Dec 1, 2021 01:04 AM
It looks like Omicron causes milder illness – is this how COVID becomes endemic?
https://www.scivillage.com/thread-11354-...l#pid47601
Male animals are subject to stronger evolutionary pressures than females
https://elifesciences.org/for-the-press/...an-females
RELEASE: Male animals are subject to stronger selection pressures than females, which may allow populations to adapt to environmental change more efficiently, according to a report published in the open-access journal eLife.
The study supports one of the long-standing assumptions underpinning the idea that sexual selection bolsters adaptation: that stronger selection on males allows them to purge the population of genetic mutations that reduce survival fitness.
Sexual selection is selection arising from competition for mating partners and/or their reproductive cells (their eggs or sperm). For almost a century, researchers have thought that sexual selection is the ultimate selective force that generates the differences we see between male and female animals in terms of reproductive fitness and life history. Yet, little is known about how sexual selection combines with other environmental pressures to impact population demography and adaptive ability.
Living organisms accumulate mutations throughout life – some of which help them become fitter for survival, and some of which provide no benefit and may even cause a disadvantage (called deleterious mutations). Sexual selection is thought to promote evolutionary adaptation if it gives rise to stronger net selection – that is, the total purifying selection against deleterious mutations – in males rather than females. This is because a population’s productivity relies on females’ ability to reproduce, so that stronger net selection on males allows a population to get rid of the deleterious mutations quickly and adapt to their environment with a lower cost to the population, which may eventually reduce the risk of extinction.
“Our knowledge on whether such stronger sexual selection on males translates into stronger net selection to females is still limited,“ says first author Lennart Winkler, a PhD student at TU Dresden, Germany. “Previous studies have used the phenotypic variance of fitness to measure net selection, but its relevance has been questioned. An alternative measure is the organism’s genetic variance of fitness. We used both measures to show whether net selection is generally stronger on males across a broad range of species.”
The team ran a systematic literature search and compiled 101 paired estimates of male and female genetic variances across 26 species for two important components of an organism’s fitness: reproductive success and lifespan.
They then tested whether the phenotypic variances were aligned to the genetic variances, and whether genetic variances show consistent sex differences. They predicted that males would show larger genetic variance in reproductive success but not in lifespan.
They found that the phenotypic variance of lifespan but not of reproductive success predicted the genetic variance in either males or females. Importantly, however, the phenotypic variance of reproductive success was larger in males than females, and this translated into a male bias in genetic variance. This sex difference could be detected in polygamous but not monogamous species. By contrast, there were no consistent sex differences in phenotypic or genetic variance for lifespan.
“Our results have two major implications,” says senior author Tim Janicke, a researcher at the Centre d’Ecologie Fonctionnelle et Evolutive in Montpellier, France. “First, phenotypic variance of reproductive success is a poor predictor of purifying selection against deleterious mutations. Second, our findings provide support for the prediction that net selection is generally stronger on males compared to females, which may not only bolster local adaptation but can also reduce the risk of extinction when populations face challenging environmental conditions. Therefore, our results support the idea that sexual selection can play a pivotal role in evolutionary rescue.”
Ubiquitous food additive alters human microbiota and intestinal environment
https://news.gsu.edu/2021/11/30/ubiquito...vironment/
RELEASE: New clinical research indicates that a widely used food additive, carboxymethylcellulose, alters the intestinal environment of healthy persons, perturbing levels of beneficial bacteria and nutrients. These findings, published in Gastroenterology, demonstrate the need for further study of the long-term impacts of this food additive on health.
The research was led by a collaborative team of scientists from Georgia State University’s Institute for Biomedical Sciences, INSERM (France) and the University of Pennsylvania. Key contributions also came from researchers at Penn State University and Max Planck Institute (Germany).
Carboxymethylcellulose (CMC) is a synthetic member of a widely used class of food additives, termed emulsifiers, which are added to many processed foods to enhance texture and promote shelf life. CMC has not been extensively tested in humans but has been increasingly used in processed foods since the 1960s.
It had long been assumed that CMC was safe to ingest because it is eliminated in the feces without being absorbed. However, increasing appreciation of the health benefits provided by bacteria that normally live in the colon, and thus would interact with non-absorbed additives, has led scientists to challenge this assumption.
Experiments in mice found that CMC, and some other emulsifiers, altered gut bacteria resulting in more severe disease in a range of chronic inflammatory conditions, including colitis, metabolic syndrome and colon cancer. However, the extent to which such results are applicable to humans had not been previously investigated.
The team performed a randomized controlled-feeding study in healthy volunteers. Participants, housed at the study site, consumed an additive-free diet or an identical diet supplemented with carboxymethylcellulose (CMC). Because the diseases CMC promotes in mice take years to arise in humans, the researchers focused here on intestinal bacteria and metabolites.
They found that CMC consumption changed the make-up of bacteria populating the colon, reducing select species. Furthermore, fecal samples from CMC-treated participants displayed a stark depletion of beneficial metabolites that are thought to normally maintain a healthy colon.
Lastly, the researchers performed colonoscopies on subjects at the beginning and end of the study and noticed that a subset of subjects consuming CMC displayed gut bacteria encroaching into the mucus, which has previously been observed to be a feature of inflammatory bowel diseases and type 2 diabetes. Thus, while CMC consumption did not result in any disease per se in this two week study, collectively the results support the conclusions of animal studies that long-term consumption of this additive might promote chronic inflammatory diseases. Therefore, further studies of this additive are warranted.
“It certainly disproves the ‘it just passes through’ argument used to justify the lack of clinical study on additives,” said Georgia State University’s Dr. Andrew Gewirtz, one of the paper’s senior authors. Beyond supporting the need for further study of carboxymethylcellulose, the study “provides a general blueprint to carefully test individual food additives in humans in a well-controlled manner,” said co-senior author Dr. James Lewis, of the University of Pennsylvania, where the subjects were enrolled.
Lead author Dr. Benoit Chassaing, research director at INSERM, University of Paris, France, noted that such studies need to be large enough to account for a high degree of subject heterogeneity. “Indeed, our results suggest that responses to CMC and likely other food additives are highly personalized and we are now designing approaches to predict which individuals might be sensitive to specific additives,” Chassaing said.
https://www.scivillage.com/thread-11354-...l#pid47601
Male animals are subject to stronger evolutionary pressures than females
https://elifesciences.org/for-the-press/...an-females
RELEASE: Male animals are subject to stronger selection pressures than females, which may allow populations to adapt to environmental change more efficiently, according to a report published in the open-access journal eLife.
The study supports one of the long-standing assumptions underpinning the idea that sexual selection bolsters adaptation: that stronger selection on males allows them to purge the population of genetic mutations that reduce survival fitness.
Sexual selection is selection arising from competition for mating partners and/or their reproductive cells (their eggs or sperm). For almost a century, researchers have thought that sexual selection is the ultimate selective force that generates the differences we see between male and female animals in terms of reproductive fitness and life history. Yet, little is known about how sexual selection combines with other environmental pressures to impact population demography and adaptive ability.
Living organisms accumulate mutations throughout life – some of which help them become fitter for survival, and some of which provide no benefit and may even cause a disadvantage (called deleterious mutations). Sexual selection is thought to promote evolutionary adaptation if it gives rise to stronger net selection – that is, the total purifying selection against deleterious mutations – in males rather than females. This is because a population’s productivity relies on females’ ability to reproduce, so that stronger net selection on males allows a population to get rid of the deleterious mutations quickly and adapt to their environment with a lower cost to the population, which may eventually reduce the risk of extinction.
“Our knowledge on whether such stronger sexual selection on males translates into stronger net selection to females is still limited,“ says first author Lennart Winkler, a PhD student at TU Dresden, Germany. “Previous studies have used the phenotypic variance of fitness to measure net selection, but its relevance has been questioned. An alternative measure is the organism’s genetic variance of fitness. We used both measures to show whether net selection is generally stronger on males across a broad range of species.”
The team ran a systematic literature search and compiled 101 paired estimates of male and female genetic variances across 26 species for two important components of an organism’s fitness: reproductive success and lifespan.
They then tested whether the phenotypic variances were aligned to the genetic variances, and whether genetic variances show consistent sex differences. They predicted that males would show larger genetic variance in reproductive success but not in lifespan.
They found that the phenotypic variance of lifespan but not of reproductive success predicted the genetic variance in either males or females. Importantly, however, the phenotypic variance of reproductive success was larger in males than females, and this translated into a male bias in genetic variance. This sex difference could be detected in polygamous but not monogamous species. By contrast, there were no consistent sex differences in phenotypic or genetic variance for lifespan.
“Our results have two major implications,” says senior author Tim Janicke, a researcher at the Centre d’Ecologie Fonctionnelle et Evolutive in Montpellier, France. “First, phenotypic variance of reproductive success is a poor predictor of purifying selection against deleterious mutations. Second, our findings provide support for the prediction that net selection is generally stronger on males compared to females, which may not only bolster local adaptation but can also reduce the risk of extinction when populations face challenging environmental conditions. Therefore, our results support the idea that sexual selection can play a pivotal role in evolutionary rescue.”
Ubiquitous food additive alters human microbiota and intestinal environment
https://news.gsu.edu/2021/11/30/ubiquito...vironment/
RELEASE: New clinical research indicates that a widely used food additive, carboxymethylcellulose, alters the intestinal environment of healthy persons, perturbing levels of beneficial bacteria and nutrients. These findings, published in Gastroenterology, demonstrate the need for further study of the long-term impacts of this food additive on health.
The research was led by a collaborative team of scientists from Georgia State University’s Institute for Biomedical Sciences, INSERM (France) and the University of Pennsylvania. Key contributions also came from researchers at Penn State University and Max Planck Institute (Germany).
Carboxymethylcellulose (CMC) is a synthetic member of a widely used class of food additives, termed emulsifiers, which are added to many processed foods to enhance texture and promote shelf life. CMC has not been extensively tested in humans but has been increasingly used in processed foods since the 1960s.
It had long been assumed that CMC was safe to ingest because it is eliminated in the feces without being absorbed. However, increasing appreciation of the health benefits provided by bacteria that normally live in the colon, and thus would interact with non-absorbed additives, has led scientists to challenge this assumption.
Experiments in mice found that CMC, and some other emulsifiers, altered gut bacteria resulting in more severe disease in a range of chronic inflammatory conditions, including colitis, metabolic syndrome and colon cancer. However, the extent to which such results are applicable to humans had not been previously investigated.
The team performed a randomized controlled-feeding study in healthy volunteers. Participants, housed at the study site, consumed an additive-free diet or an identical diet supplemented with carboxymethylcellulose (CMC). Because the diseases CMC promotes in mice take years to arise in humans, the researchers focused here on intestinal bacteria and metabolites.
They found that CMC consumption changed the make-up of bacteria populating the colon, reducing select species. Furthermore, fecal samples from CMC-treated participants displayed a stark depletion of beneficial metabolites that are thought to normally maintain a healthy colon.
Lastly, the researchers performed colonoscopies on subjects at the beginning and end of the study and noticed that a subset of subjects consuming CMC displayed gut bacteria encroaching into the mucus, which has previously been observed to be a feature of inflammatory bowel diseases and type 2 diabetes. Thus, while CMC consumption did not result in any disease per se in this two week study, collectively the results support the conclusions of animal studies that long-term consumption of this additive might promote chronic inflammatory diseases. Therefore, further studies of this additive are warranted.
“It certainly disproves the ‘it just passes through’ argument used to justify the lack of clinical study on additives,” said Georgia State University’s Dr. Andrew Gewirtz, one of the paper’s senior authors. Beyond supporting the need for further study of carboxymethylcellulose, the study “provides a general blueprint to carefully test individual food additives in humans in a well-controlled manner,” said co-senior author Dr. James Lewis, of the University of Pennsylvania, where the subjects were enrolled.
Lead author Dr. Benoit Chassaing, research director at INSERM, University of Paris, France, noted that such studies need to be large enough to account for a high degree of subject heterogeneity. “Indeed, our results suggest that responses to CMC and likely other food additives are highly personalized and we are now designing approaches to predict which individuals might be sensitive to specific additives,” Chassaing said.