It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Saturday, October 12, 2024
Galápagos finches could be singing a different song after repeated drought—one that leads to speciation
Summary author: Becky Ham
American Association for the Advancement of Science (AAAS)
Galápagos finches use their beaks to crush seeds and sing songs, so what happens to their musical trills when their beaks change to respond to new menus available under drought? Jeffrey Podos and Katie Schroeder found that the song might not remain the same after six cumulative future drought events that would likely reshape the finch beak. The projected changes in male mating songs could be so significant that they provide a pathway for ecological speciation, the researchers suggest. The researchers tested this idea by digitally modifying male mating songs of Darwin’s medium ground finches (Geospiza fortis) to sound like they might if beaks grew bigger under one, three or six cumulative future drought events. They then tested these “ghost of finches future” songs by playing them back to today’s male finches, as if the singers of the ghost songs were intruding on the males’ territory. Current males did not show signs of recognizing songs produced after six cumulative future drought events, treating the unseen producers of these songs as if they were no longer mating rivals. The study provides a better idea of how much “ecological change, and matched evolution of beaks and songs, would be required to elevate barriers to reproductive isolation,” the researchers write.
AMHERST, Mass. – They say that hindsight is 20/20, and though the theory of ecological speciation — which holds that new species emerge in response to ecological changes — seems to hold in retrospect, it has been difficult to demonstrate experimentally, until now. In research recently published inScience, biologists from the University of Massachusetts Amherst have identified a key connection between ecology and speciation in Darwin’s finches, famous residents of the Galápagos Islands, Ecuador. Prior work on these birds had established that birds’ beaks adapt to changing ecological environments, and that beak changes affect how the birds sing. But, until this paper, no one has yet been able to experimentally show that such changes drive the emergence of new species. The innovative key to this discovery? The ghosts of future finches.
Research recently published in Science by biologists from UMass has identified a connection between ecology and speciation in Darwin’s finches, famous residents of the Galápagos Islands, Ecuador. Prior work on these birds had established that birds’ beaks adapt to changing ecological environments, and that beak changes impact how the birds sing. The new study shows that beak-driven changes to song themselves can impact species recognition, and thus drive the separation of species.
“I started working with these birds 25 years ago,” says Jeffrey Podos, professor of biology at UMass Amherst and the paper’s senior author. “In my very first publication on the finches, back in 2001, I showed that changes in the beaks of Darwin’s finches leads to changes in the songs they sing, and I speculated that, because Darwin’s finches use songs to attract mates, then song changes related to beak evolution could perhaps catalyze ecological speciation.”
But, at the time, Podos had no smoking-gun experimental evidence with which to prove his hypothesis that environmentally driven changes to beak shapes were driving the emergence of new finch species. Part of the difficulty is that speciation is an historical process, which makes it tricky to document. Being able to watch it unfold as it happens would be like catching lightning in a bottle. As a workaround, Podos devised an experimental study that built on simulations, and he had some helpful leads to work with.
He knew, for instance, that beaks can either evolve powerfully to crush hard seeds or they can remain more delicate thereby enabling the faster movements necessary for more elaborate singing. “It takes serious motor performance to sing an intricate song, like that of the swamp sparrow,” says Podos, “and a big, powerful beak is just too clunky to manage the movements required.”
Thanks to decades’ worth of quantitative research that the wider biology community has conducted on the exact changes that the beaks of Darwin’s finches undergo due to different environmental changes, Podos realized that he could model how beaks would change into the future. In this case, he chose drought as the ecological driver, which tends to select for thicker-beaked finches. And he also knew that he could both predict, and then simulate, the songs of the finches as they would change through successive future episodes of drought.
“Essentially, we engineered the calls of future finches,” says Podos.
In general, the thicker the beak, the slower the songs and the narrower the bandwidth of the frequencies. Each subsequent drought event is predicted to render beaks that are increasingly thicker, which further should further slow the rate and decrease the bandwidths of the songs.
Finally, Podos and his team returned to the specific population of Darwin’s medium ground finches and played them the calls of the future finches.
“We found that there were no changes in the finches’ responses to our modified calls even when the simulated songs had changed by the equivalent of three drought events,” says Katie M. Schroeder, the paper’s co-author who participated in this research during her doctoral training under Podos at UMass Amherst. “But by six drought events, the had changed so much that the finches barely responded at all.”
These findings suggest that, because of the links between beaks and song, an entirely new species of Darwin’s medium ground finches could evolve in response to six major Galápagos droughts.
“Our research is not a conceptual revolution,” says Podos, “but it is an empirical, experimental confirmation of ecological speciation and its plausibility.”
This research was supported by the Charles Darwin Research Station and Galápagos National Park Service and the U.S. National Science Foundation.
The mating song of a male Darwin's medium ground finch. (AUDIO)
Caption
The mating song of a male Darwin's medium ground finch.
Credit
Jeff Podos
How drought drives speciation
Each drought event should increase the beak depth, which should in turn drive changes to the Darwin's medium ground finch song (l). The right panel gives a graphical representation of simulated beak changes and a spectrogram showing the corresponding projected changes in vocal performance.
Pipetting liquids into tiny test tubes, analyzing huge datasets, poring over research publications—all these tasks are part of being a scientist. But breaking this routine is essential. Time away from the usual work environment can spark creative ideas. Lab retreats, for instance, offer a great setting where researchers can engage with other peers, often leading to new collaborations.
The latter was true for Bernat Corominas-Murtra and Edouard Hannezo from the Institute of Science and Technology Austria (ISTA). Fascinated by a dataset showcased during a poster session at a collaborative retreat research group in Spain, Corominas-Murtra started a lively discussion with fellow researcher Dimitri Fabrèges, a postdoc from the research group of Professor Takashi Hiiragi at the Hubrecht Institute in Utrecht, The Netherlands. What started as a conversation has now turned into a publication in Science.
The international team of researchers has built a comprehensive atlas of early mammalian morphogenesis—the process of an organism developing shape and structure—analyzing how mouse, rabbit, and monkey embryos develop in space and time. Based on this atlas, they see that individual events such as cell divisions and movements are highly chaotic, yet the embryos as a whole end up looking very similar to one another. With this dataset, they propose a physical model that explains how a mammalian embryo builds structure from chaos.
From one to many
In animals, embryonic development starts when an egg cell is fertilized. This event triggers an array of consecutive cell divisions, known as cleavages. In a nutshell, a single cell divides into two, then two become four, four become eight, and so forth. Eventually, the bulk of cells form into a very organized structure called the blastocyst, from which all future organs and tissues develop. The entire process is termed morphogenesis.
“These early steps of embryonic development are key, as they set the stage for all subsequent developmental processes,” explains Edouard Hannezo. In some animals, for instance, in C. elegans—a transparent roundworm and one of the most studied model organisms by developmental biologists—the divisions in the early embryo are extremely well regulated and orientated the same way across different embryos, giving rise to organisms that all have the same number of cells. In mammalian species, however, it seems like divisions are much more random, both in timing and orientation. This raises the question of how reproducible mammalian embryonic development proceeds despite this disorder.
A detailed embryo map
To address this question, the Hiiragi group set out to image and quantitatively analyze many different embryos, to compare their similarities both within and between different mammalian species, from mice to rabbits and monkeys. Dimitri Fabrèges and colleagues created a so-called ‘morphomap’—a map to visualize high-dimensional morphological data. “It’s an imaging analysis pipeline showing how embryos behave in time and space—a precise atlas of an embryo’s morphogenesis,” explains Hannezo.
The map allowed the scientists to quantitatively analyze the developmental process by addressing questions such as the inter-embryo variability of development. With this dataset, the scientists were able to define what ‘normal’ morphogenesis looks like.
Fabrèges presented the morphomap at the lab retreat in Spain. The data showed that the first divisions after fertilization were not regulated across mice, rabbits, and monkeys. The cells divided randomly until they reached the 8-cell stage, a stage where all embryos suddenly started to look the same. “After looking very different in the first stages, embryos seemed to converge toward each other’s shape at the end of the 8-cell stage,” Hannezo continues. But how come? What brings structure to this chaos?
An embryonal Rubik’s cube—cell cluster optimizes its packing
Corominas-Murtra and Hannezo, both theoretical physicists, were fascinated by this dataset and set out to understand this process from a theoretical standpoint.
However, an embryo’s shape is highly complex, making it difficult to determine what it means for two embryos to be similar or different. The scientists discovered that they could effectively approximate the full complexity of the structure of an embryo simply by studying the configurations of the cell-to-cell contacts. “We think that we can derive most of the important details about the morphology of an embryo by understanding the arrangements of cells or knowing which cells are physically connected—similar to connections in a social network. This approach significantly simplifies data analysis and comparisons between different embryos,” says Corominas-Murtra.
Using this information, the scientists created a simple physical model for how embryos converge to a reproducible shape. The model shows that physical laws drive embryos to form a specific morphology shared among mammals.
By destabilizing most cell arrangements except a few selective ones that lower the surface energy of the embryo, physical interactions between cells can guide the formation toward a defined shape. In other words, cells tend to stick more and more together and this seemingly simple process actually drives the embryo through successive rearrangements to the most optimal packing. It’s like embryos solve their own Rubik’s cube.
No chaos, no structure
The results provide a detailed look at how the development of mammalian embryos is governed by variability and robustness. Without chaos, there is no structure; one needs the other. Both are essential parts of what constitutes ‘normal’ development. “We’re finally starting to have tools to analyze the variability of morphogenesis, which is crucial to understanding the mechanisms of developmental robustness,” Hannezo summarizes. Randomness seems to be a primary force in the generation of complexity in the living world.
By gaining more knowledge of what normal looks like, scientists also gain insights into abnormalities. This can be very helpful in areas, such as disease research, regenerative medicine, or fertility treatments. In the future, this knowledge can assist in selecting the healthiest embryo for in vitro fertilization (IVF), thereby improving the implantation success rate.
The schematic shows that the 4-cell stage embryo gives rise to many different shapes. At the beginning of the 8-cell stage, the embryos are driven toward the most optimal packing due to simple physical laws.
New Lancet Commission calls for urgent action on self-harm across the world
University of Bristol
Self-harm remains neglected worldwide, with at least 14 million episodes yearly. A new Lancet Commission, led by University of Bristol researchers, urges policy action on societal drivers and health services’ response to this pressing issue. The report, involving an international team of experts, is published today [9 October].
Self-harm is not a psychiatric diagnosis; it is a behaviour shaped by society, culture, and individual factors. The social determinants of health, particularly poverty, heavily influence the distribution of self-harm within communities.
Thisnew reporthighlights that at least 14 million episodes of self-harm occur each year[1], with the greatest burden felt in low- and middle-income countries (LMICs) and a higher incidence among young people. However, the authors suggest that this figure is likely an underestimate as people who self-harm often do not present to health services and there are few routine surveillance systems.
The authors also describe how attitudes lacking empathy, including in healthcare settings, can compound stigma around self-harm and keep people from seeking help. The report’s authors call on governments to recognise the public health impact of self-harm, and the need for mainstream and social media outlets need to report and publicise information about self-harm responsibly and sympathetically.
Paul Moran, Professor of Psychiatry and Head of the Centre for Academic Mental Health in the Bristol Medical School: Population Health Sciences (PHS) at the University of Bristol, and the Commission’s lead author said: “Self-harm signals deeper distress and affects millions globally, especially young people, yet it remains neglected due to stigma and lack of resources. This must change so that more people receive compassionate, tailored support.”
Hot dragonfly summer: species with darker wings have evolved to withstand heat and attract partners
Researchers found that male dragonflies with dark coloration on their wings have evolved to tolerate higher temperatures, possibly a decisive advantage in a warming world
Frontiers
image:
Infrared-spectrum image of an ornamented dragonfly from the genus Tramea. Lighter colors indicate hotter temperatures, ranging from 27 to 35 degrees Celsius across the image. Image: Noah Leith.
Temperature determines where species can live and if they are threatened by a warming climate. So, for a long time, biologists studied how heat tolerance affects survival. Yet, less is known about how thermal traits influence reproduction, which is directly linked to extinction risk.
Now, researchers in the US have examined if males of dragonfly species that produce sexual signals in the form of dark coloration on their wings are more resistant to heat. They published their results in Frontiers in Ethology.
“We show that dragonfly species that have evolved dark breeding coloration on their wings have also evolved the ability to tolerate high temperatures,” said Dr Noah Leith, a biologist at the University of Pittsburgh. “This finding paves the way for a whole new field of research exploring interactions between thermal traits and sexual signals.”
Dark spots, hot dragonflies
In dragonflies – same as in many animals – sexual signals can help them effectively locate mates, identify the correct species to mate with, and decide when to back out of mating contests.
Producing extensive dark wing coloration, though, comes at a cost. Dark ornaments absorb extra heat, increasing dragonflies’ body temperature. This can cause physiological stress or lead to males abandoning reproductive territories. “We see time and time again that animals will put their lives on the line to reproduce, even if it means encountering potentially lethal temperatures,” Leith said.
The researchers examined the wing coloration of 14 dragonfly species living in tropical climates and five species living in temperate climates. They found that species that possess dark, heat-absorbing wing coloration have evolved to be able to withstand higher heat stress before reaching critical thermal maxima. “This enhanced ability to tolerate high body temperatures is likely crucial for shaping how dragonflies may respond to the changing climates of the future,” Leith explained.
Beat the heat
Dark wing ornaments cause additional heating of 1°C to 2°C, which roughly equals the increased thermal maxima of ornamented species. Of the species studied, the arch-tipped glider (Tauriphila argo), a tropical species with very dark wing color patches near their core body, could tolerate the highest temperatures. Generally, this pattern of co-evolution was even stronger in tropical species.
Previous research showed that due to rising temperatures worldwide, some ornamented dragonfly species are evolving reduced wing coloration. The present results, however, suggest that even if those species lose their coloration, they will still have a leg up on adaptation to climate change because they’ve already evolved to tolerate hotter temperatures, the researchers said.
Preventing extinction
The study is one of the first to test whether thermal tolerance co-evolves with reproductive traits. “Our finding is particularly exciting because dark sexual coloration has evolved over and over across the tree of life and causes a wide variety of other animals to absorb extra heat too—from reptiles, to lions, and fruit flies,” Leith pointed out.
In a rapidly warming world, being able to predict which species are vulnerable to extinction is essential to preserving biodiversity, the researchers said. “Looking at vulnerability in only one aspect of animals’ lives is insufficient. We need a more nuanced understanding of how animals respond to changing environments as whole, complex organisms, in which their reproductive traits might influence their chances of surviving a heat wave, and vice versa,” Leith said.
While the researchers noted that looking at 19 species was plenty for their analysis, they said that there are thousands of dragonfly species. Future research should examine if similar patterns exist in other species, as well as in different types of animals. “It would be fantastic to someday test if heat tolerance co-evolves with sexual traits across life on Earth,” Leith concluded.
Ornamented dragonfly
Visible-spectrum image of a dragonfly with dark wing coloration form the genus Tramea. Image: Noah Leith.
Heat-absorbing sexual coloration co-adapts with increased heat tolerance in dragonflies
Article Publication Date
10-Oct-2024
The new fashion: clothes that help combat rising temperatures
University of South Australia
A team of international researchers has developed a natural fabric that urban residents could wear to counter rising temperatures in cities worldwide, caused by buildings, asphalt, and concrete.
As heatwaves become more prominent, cooling textiles that can be incorporated into clothes, hats, shoes and even building surfaces provide a glimpse into a future where greenhouse gas-emitting air conditioners may no longer be needed in our cities.
Engineers from Zhengzhou University and the University of South Australia say the wearable fabric is designed to reflect sunlight and allow heat to escape, while blocking the sun’s rays and lowering the temperature. They have described the textiles in the latest issue of Science Bulletin.
The fabric promises to bring relief to millions of city dwellers experiencing warmer and more uncomfortable temperatures caused by global climate change and fewer green spaces.
UniSA visiting researcher Yangzhe Hou says the fabric leverages the principle of radiative cooling, a natural process where materials emit heat into the atmosphere, and ultimately into space.
“Unlike conventional fabrics that retain heat, these textiles are made of three layers that are engineered to optimise cooling,” Hou says.
The upper layer, made of polymethyl pentene fibres, allows heat to radiate effectively. The middle layer, composed of silver nanowires, enhances the fabric’s reflectivity, preventing additional heat from reaching the body. The bottom layer, made of wool, directs heat away from the skin, ensuring that wearers remain cool, even in the hottest urban environments.
“In our experiment, when placed vertically, the fabric was found to be 2.3°C cooler than traditional textiles, and up to 6.2°C cooler than the surrounding environment when used as a horizontal surface covering.
“The fabric’s ability to passively reduce temperatures offers a sustainable alternative to conventional air conditioning, providing energy savings and reducing the strain on power grids during heatwaves.”
Zhengzhou University researchers Jingna Zhang and Professor Xianhu Liu say the technology not only addresses the immediate problem of urban heat islands, but also contributes to broader efforts to mitigate climate change and move towards more sustainable urban living.
It is hoped the technology could be adapted for even broader applications, including construction material, outdoor furniture and urban planning.
While the fabric holds significant promise, researchers say the current production process is costly, and the long-term durability of the textiles needs further investigation and government support before it can be commercialised.
“Whether consumers are willing to pay more for wearable fabrics depend on the cooling effect, durability, comfort and their environmental awareness,” the researchers say.
Every kid who has read a comic book or watched a Spider-Man movie has tried to imagine what it would be like to shoot a web from their wrist, fly over streets, and pin down villains. Researchers at Tufts University took those imaginary scenes seriously and created the first web-slinging technology in which a fluid material can shoot from a needle, immediately solidify as a string, and adhere to and lift objects.
These sticky fibers, created at the Tufts University Silklab, come from silk moth cocoons, which are boiled in solution and broken down into their building block proteins called fibroin. The silk fibroin solution can be extruded through narrow bore needles to form a stream that, with the right additives, solidifies into a fiber when exposed to air.
Of course, nature is the original inspiration for deploying fibers of silk into tethers, webs, and cocoons. Spiders, ants, wasps, bees, butterflies, moths, beetles, and even flies can produce silk at some point in their lifecycle. Nature also inspired the Silklab to pioneer the use of silk fibroin to make powerful glues that can work underwater, printable sensors that can be applied to virtually any surface, edible coatings that can extend the shelf life of produce, a light collecting material that could significantly enhance the efficiency of solar cells, and more sustainable microchip manufacturing methods
However, while they made significant progress with silk-based materials, the researchers had yet to replicate the mastery of spiders, which can control the stiffness, elasticity, and adhesive properties of the threads they spin.
A breakthrough came about purely by accident. “I was working on a project making extremely strong adhesives using silk fibroin, and while I was cleaning my glassware with acetone, I noticed a web-like material forming on the bottom of the glass,” said Marco Lo Presti, research assistant professor at Tufts.
The accidental discovery overcame several engineering challenges to replicating spider threads. Silk fibroin solutions can slowly form a semi-solid hydrogel over a period of hours when exposed to organic solvents like ethanol or acetone, but the presence of dopamine, which is used in making the adhesives, allowed the solidification process to occur almost immediately. When the organic solvent wash was mixed in quickly, the silk solution rapidly created fibers with high tensile strength and stickiness. Dopamine and its polymers employ the same chemistry used by barnacles to form fibers that stick tenaciously to surfaces.
The next step was to spin the fibers in air. The researchers added dopamine to the silk fibroin solution, which appears to accelerate the transition from liquid to solid by pulling water away from the silk. When shot through a coaxial needle, a thin stream of the silk solution is surrounded by a layer of acetone which triggers the solidification. The acetone evaporates in mid-air, leaving a fiber attached to any object it contacted. The researchers enhanced the silk fibroin-dopamine solution with chitosan, a derivative of insect exoskeletons that gave the fibers up to 200 times greater tensile strength, and borate buffer, which increased their adhesiveness about 18-fold.
The diameter of the fibers could be varied between that of a human hair to about half a millimeter, depending on the bore of the needle.
The device can shoot fibers that can pick up objects over 80 times their own weight under various conditions. The researchers demonstrated this by picking up a cocoon, a steel bolt, a laboratory tube floating on water, a scalpel partially buried in sand, and a wood block from a distance of about 12 centimeters.
Lo Presti noted that “if you look at nature, you will find that spiders cannot shoot their web. They usually spin the silk out of their gland, physically contact a surface, and draw out the lines to construct their webs. We are demonstrating a way to shoot a fiber from a device, then adhere to and pick up an object from a distance. Rather than presenting this work as a bio-inspired material, it’s really a superhero-inspired material.”
Natural spider silk is still about 1000 times stronger than the man-made fibers in this study. But with a little added imagination and engineering, the innovation will continue to improve and pave the way for a variety of technological applications.
“As scientists and engineers, we navigate the boundary between imagination and practice. That’s where all the magic happens,” said Fiorenzo Omenetto, Frank C. Doble Professor of Engineering at Tufts University and director of the Silklab. “We can be inspired by nature. We can be inspired by comics and science fiction. In this case, we wanted to reverse engineer our silk material to behave the way nature originally designed it, and comic book writers imagined it.”
