Thanks to a graduate student who is a “lifelong Swiftie”

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It’s meant to help lure prey

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It’s a remarkable act of impulse control

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The most carefully packed embryo of all the vertebrates

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There’s a lot of role reversal happening here

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Sex reversal may not be an evolutionary dead end after all

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Not every ant is a good samaritan

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Temperatures in the Arctic are increasing at a rate 4 times faster than the average global temperature. Scientists have documented the global effects of climate change, but there are still regions where these effects are less well known. This is the case for freshwater ecosystems in the Arctic.  

When the ground has been permanently frozen for 2 years, scientists call it permafrost. Permafrost contains soil, sand, rocks, and organic matter held together by ice. As temperatures rise, permafrost thaws, which can change groundwater flow paths. It can also alter a stream’s temperature, flow patterns, and nutrient loads by introducing new material from the permafrost.  

To determine how thawing permafrost affects Arctic ecosystems, scientists from the U.S. Geological Survey recently studied 10 headwater streams within the Brooks Range in the Noatak National Preserve of Alaska. The scientists studied streams with different amounts of permafrost and ice to test whether connections exist between permafrost, food webs, and populations of fish called the Dolly Varden and Arctic Graylings. They focused on these 2 species of fish because their migrations often indicate ecological shifts in the area.    

The scientists collected fish from the streams by temporarily stunning them, using a method called electrofishing, or by catching them in minnow traps. They manually identified each species they collected, then froze the fish and shipped them to a lab. Once in the lab, the scientists measured the length of each fish and used documented growth patterns to estimate its biomass. To calculate fish abundances, they divided their total biomass by the time spent electrofishing or trapping. Finally, they measured the energy density of each fish by burning it in a device called a bomb calorimeter. 

At each stream, the scientists took manual temperature measurements and deployed loggers that recorded the temperature every 15 minutes. They also deployed equipment at the bottom of each stream to record water pressure in 15-minute intervals and converted the data to depth, since pressure increases with depth. Then, they used wading rods to measure how much water was flowing through each stream at a given spot. 

They combined the depth and wading rod data to determine the flow rate of water in the streams over time. They used these data to identify unstable streams where water rose and fell rapidly. They also collected water samples from each stream and measured their nutrient concentrations, including dissolved organic carbon, nitrogen, and phosphorus, to determine water quality.   

Finally, they measured 2 types of smaller organisms that allow energy to flow through the food web to the fish, called microbial biofilms and macroinvertebrates. They used a hand-held device to estimate the types and amounts of biofilms, and nets to collect macroinvertebrates.

Once they had compiled these data, the team conducted a statistical analysis to compare the studied parameters and fish populations to the extent of permafrost in each area. They found that streams with more permafrost in the area had warmer temperatures, because the permafrost prevented water from infiltrating the soil to cool off. The streams with warmer temperatures, in turn, had lower abundances and biomass of Dolly Varden fish and Arctic Grayling with lower energy densities. They suggested that these results meant that the high temperatures had pushed the fish above their optimum temperature range. 

They also learned that the limited infiltration in permafrost areas caused rainfall to flow straight into the stream. This process created instability as the stream levels rose and fell rapidly. Fish in these unstable streams had lower energy densities, likely due to the harsher environment. 

Areas with greater permafrost also had higher concentrations of dissolved organic carbon and phosphorus, which stimulated the formation of biofilms at the bottom of the food chain. They noted that areas with more biofilms also had more macroinvertebrates and more Dolly Varden biomass. Since the Dolly Varden eats macroinvertebrates, this finding suggested that the lowest levels of the food web shape the health of species higher up. This is called the bottom-up effect, and means that areas with more biofilms and macroinvertebrates will likely have healthier and larger fish populations.  

The scientists explained that knowing how these factors influence Arctic fish populations can help researchers understand how thawing permafrost might affect Arctic ecosystems in the future. They anticipated that their data could help future researchers predict how these and other ecosystems will be impacted by changing landscape dynamics caused by global warming. 

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Horseshoe crabs are marine animals more closely related to spiders than crabs. These animals have existed for more than 450 million years, and are sometimes called “living fossils” because they appear to have changed very little throughout their evolutionary history. However, horseshoe crabs have a poor fossil record, so this apparent lack of change could also be due to a lack of evidence, particularly when it comes to their reproduction. Scientists want to know: Are horseshoe crabs truly living fossils?

Modern horseshoe crabs reproduce by releasing hundreds of eggs and sperm into tidal waters, via a process called external fertilization. Until now, scientists have assumed that horseshoe crabs have always reproduced this way. But paleontologists have only found 3 fossil horseshoe crabs from the past 252 million years with their reproductive systems preserved, so this assumption is mainly based on an absence of evidence to the contrary. 

Scientists in the past interpreted the horseshoe crab’s long history of external fertilization as indicative of its evolutionary consistency. However, James Lamsdell and colleagues recently discovered a new fossil species of horseshoe crab in the 450 million-year-old Big Hill Formation in Michigan that challenges this assumption. 

To study the specimen, the scientists photographed it under 2 types of microscopes. The first type of microscope used polarized light to see structures in the fossil that may have blended into the rock, like putting on special glasses to see subtle textures. The second type of microscope used fluorescent light to reveal soft tissue in the fossil. Only some tissues, like ovarian tissue and preserved eggs, glow under fluorescence, so this method helped the team rule out non-biological structures, like bubbles, cracks, or minerals. 

The researchers found that their analytical techniques revealed remarkable details about the ancient horseshoe crab. One unique feature of the fossil was the shape of its exoskeleton. The fossil’s exoskeleton had a more shovel-like appearance than that of modern horseshoe crabs, which are less elongated and more round. It was also about 11 times smaller than a modern adult horseshoe crab. 

The researchers also discovered that the fossil preserved an intricate network of ovaries containing unfertilized eggs. This ovarian network lined the interior surface of the shell in a band of interconnected tubes, preserving both unfertilized eggs and developing eggs. They noted that the fossil eggs were all about 0.1 to 0.15 millimeters in diameter, about the same width as a human hair. This size consistency suggested that all the eggs developed at the same time, via a process called synchronous development. 

Since the fossil crab’s ovarian tubes contained developing eggs, it was an adult, meaning that the earliest adult horseshoe crabs were significantly smaller and shaped differently than modern adult horseshoe crabs. Despite their differences in size and shape, the fossil horseshoe crab’s reproductive system closely mirrored its modern one, in terms of its ovarian system and synchronous development of eggs. As in previous studies, it showed no evidence of internal fertilization.

The researchers concluded that the earliest horseshoe crabs also reproduced through external fertilization. This fossil horseshoe crab is more than 215 million years older than preexisting fossils preserving evidence of external fertilization, and suggests that the horseshoe crab’s mode of reproduction has been conserved for almost half a billion years!

However, the team’s findings reveal a more nuanced evolutionary history for the horseshoe crab than previously assumed. Although they’ve maintained the same reproductive system for almost half a billion years, the size and shape of their exoskeleton have changed. This discovery reveals that different parts of the horseshoe crab evolved at different rates. It seems that horseshoe crabs are not entirely the living fossils scientists once thought… while their bodies have evolved, their reproduction has endured.

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Cranial scans reveal a brain with clever sensory adaptations

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The first experiment that Christoph Adami discusses is one where scientists transported lizards from one island to another.

Source

The features of fish that have passed through the Suez Canal provide clues

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The spots on a leopard, the stripes on a zebra, and the mask on a raccoon are all types of coloration in mammal fur, referred to as pelage. Scientists have struggled for a long time to understand how these colorations evolved. A team of researchers recently discovered how to reconstruct the colors of ancient mammal fur using cell structures that contain the chemical pigment melanin, known as melanosomes. They hope to use this understanding of ancient mammal pelage to determine how they lived and what their environments were like.

To decipher the color of ancient mammal fur, the researchers constructed a statistical computer model to predict their fur colors based on the shape of their melanosomes. First, they needed to understand how the shapes of melanosomes control fur color in modern mammals. To measure the length and width of the modern melanosomes, the scientists used a beam of electrons like a flashlight to map them in great detail, a technique called scanning electron microscopy.

They measured the length and width of 2,615 melanosomes from the fur of 116 different living mammal species, including a Red Panda, a German Shepard, and one or more species of most types in the mammalian classification. Then they recorded the wavelengths of light reflected off each melanosome using a microspectrophotometer. These wavelengths represented the exact color of hair from each melanosome they measured. This means they now had a quantitative measurement of the color of each hair to compare with its corresponding melanosome length and width.

When they examined their data, the researchers found that spherical melanosomes produced brighter fur colors, like reds and oranges, while elongated melanosomes produced darker fur colors, like browns and grays. The researchers plotted the microspectrophotometric measurements for each melanosome as a graph showing how much light it absorbed across each possible wavelength, creating reflectance curves. Based on these data, the researchers used computer software to create a statistical model that could predict reflectance curves, and therefore color, from melanosome shape alone.

Once the researchers created a model, they needed to find fossilized mammal melanosomes to predict their fur color. Mammal fossils are rare, and pieces of cells are only preserved in the most immaculate fossil deposits. In fact, these researchers only found 6 fossils of this caliber, from Mesozoic rocks deposited around 250 million years ago, soon after mammals evolved. 

The fossils came from 2 world-renowned deposits in Northeastern China, the Yanliao and Jehol biotas. They selected 5 previously studied fossils from these locations, including 1 specimen of Megaconus mammaliaformis, 1 specimen of Vilevolodon diplomylos, 2 specimens from the group Docodonta, and 1 specimen from the group Eutheria. All of these animals were small, rodent-like mammals. The researchers also discovered a new species of tree-dwelling mammal, Arboroharamiya fuscus.

The scientists used scanning electron microscopy to measure a total of 2,159 fossilized melanosomes to refine their color predictions. The fossilized melanosomes were all slightly elongated spheres and had far fewer differences in shape than in modern mammals. The researchers used their model to predict reflectance curves based on the shapes of the fossil melanosomes to determine the ancient mammals’ colors. They found that all the extinct mammals they examined likely had dark brown fur without any color patterns.

Based on these findings, the researchers suggested that most, if not all, early mammals were nocturnal, like many dark-colored mammals today. They suggested that this nocturnal lifestyle probably helped them survive the meteorite impact that wiped out the dinosaurs 100 million years later. While dinosaurs were unable to survive in the post-impact wasteland, these smaller, dark-colored mammals were more resilient and thrived in the aftermath. As mammals filled the ecological roles left by the dinosaurs, they evolved new color patterns, some based solely on camouflage, and others on new factors, like sexual selection and visual communication.

The researchers concluded that their model can predict fossilized mammal colors and help determine how these ancient animals lived. Notably, their data suggest that mammals likely stayed small and nocturnal throughout the Mesozoic until the dinosaurs were gone. Future researchers could use similar methods to uncover exactly how mammals evolved the colors we see today. For example, studying mammals closer to the impact event could reveal if it took a long time to develop diverse fur patterns, or if they began before the dinosaurs’ demise. Ultimately, similar studies could help determine whether the extinction of dinosaurs was necessary for the rise of mammals.

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The ocean giants deploy tiny solutions to counteract their own buoyancy

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The volatile compound they emit induces temporary infertility in other females

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3-D avatars of macaques fool their flesh-and-blood counterparts—up to point

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It’s one of only a handful of new monkey species identified on the continent in the last 75 years

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In March 2021, the carcasses of at least 260 marine organisms from 81 species, including large animals called megafauna, washed ashore in South Africa. Scientists questioned whether this event was the result of an extreme temperature drop that can happen when deep, cold water rises to the surface along coastlines. Scientists refer to these rapid cooling events as coastal upwelling. 

Climate change is making oceans warmer, but it’s also making coastal upwelling stronger, with unknown consequences for marine megafauna. Scientists recently studied 2 boundary currents that are rapidly warming and creating strong upwelling near the edges of sharks’ geographic ranges: the Agulhas Current in southern Africa and the East Australian Current in eastern Australia. They wanted to determine whether climate-driven changes in upwelling zones are making cold-shock events more frequent and intense, and how these events are pushing sharks beyond their temperature limits. 

First, the researchers analyzed sea surface temperature data from satellites to see if rapid cooling from upwelling caused the mass marine die-off in 2021. They also obtained hourly temperature recordings from temperature loggers to measure subsurface temperature changes during the event. They found that during the March 2021 event, sea surface temperatures along the coast dropped by up to 7°C (12°F) in less than 48 hours, from 24°C (75°F) to below 17°C (63°F). Subsurface temperatures dropped faster, by more than 9°C (16°F) in 24 hours, from 21°C (70°F) to 12°C (54°F). 

Bullsharks experience physiological stress at temperatures below 19°C (66°F), which is near their lower thermal limit, when migrating through rapid cooling zones. Therefore, the researchers deduced that during the 2021 cold-shock event, the sharks were exposed to temperatures several degrees below their thermal limit, possibly more than 5°C (or 10°F) colder. 

The researchers also tagged 66 bull sharks with acoustic and satellite transmitters – including 41 at the Agulhas Current in South Africa and 25 at the East Australian Current in eastern Australia – to determine how they responded near their lower thermal limits in these zones. The acoustic tags record when sharks pass underwater receivers, providing information on their movements, locations, and water depths at those specific locations. In contrast, satellite tags continuously record the water temperatures and depths the sharks experience over time. 

The researchers used these data to compare sharks living in warm subtropical waters with those living in cooler waters at the edge of their temperature range. The researchers found that low temperatures that persisted for long periods prevented the sharks and other megafauna from physiologically recovering. They saw that some sharks try to swim to shallower depths and look for warmer water, but cooling sometimes happened faster than they could respond. 

The researchers also obtained wind records from the South African Weather Service to determine if upwelling-favorable winds happened before the 2021 event. They reported strong easterly winds pushing cold water on the surface along the coastline immediately before the event occurred. Because the cooling, strong winds, and animal deaths happened at the same time and place, the researchers inferred that upwelling was the main reason for the die-off.

Finally, the researchers examined 41 years of sea surface temperature data and used mathematical models to compute changes in the frequency and intensity of these events. Their analysis showed that rapid cooling events linked to upwelling can last a lot longer than the usual 1 to 3 days. For example, the March 2021 event lasted for 7 days. 

They found that these events have increased in both frequency and intensity in the past decades, and produce more extreme temperature drops than typically happen within 24 hours. Their results suggested that the 2021 die-off was part of an increasing trend, where warming oceans allow species to move into different areas, but intense upwelling can suddenly expose them to fatal cold events. This pattern is what scientists call a climate bait-and-switch. 

The researchers concluded that climate change is making coastal upwelling stronger, which can push marine megafauna beyond their thermal limits, even when initial warming appears to be beneficial. Their findings highlight an understudied aspect of climate change in the context of how temperature and upwelling cause shifts in species survival. They concluded their findings could help predict how marine ecosystems respond to future changing ocean conditions.

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The elusive creatures were thought to have vanished

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A new look at puma-human encounters in the mountains of California

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