Mating changes female behaviour across a wide range of animals, with these changes induced by components of the male ejaculate, such as sperm and seminal fluid proteins. However, males can vary significantly in their ejaculates, due to factors such as age, mating history, or feeding status. This male variation may therefore lead to variation in the strength of responses males can stimulate in females.
Using the fruit fly, Drosophila melanogaster, we tested whether age, mating history, and feeding status shape an important, but understudied, post-mating response – increased female-female aggression.
We found that females mated to old males fought less than females mated to young males. Females mated to old, sexually active males fought even less than those mated to males who were merely old, but there was no effect of male starvation status on mating-induced female aggression.
Male condition can therefore influence how females interact with each other – who you mate with changes your interactions with members of the same sex!
Could this happen in other species?
We know that other species (including humans!) have proteins in the seminal fluid that males transfer to females during sex. Various of these proteins have effects on female physiology and behaviour, but no one knows if these affect aggression (in humans or any other species).
We also know that male age (in flies and humans) results in reduced fertility and can have serious effects on their offspring. Although it is a long leap from flies to humans, could who you mate with influence your interactions with other females?
Many reproductive molecules and important bodily functions are conserved across the animal kingdom from flies to humans, so it is possible that what we found in flies here might be hinting to a common phenomenon across the tree of life. We need more studies to understand if this is the case!
Improved neuronal glucose uptake plus healthier eating might have anti-aging effects.
Researchers from Tokyo Metropolitan University have discovered that fruit flies with genetic modifications to enhance glucose uptake have significantly longer lifespans. Looking at the brain cells of aging flies, they found that better glucose uptake compensates for age-related deterioration in motor functions, and led to longer life. The effect was more pronounced when coupled with dietary restrictions. This suggests healthier eating plus improved glucose uptake in the brain might lead to enhanced lifespans.
The brain is a particularly power-hungry part of our bodies, consuming 20% of the oxygen we take in and 25% of the glucose. That’s why it’s so important that it can stay powered, using the glucose to produce adenosine triphosphate (ATP), the “energy courier” of the body. This chemical process, known as glycolysis, happens in both the intracellular fluid and a part of cells known as the mitochondria. But as we get older, our brain cells become less adept at making ATP, something that broadly correlates with less glucose availability. That might suggest that more food for more glucose might actually be a good thing. On the other hand, it is known that a healthier diet actually leads to longer life. Unravelling the mystery surrounding these two contradictory pieces of knowledge might lead to a better understanding of healthier, longer lifespans.
A team led by Associate Professor Kanae Ando studied this problem using Drosophila fruit flies. Firstly, they confirmed that brain cells in older flies tended to have lower levels of ATP, and lower uptake of glucose. They specifically tied this down to lower amounts of the enzymes needed for glycolysis. To counteract this effect, they genetically modified flies to produce more of a glucose-transporting protein called hGut3. Amazingly, this increase in glucose uptake was all that was required to significantly improve the amount of ATP in cells. More specifically, they found that more hGut3 led to less decrease in the production of the enzymes, counteracting the decline with age. Though this did not lead to an improvement in age-related damage to mitochondria, they also suffered less deterioration in locomotor functions.
But that’s not all. In a further twist, the team put the flies with enhanced glucose uptake under dietary restrictions, to see how the effects interact. Now, the flies had even longer lifespans. Curiously, the increased glucose uptake did not actually improve the levels of glucose in brain cells. The results point to the importance of not just how much glucose there is, but how efficiently it is used once taken into cells to make the energy the brain needs.
Though the anti-aging benefits of a restricted diet have been shown in many species, the team were able to combine this with improved glucose uptake to leverage the benefits of both for even longer lifespans in a model organism. Further study may provide vital clues to how we might keep our brains healthier for longer.
This work was supported by a research award from the Japan Foundation for Aging and Health, a JSPS KAKENHI Grant-in-Aid for Scientific Research on Challenging Research (Exploratory) (19K21593), NIG-JOINT (71A2018, 25A2019), a Grant-in-Aid for JSPS Research Fellows (18J21936) and Research Funding for Longevity Science (19-7) from the National Center for Geriatrics and Gerontology, Japan.
Reduced food intake, known as dietary restriction, leads to a longer lifespan in many animals and can improve health in humans. However, the molecular mechanisms underlying the positive effects of dietary restriction are still unclear. Researchers from the Max Planck Institute for Biology of Ageing have now found one possible explanation in fruit flies: they identified a protein named Sestrin that mediates the beneficial effects of dietary restriction. By increasing the amount of Sestrin in flies, researchers were able to extend their lifespan and at the same time these flies were protected against the lifespan-shortening effects of a protein-rich diet. The researchers could further show that Sestrin plays a key role in stem cells in the fly gut thereby improving the health of the fly.
The health benefits of dietary restriction have long been known. Recently, it has become clear that restriction of certain food components, especially proteins and their individual building blocks, the amino acids, is more important for the organism’s response to dietary restriction than general calorie reduction. On the molecular level, one particular well-known signalling pathway, named TOR pathway, is important for longevity.
“We wanted to know which factor is responsible for measuring nutrients in the cell, especially amino acids, and how this factor affects the TOR pathway”, explains Jiongming Lu, researcher in the department of Linda Partridge at the Max Planck Institute for Biology of Ageing. “We focused on a protein called Sestrin, which was suggested to sense amino acids. However, no one has ever demonstrated amino acid sensing function of Sestrin in a living being.” Therefore, Lu and his colleagues focused on the role of Sestrin in the model organism Drosophila melanogaster, commonly known as fruit fly.
Sestrin as a potential anti-ageing factor
“Our results in flies revealed Sestrin as a novel potential anti-ageing factor”, says Linda Partridge, head of the research team. “We could show that the Sestrin protein binds certain amino acids. When we inhibited this binding, the TOR signalling pathway in the flies was less active and the flies lived longer”, adds Lu. “Flies with a mutated Sestrin protein unable to bind amino acids showed improved health in the presence of a protein-rich diet.”
Particularly interesting: If the researchers increased the amount of Sestrin protein in stem cells located in the fly gut, these flies lived about ten percent longer than control flies. In addition, the increased Sestrin amounts only in the gut stem cells also protected against the negative effect of a protein-rich diet. Lu continues: “We are curious whether the function of Sestrin in humans is similar as in flies. Experiments with mice already showed that Sestrin is required for the beneficial effects of exercise on the health of the animal. A drug that increases the activity of the Sestrin protein might therefore be in future a novel approach to slow down the ageing process.”
Reference: Jiongming Lu, Ulrike Temp, Andrea Müller-Hartmann, Jacqueline Eßer, Sebastian Grönke and Linda Partridge, “Sestrin is a key regulator of stem cell function and lifespan in response to dietary amino acids”, Nature Aging, 2020. https://www.nature.com/articles/s43587-020-00001-7
Fruit flies may be able to teach researchers a thing or two about artificial intelligence.
University of Michigan biologists and their colleagues have uncovered a neural network that enables Drosophila melanogaster fruit flies to convert external stimuli of varying intensities into a “yes or no” decision about when to act.
The research, scheduled to publish Oct. 15 in the journal Current Biology, offers hints into how these decisions work in other species, and could perhaps even be applied to help AI machines learn to categorize information.
Imagine you are working near an open window. If the outside noise is low enough, you may not even notice it. As the noise level gradually increases, you start to notice it more–and eventually, your brain makes a decision about whether to get up and close the window.
But how does the nervous system translate that gradual, linear increase in intensity to a binary, “yes/no” behavioral decision?
“That’s a really big question,” said neuroscientist Bing Ye, a faculty member at the University of Michigan Life Sciences Institute and senior author of the study. “Between the sensory input and the behavior output is a bit of ‘black box.’ With this study, we wanted to open that box.”
Brain imaging in humans or other mammals can identify certain regions of the brain that respond to particular stimuli. But to determine how and when the neurons transform linear information into a nonlinear decision, the researchers needed a much deeper, more quantitative analysis of the nervous system, Ye said.
They chose to work with the model organism Drosophila, due to the availability of genetic tools that make it possible to identify individual neurons responding to stimuli.
Using an imaging technique that detects neuronal activity through calcium signaling between neurons, the scientists were able to produce 3-D neuroactivity imaging of the flies’ entire central nervous system.
“What we saw was that, when we stimulate the sensory neurons that detect harmful stimuli, quite a few brain regions light up within seconds,” said Yujia Hu, a research investigator at the LSI and one of the lead authors on the study. “But these brain regions perform different functions. Some are immediately processing sensory information, some spark the behavioral output–but some are more for this transformation process that occurs in between.”
When sensory neurons detect the harmful external stimuli, they send information to second-order neurons in the central nervous system. The researchers found that one region of the nervous system in particular, called the posterior medial core, responds to sensory information by either muting less intense signals or amplifying more intense signals, effectively sorting a gradient of sensory inputs into “respond” or “don’t respond” categories.
The signals get amplified through increased recruitment of second-order neurons to the neural network–what the researchers refer to as escalated amplification. A mild stimulus could activate two second-order neurons, for example, while a more intense stimulus may activate 10 second-order neurons in the network. The larger network can then prompt a behavioral response.
But to make a “yes/no” decision, the nervous system needs a way not just to amplify information (for a “yes” response), but to also suppress unnecessary or less harmful information (for a “no” response).
“Our sensory system detects and tells us a lot more than we realize,” said Ye, who is also a professor of cell and developmental biology in the U-M Medical School. “We need a way to quiet that information, or we would just constantly have exponential amplification.”
Using the 3-D imaging, the researchers found that the sensory neurons actually do detect the less harmful stimuli, but that information is filtered out by the posterior medial core, through the release of a chemical that represses neuron-to-neuron communication.
Together, the findings decode the biological mechanism that the fruit fly nervous system uses to convert a gradient of sensory information into a binary behavioral response. And Ye believes this mechanism could have far wider applications.
“There is a dominant idea in our field that these decisions are made by the accumulation of evidence, which takes time,” Ye said. “In the biological mechanism we found, the network is wired in a way that it does not need an evidence accumulation phase. We don’t know yet, but we wonder if this could serve as a model to help AI learn to sort information more quickly.”