been linked to reward - was found to be instrumental.
When flies were exposed to an excess of female pheromones but had no opportunity to mate, their NPF levels increased.
Mating would usually regulate the neuropeptide to normal levels but when it stayed high, it caused the detrimental physiological consequences.
Costly act
The mere act of reproduction normally reduces a fly's life by about 10-15%, but the amount that their life was cut short in this study was unexpected.
"In that context mating can be quite beneficial, which is contrary to dogma. It suggests that the brain is somehow balancing this information about the environment through sensory input," Dr Pletcher told BBC News.
"Evolutionarily we hypothesise the animals are making a bet to determine that mating will happen soon.
"Those that correctly predict may be in a better position, they either produce more sperm or devote more energy to reproduction in expectation, and this may have some consequences [if they do not mate]," Dr Pletcher added.
Female power
Timothy Weil, lecturer at the University of Cambridge zoology department who was not involved with the study, said the work suggested that less successful males could lose out in the race to pass on their genes.
"Sex and food are the biggest drivers of animal behaviour and the female fly here seems to have the power. It could be a way for females to select for the best mates as the males who are not mating as much have negative health effects," he said.
"The work suggests that acting upon these physiological changes is important for the health of the animal," Dr Weil added.
In a separate study on roundworms, also published in Science, a team found that the presence of male pheromones reduced a female's lifespan.
Dr Pletcher said this parallel finding was encouraging because worms and flies have similar pathways, "which have so far been held up in mice and likely in primates too".
*
Related Stories
How to rear genetically modified flies Watch 20 NOVEMBER 2013, SCIENCE & ENVIRONMENT
http://www.bbc.co.uk/news/science-environment-24958489
Sex-starved flies 'turn to drink' 15 MARCH 2012, SCIENCE & ENVIRONMENT
http://www.bbc.co.uk/news/science-environment-17357560
Mutant flies that tell us about human diseases 22 MARCH 2012, SCIENCE & ENVIRONMENT
http://www.bbc.co.uk/news/science-environment-17398951
Fly's sexy song turns on immunity 05 OCTOBER 2011, NEWS
http://www.bbc.co.uk/nature/15170078
Flies get 'mind-control sex swap' 18 APRIL 2008, SCI/TECH
http://www.bbc.co.uk/2/hi/science/nature/7350403.stm
Related Internet links
Scott Pletcher at the University of Michigan
https://www.physiology.med.umich.edu/research/profiles/pletcher.htm
Timothy Weil at the University of Cambridge
http://www.zoo.cam.ac.uk/directory/dr-timothy-weil
*
BBC © 2013
http://www.bbc.co.uk/news/science-environment-25120980
--
Scent of Opposite Sex Shortens Lives of Flies and Worms
A female fruit fly. Pheromone-producing cells are labelled with a glowing green molecule.
Credit: Christi Gendron
by Ed Yong
November 28, 2013
Smells change us. Inhale the vapours of an apple pie or a bacon sandwich, and your body immediately starts getting ready for an incoming meal. You salivate. You start to produce more digestive enzymes. Your bloodstream courses with insulin, preparing your organs to absorb the nutrients that you’re about to consume.
But smells can have even more profound effects. Two teams of scientists have found that in worms and flies, the scent of pheromones from the opposite sex can speed up an individual’s ageing process and shorten its life. This happens even if no one has any sex.
Just by being around, one worm or fly can control the ageing process in another, at a distance.
While studying the nematode worm Caenorhabditis elegans, Anne Brunet’s team [ http://www.stanford.edu/group/brunet/lab%20members.html ] from Stanford University noticed that males seemed to shorten the lives of the opposite sex (hermaphrodites, whose bodies are female but who make both eggs and sperm).
Other scientists had noticed the same effect 17 years earlier [ http://www.ncbi.nlm.nih.gov/pubmed/8602217 ], but they assumed that it was due to the “stress of copulation”. But Brunet’s postdoc Travis Maures found that sterile hermaphrodites still suffered in the presence of males… and even in their absence! When he added hermaphrodites to containers that had previously housed males, they still aged more quickly. Their movements slowed, their bodies deteriorated, and their lifespans shortened by some 20 percent.
The males must be secreting some type of pheromone that stays in their environment and curtails the lives of the opposite sex. The team proved this by showing that mutant males which don’t produce pheromones don’t kill their mates early, while mutant hermaphrodites that can’t sense pheromones are immune to the males’ life-shortening powers.
Meanwhile, Scott Pletcher from the University of Michigan found similar patterns in fruit flies. In 2007, his team showed that the mere smell of food can influence the lifespan of flies [ https://www.sciencemag.org/content/315/5815/1133.short ]. Now they’ve found that sex pheromones can do the same.
The problem with fruit flies is that their sperm is toxic and every sexual encounter shortens the lives of females. To work out what the pheromones are doing, the team needed to somehow expose the flies to these smells without actually allowing them to mate. They did it through a clever genetic trick. A single gene called tra determines whether a fly produces male or female pheromones. By switching it on or off, postdocs Christi Gendron and Tsung-Han Kuo engineered male flies that smell like females, and vice versa.
Using these smell-swapped flies, they found that male flies store less fat, become easier to starve, age faster, and die quicker after detecting the scent of female. (The same thing happens to females that smell male pheromones, but to a less dramatic extent.)
“Initially, we thought that the males were just courting a lot or becoming more active, which wouldn’t be that interesting,” says Pletcher. But after carefully watching the flies, his team discounted these explanations. Instead, they showed that the ageing effect is driven by a few taste-sensitive neurons in the flies’ first pair of legs. When they disabled these neurons or just amputated the legs, the males became immune to the female pheromones.
The team also found a way of reversing this life-shortening effect—conjugal visits. If the males were actually allowed to have sex, their lifespans bounced back. That surprised Pletcher, who notes that people have long viewed reproduction and ageing as opposites. “The more energy you put towards reproduction, the less you have remaining to support your health,” he says. “But in this context, reproduction was actually beneficial.”
Why do these pheromones speed up the ageing process? Neither team knows, but both have some ideas. Pletcher speculates that it may be due to the trade-off between sex and longevity. Insulin, for example, is a hormone that’s best known for its role in controlling sugar levels in our blood, but it’s also involved in ageing. “If you reduce insulin signalling, organisms are long-lived but turn off reproduction,” says Pletcher. Pheromones may boost levels of insulin to get flies ready for sex, “and that might lead to enhanced ageing for reasons we don’t understand yet”.
He also suspects that the clash between expectations and experience is important. If we smell food and can’t eat any, the build-up of digestive enzymes can actually cause us harm. Likewise, male flies that smell females but can’t actually mate may suffer the consequences for their unfulfilled expectations. “They make this bet that they’re going to be reproducing soon, and they engage some physiological changes, like producing hormones.” If there’s no sex, these changes are harmful.
Brunet has a different hypothesis. “This is wild speculation,” she says, “but it may be due to sexual conflict.” By shortening the lives of their partners, males could ensure that their offspring aren’t facing competition from their mothers, while also reducing the mating opportunities available to other males. “That’s something we hadn’t considered,” says Pletcher. “It doesn’t entirely fit with our data because when males mate, some of those negative consequences go away, but maybe that means they are battling back?”
These quirky effects are fascinating in their own right, but it’s unclear if they have any relevance to us or to other mammals. “The jury’s out,” says Pletcher, “but I’m as optimistic as I’ve ever been that this would apply to mice, or even humans.” He’s particularly encouraged that both his team and Brunet’s have found similar phenomena in worms and flies—species that have been separated by over 900 million years of evolution. “Historically, genes and pathways of ageing that have been identified in worms and flies have also been relevant to mice.”
Brunet is more circumspect. “We joke that we should open a fragrance company, with fine-print warning labels that say, Caution: this might cause the premature demise of your mate,” she says. More seriously, she notes that it’s not clear what part pheromones play in sexual communication in humans. Mice clearly do use pheromones for this purpose, so the next step would be to see if mice can influence the pace of ageing in the opposite sex, without ever actually mating. “The experiments could be done, but they’re tricky,” she says.
*
Reference:
Gendron, Kuo, Harvanek, Chung, Yew, Dierick & Pletcher. 2013. Drosophila Life Span and Physiology Are Modulated by Sexual Perception and Reward. Science http://dx.doi.org/10.1126/science.1243339
Maures, Booth, Benayoun, Izrayelit, Schroeder & Brunet. 2013. Males Shorten the Life Span of C. elegans Hermaphrodites via Secreted Compounds. Science http://dx.doi.org/10.1126/science.1244160
*
More on ageing:
Almond-Sized Brain Region is Control Centre for Ageing
http://phenomena.nationalgeographic.com/2013/05/01/almond-sized-brain-region-is-control-centre-for-ageing/
Balancing amino acids for a longer life
http://phenomena.nationalgeographic.com/2009/12/02/balancing-amino-acids-for-a-longer-life/
Extending healthy life by getting rid of retired cells
http://phenomena.nationalgeographic.com/2011/11/02/extending-healthy-life-by-getting-rid-of-retired-cells/
Neurons Could Outlive the Bodies That Contain Them
http://phenomena.nationalgeographic.com/2013/02/25/neurons-could-outlive-the-bodies-that-contain-them/
Rapamycin – the Easter Island drug that extends lifespan of old mice
http://phenomena.nationalgeographic.com/2009/07/08/rapamycin-the-easter-island-drug-that-extends-lifespan-of-old-mice/
Secrets of the supercentenarians: Life begins at 100
http://phenomena.nationalgeographic.com/2009/09/05/secrets-of-the-supercentenarians-life-begins-at-100/
*
© 2013 National Geographic Society (emphasis in original)
http://phenomena.nationalgeographic.com/2013/11/28/scent-of-opposite-sex-shortens-lives-of-flies-and-worms/ [no comments yet]
Greensburg, KS - 5/4/07
"Eternal vigilance is the price of Liberty."
from John Philpot Curran, Speech
upon the Right of Election, 1790
F6
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