Timeline of Photosynthesis on Earth


Timeline of Photosynthesis on Earth

 

Photosynthesis evolved early in Earth’s history. The rapidity of its emergence suggests it was no fluke and could arise on other worlds, too. As organisms released gases that changed the very lighting conditions on which they depended, they had to evolve new colors.

4.6 billion years ago — Formation of Earth

3.4 billion years ago — First photosynthetic bacteria
They absorbed near-infrared rather than visible light and produced sulfur or sulfate compounds rather than oxygen. Their pigments (possibly  bacteriochloro­phylls) were predecessors to chlorophyll.

2.4–2.3 billion years ago — First rock evidence of atmospheric oxygen

2.7 billion years ago — Cyanobacteria
These ubiquitous bacteria were the first oxygen producers. They absorb visible light using a mix of pigments: phyco­bilins, carotenoids and several forms of chlorophyll.

1.2 billion years ago — Red and brown algae
These organisms have more complex cellular structures than bacteria do. Like cyanobacteria, they contain phycobilin pigments as well as various forms of chlorophyll.

0.75 billion years ago — Green algae
Green algae do better than red and brown algae in the strong light of shallow water. They make do without phyco­bilins.

0.475 billion years ago — First land plants
Mosses and liverworts descended from green algae. Lacking vascular structure (stems and roots) to pull water from the soil, they are unable to grow tall.

0.423 billion years ago — Vascular plants
These are literally garden-variety plants, such as ferns, grasses, trees and cacti. They are able to grow tall canopies to capture more light.

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Complex Life Could Be Vastly Older Than Thought


New algae fossil discovery may reset the evolutionary time line

Complex Life Could Be Vastly Older Than Thought
This photo shows a light microscope image of cellular tissue from a “fleshy” specimen resembling red algae, named Ramathallus lobatus.
Credit: Therese Sallstedt, Swedish Museum of Natural History

It was around 1.6 billion years ago that a community of small, bright red, plantlike life-forms, flitting around in a shallow pool of prehistoric water, were etched into stone until the end of time. Or at least until a team of Swedish researchers chipped their fossilized remnants out of a sedimentary rock formation in central India.

Research published this week in PLoS Biology suggests this collection of ancient, newly analyzed fossils—unearthed a few years back—are in all likelihood red algae. If that proves true, it would imply that complex, multicellular life evolved a lot earlier than previously thought—and that the evolutionary family tree of life on Earth might need a major pruning.

Earth’s first traces of life probably showed up around 3.5 billion years ago, a billion years or so after our planet formed. Just when these simple, single-celled organisms—classified as “prokaryotes” due to their lack of a nucleus—evolved into multicellular, nucleated forms called “eukaryotes” is a matter of debate. Alga, a eukaryote, is thought to be one of the oldest forms of complex life. And given that previous fossil finds had dated red algae back just 1.2 billion years, the new discovery could reset the evolutionary time line by nearly half a billion years.

The apparent red alga was found embedded in fossilized sheets of cyanobacteria, widely believed to be the first oxygen-producing life-forms to have arisen and a precursor all to algae and plants. (Although not all algae are considered “plants” per current classification, they are all considered plantlike because they use photosynthesis to produce energy). By dissolving surrounding rock with acetic acid—a common method used in excavating fossils—the new paper’s authors unearthed what appear to be two forms of red alga: a tubular strain resembling a segmented pool noodle and a fleshier variety composed of multilayered collections of cells.

The authors used a technique called synchrotron-based x-ray tomographic microscopy to construct a three-dimensional model of the fossils, and to identify internal cellular structures that the organisms probably used for energy production. Radioactive dating was used to confirm the fossils’ age. “The new fossils provide tangible evidence that advanced multicellularity, at least in plants, appeared much earlier than previously thought,” says Stefan Bengtson, senior author of the new paper and professor emeritus of paleozoology at the Swedish Museum of Natural History. “They suggest that the timing of early eukaryotes may have to be drastically revised.”

Without the presence of DNA—which does not hang around in samples so staggeringly old—it is impossible to confirm the new fossils are bygone red algae. Bengtson admits as much. But he also believes the fossils’ structures bear a strong resemblance to that of red alga.

Paul Strother, a Boston College biologist who studies the evolution of algae and plants, and who was not involved in the new research, is not sold. “If these are real…they still do not show any sort of cell differentiation. All the cells are basically the same, and these forms do not represent complex multicellularity,” he says.

University of Wisconsin–Eau Claire biology chair, Wilson Taylor, who was also uninvolved in the work, points out that even if the new samples are really algae, the search for the origins of complex life still has a long way to go. “If a red alga really had evolved by this time…this implies a prior period of eukaryotic evolution of some length,” he says. “How long before the 1.6-billion-year horizon eukaryotes arose, based on that early occurrence, is anyone’s guess.” Taylor explains that eukaryotes—which comprise virtually all nonmicroscopic life on Earth—likely arose when one prokaryote engulfed another and found some symbiotic benefit that kept the relationship going. But how long it took this vital communion to take hold in the evolutionary process is unknown.

As Bengtson points out, whereas red algae are not a direct precursor to plants—that honor belongs to green algal ancestors—they do closely descend from one common ancestor of all plants on Earth today. Assuming the new findings are true, a major question now facing paleobotanists is why it took another billion years for larger, more complex organisms to flourish.

It was not until between 600 million and 500 million years ago that higher plants and animals began evolving. Submarine algae, bobbing amid blankets of microbes, gradually gave way to what we know as plants. Plants made their way to shore, shaping a new landscape that would come to include complex fungi and, eventually, terrestrial animals.

Bengtson hopes to further study early algal populations in order to better pinpoint where and when they arose, and why they lingered in the sea for so long. Although evolution’s tributaries will no doubt continue to be modified—some rerouted, others reset—scientists can assume they are closing in on an accurate lineage of life on Earth; and that our photosynthetic, oxygen-producing co-dwellers, on which our lives rely, have speckled the planet we call home for much of its existence.

Big Data Renews Fight Over the Origin of Animals


A new study is the latest in the long-running dispute over which lineage—sponges or comb jellies—is the ancestor to all animals

Big Data Renews Fight Over the Origin of Animals
The debate over which lineage came first — sponges (pictured) or comb jellies — is far from settled.

Evolutionary biologists have battled for years over which animal lineage came first — sponges or comb jellies. The answer could transform how scientists understand the evolution of the human nervous system, digestive system and other complex traits.

A study published on March 16 in Current Biology, sides with the sponges, using an unprecedented array of genetic data to deduce that they were the first to branch off from the animal tree of life1. Sponges are simple creatures that lack a head, nerves and guts, so the conclusion makes intuitive sense. But big data doesn’t necessarily lead to better answers, some researchers warn.

“They’ve got a large data set, but almost certainly this is not the final word,” says David Hillis, an evolutionary biologist at the University of Texas at Austin who was not involved with the project. “This is just such a tough problem to solve.”

Peering back through 600 million years of transformation is hard. It seems that every animal descends from ancestors on one of five branches near the base of the tree. But these five groups look very different from one another today. There are sponges, comb jellies, cnidarians (including sea anenomes, corals and jellyfish), bilaterally symmetrical animals (such as humans and clams) and obscure, microscopic worms called placozoans.

Battle of the branches

For the better part of the past century, zoologists arranged these branches according to their judgements of what was simple and what was complex. Sponges fell to the bottom branch, and bilaterally symmetrical animals resided higher up. But in 2008, a genetic analysis published in Nature put comb jellies, rather than sponges, near the root of the evolutionary tree2.

This arrangement rattled evolutionary biologists because it upended the idea that animal complexity increased over time. It implied that nerves and other characteristics evolved independently in different lineages, and were subsequently lost in sponges. Since then, studies have supported or contradicted the rearrangement, but all have been plagued by problems.

In the most recent study1, the authors attempt to resolve one of the biggest challenges in building evolutionary trees based on DNA comparisons. Some genomes evolve faster than others, and fast-evolving genomes from unrelated animals can converge on a similar sequence. “By chance, lineages accumulate genetic similarities not due to a shared history but due to random change,” explains Michaël Manuel, an evolutionary biologist at the Institute of Biology Paris-Seine, and the study’s senior author.

This problem is called long-branch attraction, because mathematical models depict genetic changes as additional lengths on the branches of the diagrams they produce. Long branches can cluster together on a tree as a result of these convergences, or because their genetic sequences are so unlike others in the tree. Either way, the clustering suggests that two lineages are related when they’re not. Manuel suspects that the long branches of non-animals such as fungi attract the comb-jelly lineage because, for unknown reasons, comb-jelly genomes have accumulated an unusual number of changes over time.

Flip-flopper

To skirt such long-branch attraction, Manuel and his colleagues analyzed 1,719 genes from an unparalleled range of species. It took computing power from Canada, Germany, Belgium and France to crunch the numbers. The team also tested several mathematical models that accounted for biological phenomena, including the fact that certain genetic changes are more likely than others. They chose a model called CAT, partly because of how well it reproduced sections of the animal tree that have already been confirmed.

The results from the CAT model placed sponges on the earliest branch of the animal family tree. Some other models that the team used had put comb jellies at the base. “The fact that the results flip-flop with different models is a bad sign,” says Hillis, who was not involved with the work.

Casey Dunn, an evolutionary biologist at Brown University in Providence, Rhode Island who also was not involved in the study, agrees. “Unfortunately, this is telling us that adding more species data isn’t moving the needle on the problem.”

In the future, Hillis suggests, biologists should explore genomic data that are less prone to long-branch attraction, because the chance of random convergence is lower. For instance, genes rarely insert themselves into other genes, but it happens. Hillis concedes that finding a solution will not be easy. “But this tree really matters,” he says. “It changes how we understand major things that happened in evolution.”

Say Hello to Dickinsonia, the Animal Kingdom’s Newest (and Oldest) Member


Half-billion-year-old fossils reveal new details about one of the most mysterious chapters in Earth’s history.

Say Hello to Dickinsonia, the Animal Kingdom's Newest (and Oldest) Member
A fossilized imprint of Dickinsonia, mysterious organisms that may have been Earth’s earliest animals.

Nearly 600 million years ago Earth’s continents were lifeless lands—but the oceans were teeming. Below the white-capped waves a dizzying variety of life-forms grazed blindly on gooey mats of microbes that covered the seafloor.

Thought to represent the earliest flowering of complex multicellular life on our planet, these creatures arose in a world devoid of predators, and had no need for hard protective carapaces or skeletons. Their soft, squishy bodies resembled, tubes, fronds or even thin, quilted pillows; they bore scant similarity to the anatomy of animals today. This ancient biosphere seems quite alien—and yet these organisms must be our early ancestors.

At least that is the story according to a new paper published today in Science, where researchers argue an iconic fossil from this time period is the oldest known animal that would have been visible without the help of a microscope. If correct, the finding settles a 70-year-old debate and could help explain the emergence of more advanced life-forms on our once-barren planet.

The fossils from some 575 to 541 million years ago, from a time known as the Ediacaran period, represent the earliest known complex life on Earth—meaning these creatures were neither microscopic single-celled organisms nor simple multicellular colonies of unicellular microbes. Yet because of their remoteness from us in planetary and evolutionary time—and the fact flesh fossilizes far less readily than shell or bone does—their true nature has mostly remained unknown. In 1947, for example, when scientists in Australia first discovered the segmented, pancake-shaped fossils of Ediacaran creatures dubbed Dickinsonia that can run up to one meter in length, they thought the strange organisms were an early form of jellyfish. And yet fossilized Dickinsonia and other Ediacarans exhibit no obvious characteristics such as appendages, a mouth or a gut that would link them to anything in the animal kingdom. As such, their place on the family tree of life has been quite contentious: If Dickinsonia were not jellyfish, perhaps they were instead annelid worms or mushrooms, or enormously oversize lichens or single-celled organisms.

The problem is that although Dickinsonia fossils have now been spotted at dozens of sites across the globe, they are typically found solely as two-dimensional imprints in sandstone. “It would be like trying to judge the structure of our modern world if all you had was footprints,” says Guy Narbonne, a paleontologist at Queen’s University in Ontario who was not involved in the study. Then in 2016, Ilya Bobrovskiy, a graduate student at Australian National University, made a startling discovery, stumbling upon Dickinsonia fossils in Russia that were essentially mummified in a mixture of clay and sandstone. “Just imagine finding a T. rex that is so well preserved you still have the hard-tissue, the skin, maybe even a mummified eye,” says Bobrovskiy’s PhD Advisor Jochen Brocks, a biogeochemist at the Australian National University. “Think about how much we would learn about dinosaurs! That’s in principle what my student found.”

The potential was enormous. “I’m in awe of this study because it’s a spectacular opportunity to get molecular information about a fossil that has been so enigmatic,” says Roger Summons, a geobiologist at Massachusetts Institute of Technology who was not part of the work. Indeed, when Brocks and his colleagues analyzed the samples, they uncovered cholesteroids: the molecular fossils of cholesterol, a distinctive signature of animal life. Whether animal, vegetable or otherwise, every Earthly organism is composed of cells bounded by layers of lipid molecules; only animals, however, have cholesterol in their cell membranes. So spotting cholesteroid meant Dickinsonia were in fact animals. Still, the detection could have been due to contamination—a careless brush of a finger against a fossil, for instance, could immediately transfer cholesterol-containing cells and produce an artificial signal of ancient animal life. So, Brocks and his colleagues carefully scrutinized the rocks surrounding the mummified Dickinsonia as well. There, rather than cholesteroids they found stigmasteroids, a molecular fossil commonly associated with green algae. That difference, they say, all but confirms the cholesteroid came from the fossils themselves and not from contamination, cementing Dickinsonia’s foundational status in the animal kingdom.

“I think the paper puts to bed any suggestion that they were otherwise,” Summons says. “To me, chemistry doesn’t lie.” Not only does it prove that Dickinsonia was an animal—it also now holds the record as the oldest macroscopic creature in the fossil record. And that is a crucial finding. At the end of the Ediacaran (which marks the beginning of the next period, the Cambrian), an evolutionary uprising overturned the simple and peaceful ecosystems that had reigned for 30 million years, setting the stage for our modern world. The Cambrian explosion, as it is called, produced animals with far more familiar anatomies and behaviors, such as creatures with shells, spines, thrashing limbs and tooth-rimmed jaws that could trap and devour prey. But scientists still do not know what sparked this eruption of life-forms.

Based on his team’s latest findings, Brocks argues the answer must lie somewhere within the evolutionary vagaries of Ediacaran biota. That is different from previous notions that suggested the Ediacarans were not animals at all, causing some scientists to argue the creatures were evolutionary dead ends wholly distinct from their Cambrian successors. For Dickinsonia, at least, scientists can now argue these strange soft-bodied beings were the progenitors of the Cambrian animals that swept over the planet, and thus were our ancestors.

Ultimately, this finding could help scientists better understand the complicated interplay of geology and biology that triggered the evolution of complex life on Earth—and perhaps on other worlds as well. Douglas Erwin, a paleobiologist at the Smithsonian National Museum of Natural History who did not take part in the study, is hopeful it will bolster the search for life elsewhere in the solar system because it demonstrates how faint chemical traces—rather than the more obvious analysis of fossil morphology—can uncover new, previously overlooked biological details. That is crucial because beyond Earth, he says, “we’re more likely to find fossils of something than we are to find something sticking its head up and waving.”

Exploring the Mysterious Life of One of Earth’s First Giant Organisms


Strange creatures known as “rangeomorphs” could help paleontologists understand the origins of animal life

Exploring the Mysterious Life of One of Earth's First Giant Organisms
An artist’s depiction of the extinct giant, frondshaped
organisms known as rangeomorphs. 

Paleontologists unearthed a strange sight in Newfoundland in the early 2000s: an ancient fossil bed of giant, frond-shaped marine organisms. Researchers had discovered these mysterious extinct creatures—called rangeomorphs—before, but they continue to defy categorization. Now scientists believe the Newfoundland fossils and their brethren could help answer key questions about life on Earth.

Rangeomorphs date back to the Ediacaran period, which lasted from about 635 million to 541 million years ago. They had stemlike bodies that sprouted fractal-like branches and were soft like jellyfish. Scientists think these creatures grew to sizes until then unseen among animals—up to two meters long. After they went extinct, the planet saw an explosion of diverse large animal life during the Cambrian. “Rangeomorphs are part of the broader context of what was going on at this time in Earth’s history,” says study co-author Jennifer Hoyal Cuthill, a paleobiology research fellow at the Tokyo Institute of Technology. Figuring out how rangeomorphs grew to such great sizes could help provide context for understanding how big, diverse animals originated and how conditions on Earth—which were shifting around this time—may have affected the evolution of life.

To better understand these connections, Hoyal Cuthill and University of Cambridge paleontologist Simon Conway Morris analyzed several rangeomorph fossils. The pair performed a micro CT scan on one well-preserved fossil of a species called Avalofractus abaculus, found in Newfoundland, to examine its 3-D structure in fine detail. They also took photographic measurements of two other specimens for comparison.

The researchers examined various aspects of the rangeomorphs’ stems and branches, then used mathematical models to investigate the relation between the fossils’ surface areas and volumes. Their models, combined with the fossil observations, revealed that the organisms’ size and shape appeared to be governed by the amount of available nutrients, according to the study, published recently in Nature Ecology & Evolution. This may explain why they could reach such large sizes during a period when Earth’s geochemistry was changing.

But other experts are hesitant to generalize in this way. “This is an interesting finding that supports the growing consensus among researchers that rangeomorphs had the potential to grow differently in response to their environment,” says Jack Matthews, a research fellow at the Oxford University Museum of Natural History, who was not involved in the work. But “it is perhaps premature for this study to apply its finding to all rangeomorphs.”

If the explanation turns out to be correct, though, Hoyal Cuthill says, it could provide an answer for “what links this amazing appearance of larger organisms in the fossil record with [what was] happening on Earth.”

Here’s Proof of Evolution You Can Find on Your Own Body


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It might sound a little offensive, but your body is a museum, full of ancient relics no one really needs anymore. From your wisdom teeth to that weird way some of us can wiggle our ears, so much of how we ended up as humans reflects what our animal ancestors needed for survival.

As this video by Vox explains, these strange remnants, that stuck around only because they’re not ‘costly’ enough to have disappeared across many millennia, only make sense within the framework of evolution by natural selection.

Here’s one you can see for yourself right now: if you hold your arm out, and touch your thumb to your pinky, you’ll probably see a raised tendon in the middle of your wrist.

Right? If you don’t have that, lucky you – you’re among the 10-15 percent of humans on Earth who were born without this prominent feature in one or both of their arms.

This tendon connects to the palmaris longus, a muscle that most of us have, but there seems to be no real reason for it being there. As the video explains, research has found that the presence of this muscle in our forearms does not give us any more discernible arm or grip strength than people born without the muscle.

In fact, it’s so inconsequential, surgeons often remove it and use it for reconstructive or plastic surgery procedures elsewhere on the body.

So why did we end up with such a useless piece of tissue? Scientists have found that, while palmaris longus is present in many species of mammals today, it’s most developed in those that use their forearms to move around – such as lemurs and monkeys.

Here’s another one: have you figured out how to manipulate the three muscles around the base of your ear so you can wriggle it ever-so-slightly?

Good job – you’re demonstrating how another evolutionary remnant has transitioned from an essential piece of equipment for our animal ancestors to a party trick no one cares about in humans.

Just like many nocturnal animals today – such as rabbits, gazelles, and cats – rely on the wide range of angles their ears can turn and face to better locate the origin of a sound, the creatures we’ve evolved from would have used the same trick millions of years ago.

And we haven’t completely lost all of the ‘equipment’ they would have used.

As Vox points out, not only did humans retain three of the muscles involved in ear movement, studies have shown that these muscles still respond to sound. They don’t respond strongly enough to make our ears move anymore, but they appear to give it their best shot.

From goosebumps and tailbones, to that adorable thing babies do when they grasp whatever you put in front of their tiny fingers, there are plenty of other examples of weird things our bodies have that hint at the abilities of our ancient ancestors.

Ancient Teeth With Neanderthal Features Reveal New Chapters of Human Evolution


Crime-drama fans know that forensic scientists can ID the remains of long-missing persons by examining their teeth. To solve even more ancient mysteries, anthropologists use the same kind of cutting-edge tooth technology, and a European team may have cracked a very cold case indeed—one that’s almost half a million years in the making.

A fossil tooth study published today in the journal PLOS ONE analyzes some of the oldest human remains ever found on the Italian Peninsula. The teeth, which are some 450,000 years old, have some telltale features of the Neanderthal lineage of ancient humans. Dating back to the Middle Pleistocene, the fossils help to fill in gaps in an intriguingly complex part of the hominid family tree.

The species Homo neanderthalensis shares an unknown common ancestor with our own species, Homo sapiens, but it’s unclear exactly when the lineages diverged. Homo sapiens evolved perhaps 300,000 years ago, according to the fossil record, while Neanderthals’ evolutionary timeline has proven even trickier to pin down. Some genetic studies suggest that their lineage split from our own as long as 650,000 years ago, but the oldest definitive fossil evidence for Neanderthals extends back only about 400,000 years.

To help to take a bite out of that gap, Clément Zanolli of the Université Toulouse III and colleagues used detailed morphological analyses and micro-CT scanning techniques to painstakingly measure the 450,000-year-old teeth. The teeth were then compared, inside and out, to those of other ancient human species, revealing that they have Neanderthal-like features.

“With this work and other recent studies, it seems now evident that the Neanderthal lineage dates back to at least 450,000 years ago and maybe more,” Zanolli says in an email. “This age is much older than the typical Neanderthals, and before our study it was unclear to which human fossil species these Italian remains were related.”

 

Neanderthal Teeth Rendering

A virtual rendering of the Visogliano and Fontana Ranuccio teeth. 

Most Neanderthal fossils are far more recent, dating from about 130,000 to 40,000 years ago, making evidence of the species’ earlier period hard to come by. The Middle Pleistocene Era teeth were found at two different sites, one near Rome (Fontana Ranuccio) and another outside Trieste (Visogliano). Together, these tiny fossils represent an intriguing piece of physical evidence that supports the findings of genetic studies of ancient human ancestry.

“I think that this is an interesting study, demonstrating that many of the features of Neanderthal teeth are present in Europe as far back as 450,000 years ago, which is farther back in time than Neanderthals have yet been identified in the fossil record,” says Ohio State University anthropologist Debbie Guatelli-Steinberg in an email, who wasn’t involved in the study. “This pushes back the ‘hard evidence’ of the split of Neanderthals from modern humans and is entirely consistent with the divergence dates coming from ancient DNA analyses, which suggest that the divergence occurred before 450,000 years ago.”

But the story isn’t as simple as a fork between modern human and Neanderthal lineages. Rather, the ancestral tree of the genus Homo appears wonderfully complex.

“There are other European fossils of comparable age that lack the Neanderthal features of these Italian fossils, and therefore indicate that other kinds of humans, besides Neanderthals, may have been present in Europe during this period of time,” Guatelli-Steinberg says.

One species in particular, Homo heidelbergensis, has been suggested as the possible common ancestor of both Neanderthals and modern humans.

“During the Middle Pleistocene, another species called Homo heidelbergensis was present in Europe, and its relationships either with Neanderthals or with more archaic species like Homo erectus are still unclear,” Zanolli says.

As scientists further untangle the evolutionary pathways of ancient humans, teeth will likely continue to play a critical role. Made of enamel, the body’s hardest biological substance, teeth tend to survive longer than bone. Additionally, the shapes and structures of teeth provide a valuable diagnostic tool to discriminate between our various ancient hominin relatives.

But how does one tell a Neanderthal’s tooth from a modern human’s, or any of the lineages in between? Paleoanthropologist Kristin Krueger of Loyola University of Chicago says that in general, teeth and jaws get smaller as evolution progresses, likely due to dietary changes such as the development of cooking. But when it comes to teeth, size isn’t the only thing that matters.

Cusps, crenulations, ridges and other features can be used to categorize the teeth of early humans. Tooth interiors can differ as well, and variations like enamel thickness and pulp chamber size can yield critical information to the trained eye.

“This study is an excellent example of what we can learn about evolution from teeth in general, and also what we can learn without destructive analysis,” Krueger says in an email. “The dental record from this time period and location is rare, so to have the number of teeth and analyze them to this degree without having to cross-section them or do destructive analysis (which is necessary for DNA analysis) is of paramount importance.”

And teeth can potentially do much more than simply uncover the roots of our evolutionary family tree. Ancient chompers can often teach us about the lives and diets of the ancient humans they belonged to.

“We think of teeth and dental records when identifying a random body in the woods, but what we don’t often appreciate is the scope of information that teeth can reveal. They are like little windows into a person’s life and can tell us about things like age, diet, hygiene, migration patterns, weaning practices, stress episodes and more,” Krueger says.

That such information might endure for half a million years makes the humble tooth an important tool for untangling the complex threads of early human origins.

An Entire Frog Species Was Almost Wiped Out by a Deadly Fungus, But Then They Evolved


We’re witnessing evolution happen in front of our eyes, and it’s incredible.

Within a decade of a massive die off due to a fungus commonly known as chytrid, the frog species left in El Copé, Panama developed the ability to coexist with the deadly fungus.

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In a later field study, the researchers found that frogs infected with the fungus survived at a nearly identical rate compared with uninfected frogs.

In 2004, the frogs of El Copé, Panama, began dying by the thousands. The culprit: Batrachochytrium dendrobatidis. Within months, roughly half of the frog species native to the area went locally extinct.

What happened?

New research, which appears in Ecological Applications, suggests that the frogs underwent ecological and/or evolutionary changes that enabled the community as a whole to persist, despite severe species losses.

The results could mean good news for other hotspots of amphibian biodiversity hit hard by the chytrid fungus, such as South America and Australia, researchers say.

“Our results are really promising because they lead us to conclude that the El Copé frog community is stabilizing and not drifting to extinction,” says lead author Graziella DiRenzo, a postdoctoral researcher at Michigan State University.

“That’s a big concern with chytrid worldwide. Before this study, we didn’t know a lot about the communities that remain after an outbreak,” DiRenzo says.

DiRenzo and her colleagues returned to the same small, two-square-kilometer field site in El Copé every year from 2010 to 2014.

They broke the field site down into smaller, 20-meter subsites, repeatedly sampling the subsites several days in a row within a season. Each time, the researchers tested individual frogs for the presence of the fungus while assessing the severity of any disease symptoms.

The researchers then developed a novel model to assess disease dynamics in communities beset by an outbreak. The frequent, repeated sampling of frogs in the field allowed the team to minimize biases in the model and enabled the researchers to conclude that infected frogs were surviving at the same rate as uninfected frogs.

This surprising result strongly suggested that the frog species remaining in El Copé developed the ability to tolerate the fungus and survive its deadly effects.

“Our statistical model allowed us to estimate amphibian survival and disease dynamics in a case where the small size of the remaining amphibian community prohibits the use of more traditional analysis methods,” says coauthor Elise Zipkin, an assistant professor in the integrative biology department.

“This new modeling framework offers unprecedented opportunities to examine the factors impacting small and declining populations decimated by disease.”

‘Eco-evolutionary rescue’

The researchers suggest that the El Copé frog community stabilized through an effect known as “eco-evolutionary rescue.”

In this scenario, some species may have evolved tolerance to the fungus while other highly infectious species died off and stopped contributing to the spread of the pathogen.

The fungus itself may have also become less virulent and the frog community as a whole may have undergone other types of restructuring.

The researchers note that, because researchers had studied the frog community in El Copé for years before the 2004 outbreak, the research site provides a rare window to assess changes to a frog community as a result of widespread chytrid infection.

If the community has stabilized here, the researchers say, it is likely that other hard-hit frog communities elsewhere in the world may have undergone similar adaptations—even where disease has reduced the overall number of species and/or individuals.

“The frogs of El Copé are not doing great, but they’re hanging on. The fact that some species survived is the most important thing,” says coauthor Karen Lips, a biology professor at the University of Maryland.

“If enough frog species in a given place can survive and persist, then hopefully someday a vibrant new frog community will replace what was lost.”

Evolution Saves Species From ‘Kill the Winner’ Disasters


Modelers find evidence that a combination of competition, predation and evolution will push ecosystems toward species diversity anywhere in the universe.
 

Ecologists have puzzled over how the various plankton that compete for the same resources in marine ecosystems can have such enduring diversity.

At a meeting of the American Society of Naturalists in 1960, the noted British ecologist G. Evelyn Hutchinson posed what he called “the paradox of the plankton.” Look at a flask of seawater; it will be filled with diverse species of plankton, all competing for the same vital elements and nutrients. Yet natural selection implies that over time, only one species should occupy an ecological niche, a concept known as competitive exclusion. And what is true of plankton seems to be true of many protozoa, plants, birds, fish and other organisms, too. How can ecosystems routinely have so many competing species that stably coexist?

Ecologists have mulled over this vexing paradox ever since, but they have generally taken comfort in a solution known as the “kill the winner” (KTW) hypothesis. It hinges on the predator-prey relationships in ecosystems, which are often species specific. As one species starts forcing out its competitors, its rising population allows more of its predators to prosper, too. Predation eventually pushes the number of prey back down again (hence, kill the winners). The combination of competition and predation then lets several populations of rival species coexist in equilibrium. The KTW hypothesis became many ecologists’ go-to explanation for biodiversity.

When Nigel Goldenfeld, the director of the NASA Astrobiology Institute for Universal Biology, and Chi Xue, a graduate student in his laboratory at the Carl R. Woese Institute for Genomic Biology, started looking more closely at the KTW idea in 2015, they didn’t intend to blow it up. Rather, they were exploring what features of life and ecosystems might be ubiquitous throughout the cosmos. Diversity seemed like a good candidate. “If you look at different isolated ecosystems on Earth, you see diversity everywhere,” Xue said. They were curious about what might create and sustain that diversity, and whether it might be as relevant on another planet.

But they noticed an unrealistic defect in the calculations that had traditionally been used in models to validate the KTW idea: They “described populations as if individuals did not exist. It’s as if we described a liquid without acknowledging atoms,” Goldenfeld explained by email. Because those models allowed populations to rebound even after plummeting to mere fractions of individuals, they underestimated the amount of extinction that could occur. (Goldenfeld and Xue refer to this problem as a lack of “stochastic noise” because the calculations do not reflect the mathematically arbitrary discontinuities that the real world’s limitations impose.)

Xue and Goldenfeld decided to redo the models more realistically. “We didn’t expect the KTW idea to fail,” Xue said. “We just wanted to see if there would be anything different if we added the noise.”

The results, which they recently described in Physical Review Letters, were catastrophic. Biodiversity and species coexistence didn’t just drop; they disappeared. “Basically, every species went to extinction,” Xue said. In repeated trials, fluctuating prey populations kept dropping to zero, and then their predators went extinct from lack of food. Sometimes the system devolved to a single pair of predator and prey species that persisted, but even those arrangements were not always stable. The kind of species-rich diversity found in nature was nowhere to be seen.

GRAPHIC: EXPLAINER OF ORIGINAL KILL THE WINNER

 

But Xue and Goldenfeld then went a step further to include something else that earlier simulations had left out: evolution. They allowed prey species to get better at evading predators, and predators to get better at catching prey.

What followed was an arms race, as the escalating capabilities of the prey and the predators evolved in parallel, and it made all the difference. That competition added more species diversity to the system while the KTW effects kept any one species from taking over. Biodiversity in the simulations flourished.

Xue and Goldenfeld see evidence from genomics that this coevolving dynamic occurs in nature, too. “When you look at bacteria and find the regions of the genome that are evolving faster, those are the regions involved with viral resistance,” Xue said. As their coevolving KTW model suggests, selection pressure to resist viruses seems to exceed other pressures — for example, to compete better against other bacteria.

GRAPHIC: EXPLAINER OF COEVOLVING KILL THE WINNER

Lucy Reading-Ikkanda/Quanta Magazine

Still, that’s not conclusive proof, and the researchers plan to investigate further how generalizable their conclusions are. They want to see what happens when predators are less specific about their prey. Another consideration, according to Goldenfeld, is that in addition to killing bacteria and other cells, viruses sometimes swap genes among them. This dual role — “as predator and also taxi driver for genes,” he said — can have profound effects on the evolution and stability of ecosystems.

It’s also uncertain whether the coevolving KTW model applies equally well to all types of life. “In principle, this interaction between predator and prey isn’t specific to microorganisms. It’s everywhere, like between the hare and fox,” Xue said. But she also noted that their model assumes that evolutionary changes (like mutations) and ecological changes (like the birth and death of organisms) happen on the same timescale and with about the same frequency. “That’s not really the case for species like the fox and hare, but that’s common in microorganisms.”

According to Jed Fuhrman, a professor of biological sciences at the University of Southern California, modeling approaches can generally be useful but should be interpreted cautiously. “Some assumptions and aspects are more directly applicable to complex natural systems than others.” Because even microbial communities employ a variety of survival strategies, he said, “models may apply to a portion of the community more than to others.”

But if the coevolving KTW model does prove to be broadly applicable, then according to Goldenfeld, it shows that “there are very generic ways to get diverse populations in an ecosystem and that monocultures are the exception, not the rule.” Wherever life evolves, even on other planets and moons, we should expect it to diversify into complex ecosystems. He said that one future direction for his lab’s work will be on “how a community metabolism emerges” from diverse organisms, each processing materials in their shared environment in different ways.

That idea could be relevant to space scientists, for example, when they send future probes to seek signs of life in the oceans under the ice covering Jupiter’s moon Europa and Saturn’s moon Enceladus. If life is there, they should probably expect to see the biochemical signatures of an entire ecosystem, not single organisms.

According to Kevin Peter Hand, a deputy project scientist for NASA’s Jet Propulsion Laboratory, the instrumentation being developed for probes to Mars, Europa, Enceladus and other suspected havens for life already look for signs broadly associated with ecosystems. He said that the proposed Europa Lander mission concept on which he is working is designed to capture “at least nine different, highly complementary measurements that are agnostic to individual biological species,” such as the complexity and chirality of any organic compounds and the presence of cell-like structures in samples.

But if astrobiologists ever get to move past the problem of whether life exists and can progress to examining how closely the dynamics of alien ecosystems resemble those of Earth, then knowing a solution to the paradox of the plankton may be critical.

Your Ancestors Didn’t Sleep the Way You Do


Nobody questions the importance of getting enough sleep. At minimum, it’s essential for rejuvenating the mind and revitalizing the body. But, what is enough? And what does it look like? Many people find they wake during the night and wonder if they’re suffering from a sleep disorder or other health issue. While that could be totally possible, it’s also possible that sleep may not be an all-night thing. In fact, historical records, centuries-old literature, and ancient references to sleep are all revealing a whole new way we should be looking at how we slumber.

Segmented Sleep: More Normal Than You Realize

If waking up during the night is a frequent “problem” for you, you might wonder if you’re suffering from insomnia or sleep apnea. “Segmented sleep” is a seemingly irregular sleep pattern that may not be a disorder at all, but a natural biological response that we, in modern times, have forgotten.

English scholar Roger Ekirch cemented the idea that our ancestors used to naturally practice segmented sleep, using their middle-of-the-night waking hours to pray, meditate, create, or finish chores around the home. [1] Roger Ekirch found references to “first sleep” and “second sleep” in literature, legal documents, and even letters written before the Industrial Revolution.

Many who practice segmented sleep find the in-between hour or hours to be one of the most relaxing periods. This may be because this middle period between first sleep and second sleep is around midnight where the brain produces prolactin, a hormone that supports a feeling of relaxation.

Before Reaching for That Sleeping Pill, Consider This

Our natural biorhythms are governed by exposure to light and darkness. Before the introduction of the light bulb, almost everyone scheduled their day around the rising and setting of the sun. When the sun rose in the morning, so did humans, and when the sun hit the horizon in the evening, we more than likely went to sleep around the same time.

Our brain produces serotonin in response to sunlight, and this neurotransmitter provides an energetic, wakeful feeling.[2] In contrast, when we’re exposed to darkness – meaning no artificial light whatsoever – our brain produces sleep-regulating melatonin. Computers, television screens, smartphones, tablets, and every other source of light in the evening hours is artificially extending our waking hours and interfering with our neurochemistry.

Also see: The Dark Side of Blue Light — How Tablets, Computers and Smartphones are Making Us Fat, Sick and Stupid

Because of this, it is possible that the practice of segmented sleep naturally fell away from public knowledge. We stay up longer, produce serotonin when we’re not supposed to, and eat less-than-ideal food — all of which could be the reason why we usually sleep throughout the night without waking and view this as normal. Even most medical professionals and sleep specialists have never heard of segmented sleep and aren’t trained to handle this natural occurrence.

So if this is happening to you, do a little more research into segmented sleep and its possible benefits before you reach for a sleeping pill. You may be more in tune with your ancestral rhythms than most people.

Do you wake up in the middle of the night? What do you do during that time? We’d love to hear your thoughts and insight!

References:

  1. A. Roger Ekirch. Sleep We Have Lost: Pre-Industrial Slumber in the British Isles. Am Hist Rev. 2001;106(2):343-86.
  2. Simon N. Young. How to increase serotonin in the human brain without drugs. J Psychiatry Neurosci. 2007 Nov; 32(6): 394-399.
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