Focusing on guppies, small fresh-water fish biologists have studied for long, the researchers found that guppies living in environments with a large number of predators have adapted to reproduce earlier in life than guppies from low-predation localities. Moreover, when reproduction ceases, guppies from high-predation localities are far older, on average, than guppies from low-predation localities, indicating that high-predation guppies enjoy a long “reproductive period” – the time between first and last reproduction.
“In earlier work, we showed that guppies from high predation environments have longer lifespans,” said David Reznick, professor of biology. “Our new study explores how and why this happens. We found that fish from populations enjoying longer lifespans live longer because there is a selective increase in their reproductive lifespan. Indeed, theory predicts this result because only reproductive lifespan determines fitness.”
Study results appear Dec. 27 in the online edition of the Public Library of
Science – Biology.
The study supports the controversial hypothesis that natural selection – the process in nature by which only organisms best adapted to their environment tend to survive and pass on their genetic characters in increasing numbers to succeeding generations – introduces changes in only a specific segment of an organism’s lifespan.
The researchers conducted their experiments by comparing life-history traits in 240 guppies they retrieved from high- and low-predation streams in mountains in Trinidad. In their analysis, they divided the life history into three non-overlapping segments: the age at maturity (birth to first reproduction), the reproductive lifespan (first to last reproduction) and the post-reproductive lifespan (last reproduction to death). They also devised a statistical criterion for evaluating whether or not guppies had a post-reproductive lifespan, that is, did guppies live significantly past the end of their capacity to reproduce?
“We were exploring whether or not fish have the equivalent of mammalian menopause,” Reznick said. “We found that 60 percent of the fish had a significant post-reproductive lifespan, indicating that, yes, fish do have menopause. Indeed, their patterns of growing old are similar to those of mammals.”
The researchers’ statistical analysis also showed that regardless of which environments the guppies lived in, there were no differences among their populations in the probability of having a post-reproductive lifespan or in its duration.
“This is just what one might predict because these fish provide no care for their young,” explained Reznick. “The older fish, after they stop reproducing, do not contribute to the fitness of young fish. As a result, the post-reproductive period is not influenced by natural selection. This result could be of interest to those who study menopause in humans and who have argued that post-reproductive humans can increase their own fitness by contributing to the fitness of their grandchildren and that the prolonged post-reproductive lifespan of humans is, therefore, the product of natural selection.
“But such arguments are difficult to prove by working on a single population or species. Nevertheless, our results show how it would be possible to evaluate whether or not menopause in humans has been shaped by natural selection. Appropriate comparisons, such as those between humans and apes, would help.”
Reznick was assisted in the study by Michael Bryant of the California Institute of the Arts and Donna Holmes of the University of Idaho. The Population Biology Division of the National Research Foundation provided support.
Source: University of California, Riverside
Related stories:
Scientists learn how food affects the brain
In addition to helping protect us from heart disease and cancer, a balanced diet and regular exercise can also protect the brain and ward off mental disorders.
Scientists use Iceland's genealogical database to pinpoint the heritage of a deadly disease
A collaboration of scientists from Iceland and the United States has used Iceland's genealogical database to trace the ancestors of patients suffering from hereditary cystatin C amyloid angiopathy (HCCAA). Analysis shows that the deadly mutation in the cystatin C gene, L68Q, derives from a common ancestor born roughly 18 generations ago, around 1550AD. Details are published June 20th in the open-access journal
PLoS Genetics.
Nitrogen retained through loss
The nitrogen cycle plays a major role in seagrass fields. Dutch researcher Arie Vonk studied the nitrogen dynamics of seagrasses in Indonesia. He discovered that the interaction between seagrasses, animals and microorganisms results in an efficient nitrogen cycle in tropical seagrass fields. Consequently the nitrogen lost from seagrasses is still retained.
Fluctuating diet increases risk of sudden death
New research has revealed that binge eating then dieting may significantly reduce lifespan.
Fish devastated by sex-changing chemicals in municipal wastewater
While most people understand the dangers of flushing toxic chemicals into the ecosystem through municipal sewer systems, one potentially devastating threat to wild fish populations comes from an unlikely source: estrogen.
The bear necessities of aging
According to George Bernard Shaw: “We don’t stop playing because we grow old; we grow old because we stop playing,” but how fast does that aging occur once started" In the case of populations of salmon in Alaska studied by Stephanie Carlson and colleagues at the University of Washington and McGill University and reported on in this week’s PLoS ONE, it all depends on how choosy are the bears which feed on them.
It's never too late to get it back! Aging interrupted
Much research has shown that reduced calorie intake can increase health and longevity. Professor Stephen Spindler (University of California) and his collaborators* have discovered that reducing calorie intake later in life can still induce many of the health and longevity benefits of life-long calorie reduction. Importantly, this also includes anti-cancer effects. They are using this knowledge to establish a novel screening technique to find drugs which mimic this longevity effect.
Single Molecule Makes Obese Mice Healthy
Researchers have used a single compound to increase the lifespan of obese mice, and found that the drug reversed nearly all of the changes in gene expression patterns found in mice on high calorie diets—some of which are associated with diabetes, heart disease, and other significant diseases related to obesity. The research, led by investigators at Harvard Medical School and the National Institute on Aging, is the first time that the small molecule resveratrol has been shown to offer survival benefits in a mammal. The study is reported in the November 1 advanced online edition of
Nature.
