Sometimes there are things I simply can’t make work. I wish they would work. But they don’t.
For example, there are three articles this week—not one, but three—that include the term “Viviparous lizard.” Naturally, I immediately put all three on my must-write-up list. Not because they were super-duper game changing articles … but because I wanted to talk about the weird reproductive strategies of lizards.
Lizards make up the largest surviving order of reptiles. They’ve been around since at least the Middle Jurassic, when ur-geckos and proto-skinks show up. By the Cretaceous you start getting the first iguanas and monitor lizards. All of these guys were tromping the same forests and fernlands as the dinosaurs. You can’t even say that they were all “small and underfoot,” because Cretaceous lizards included the Mosasaurs, an ocean-going group that reached up into the medium-sized whale range. That thing that jumps out of the pool to clamp down on the “bad” dinosaur in Jurassic World? That wasn’t a dinosaur. Just a swimming member of the good old lizard family.
With more than 10,000 species, lizards are among the most diverse orders of vertebrates of any sort. And it shouldn’t be surprising that they’ve tried out a lot of different reproductive strategies. There’s a big variety of courting rituals, with males sometimes covering relatively enormous distances to seek out a mate. Quite a few throw off their brown or grey normal colors for near fluorescent greens and reds, or add a scattering of horns and frills and flaps for getting attention. There are some that get by entirely without males and maintain a double-set of genes that mix in their offspring rather than making each new baby a clone of mama.
And finally, there’s Zootoca vivipara, the Viviparous lizard. Zootoca lives in Europe and Asia, and it lives surprisingly far north. You can find it not just in the hills of Scotland, but in a band that includes much of Russia and both Sweden and Norway. Some marine turtles swim farther north, but that’s the only thing that keeps Zootoca from holding the Most Northerly Reptile award. What allows it to live so far north is that females have the ability to produce, not eggs, but live young.
Literally at the other end of the world, in Tasmania, there’s another lizard—the Southern grass skink—that shares this live-birth trick. And again, it allows the lizard to live in chilly, damp terrain that defeats other reptiles. These southern lizards develop complex placenta, genuinely feeding the young internally rather than just holding eggs inside the body.
Both kinds of lizards illustrate how live-birth can evolve in response to dealing with a harsh environment. The two lizards evolved this ability independently, and they’re far from the only reptiles to do so. Which is why I wanted to talk about them. But … I couldn’t really make the articles work for me. So we can’t talk about viviparous lizards.
So … moving on.
Immune cells use DNA as a snare
If you were to pull all the DNA out of a single human cell, it would make an impossibly thin, 6 foot long strand. That’s a nice abstract thought, but as it turns out there are practical implications: Such as the ability of some immune cells to literally use DNA strands as physical traps for bacteria.
Thirteen years ago, microscopy researcher Volker Brinkmann spotted a bizarre behavior while peering at immune cells called neutrophils to study how they killed bacteria. Like the quick flick of a frog’s tongue, neutrophils shot out strands of nuclear DNA to trap passing microbes.
They named these tossed out strands of DNA “neutrophil extracellular traps”—clearly so that they could abbreviate them as NETs. Since that initial research, scientists have not just found NETs in many different organisms, they’ve also found different kind of NETs.
However, they don’t yet agree on just how important this party trick is for the immune system. Is it a key feature and common approach, or just another in the many different ways that cells can take out surrounding invaders by committing cellular suicide? More than that, is this really something the cell is doing, or just something that happens when cells fall apart? Is it really a defense mechanism … or a happenstance?
The answer turns out to be … shrug. It may even be that these NETs are the cause of some diseases rather than the cure. Researchers are still at a point where they don’t know whether they want to make drugs that emulate the NETs or drugs that block the formation of NETs. There’s much more work to do here.
It’s the water special, shining damp on you, it’s the water special …
This week’s Proceedings of the National Academy of Sciences has a special focus on water. Cool, clear, water. There’s a cluster of ten papers, all of them focused on some aspect of the physics or chemistry of what, on Earth at least, seems like an utterly ubiquitous—and absolutely necessary—substance. This includes everything from a musing on how vital water is for life as we understand it, down to an article on the most efficient means of splitting water to create hydrogen fuel.
The nice thing about these papers is that they’re mostly written to be read by a larger audience than many of the things that appear in PNAS. Sure, self-healing catalysis may not be a topic you come across every day before lunch, but when you understand that it’s a way to making storing solar power more practical, it’s worth fighting through.
You can skim over all these water articles—and not get the least bit wet.
A close look at a 500 million year old eye
The introduction for this paper from a trio of European scientists makes a pretty bold claim about the eye under their microscope:
... it is probably the oldest record of a visual system that ever will be available.
But they could be right. The specimen is from an Early Cambrian trilobite, from shortly after that time when life “exploded” into astonishing level of variety—including every phylum that exists today and some that don’t. There are a lot of theories about why there the fossil record goes from sparse appearances by organisms that seem to be uniformly small or simple, to such a record of abundance. Maybe it was the more general appearance of hard parts that were more easily preserved. Maybe it was a period of relative ‘giantism’ for earlier forms that were so tiny they still escape notice. Maybe new forms of depredation led to an “arms race” that drove diversity. Maybe the explosion is an artifact of the few good fossil-bearing strata we have from around that time.
But in any case, one of the groups that appears in that big fossil boom is arthropods. And a lot of those arthropods are packing big, compound eyes—the kind you might see today on a dragonfly. So when the authors of this paper say they’ve got a look at what may be the oldest eye available, it at first seems ridiculous. There are thousands of great specimens of Early Cambrian organisms packing lovely, multi-faceted eyes. Only those specimens are pretty much casts of the outside of those eyes. What this team has is something else.
Until now, the fossil record has not been capable of revealing any details of the mechanisms of complex vision at the beginning of metazoan evolution. Here, we describe functional units, at a cellular level, of a compound eye from the base of the Cambrian, more than half a billion years old.
This eye was exquisitely preserved, in a way that reveals much of the internal structure.
In a phosphatized trilobite eye from the lower Cambrian of the Baltic, we found lithified remnants of cellular systems, typical of a modern focal apposition eye, similar to those of a bee or dragonfly.
But bees, dragonflies, and other insects are not descendants of trilobites. Eyes (like live-bearing reproductive systems) evolved independently at different times in many different parts of the animal kingdom—so they both groups may have developed similar eyes independently. But that’s probably not what we’re seeing here.
The presence of this very early, very insect-like eye suggests that eyes evolved first, in the arthropods that were ancestral to both trilobites and many modern orders.
Dry flies that nobody ties
And now an article that combines both insects and water. At Mono Lake in California, specialized flies dive down in the extremely alkaline, hypersaline waters of the lake to feed and lay their eggs. When they do, the flies … don’t get wet. A close examination shows that the fly moves in a tiny bubble of air, but not because the fly, like some diving spiders or insects, has captured some air to carry along.
Instead, minute changes in the physical and chemical structure of alkali flies makes them “superhydrophobic.” So water-repellent that they don’t get wet.
These diving flies are protected by an air bubble that forms around their superhydrophobic cuticle upon entering the lake.
The unique ability of these flies gives them a niche that’s unique to the lake and closely matched to both physical and chemical conditions found no where else.
However, while the ability of the flies to go in and out of the lake without getting wet seems semi-magical, there is a threat to this mystical trait—tourists in the lake. The same special properties that make the flies so resistant to water make them ‘sticky’ in contact with something that’s generally immiscible with water: The thin film of oils from suntan lotion left behind when visiting humans wade the salty waters can snare the flies.
Genetic variation not more evident for rich kids
A bi-coastal group of scientists tore through a set of Florida statistics looking for evidence that kids in wealthier families had more genetic variation in their cognitive abilities. That is: Were high-performing parents more likely to have high-performing kids when their families were wealthy, while people who were wealthy, but low-scoring on tests, showed similar results for their kids, because all those kids had more opportunity to live up to their potential. And the answer was … nope. Or at least, not in this study. Wealth and opportunity remain great predictors of performance. But there’s no evidence that you can better track some genetic component of cognitive skill by looking only at the top quintile.
Keeping ears CRISPR for longer
A group from Harvard Medical has managed to knock out a gene that causes progressive deafness in mice. Using the increasingly ubiquitous CRISPR-Cas9 toolset, they packaged genetic components inside of fatty lipids, and delivered this material to the inner ear. The treatment seemed to work in blocking the loss of the tiny inner-ear hairs critical to hearing.
The case here is a little specialized, because the gene that causes hearing loss in this condition comes in a damaged-undamaged pair. The CRISPR-delivered components were able to splice out the bad example, leaving the functional gene still functioning.
One big thing that makes this more important—the gene involved causes the same problem in humans as it does in mice. In fact, these mice are known as “Beethoven” mice.
Another day, another potential for miraculous cure via CRISPR.
Kids under stress make for adults who make bad decisions
Children who experience high levels of stress, tend to have tougher times making good decisions as adults. A study from the University of Wisconsin–Madison looked into this issue and found a physical issue behind the problem.
Individuals who experienced high levels of early life stress showed lower levels of brain activation when processing cues signaling potential loss and increased responsivity when actually experiencing losses.
This was a long term study, tracking the same group of kids over a decade. The team tested the kids at grade school age, made an evaluation of their home life and stress levels, then returned to the same people as young adults. The results seem to indicate that people who experienced high levels of early childhood stress were less likely to consider the potential risk of decisions, and took it harder when one of those risks occurred. So … possibly more likely to engage in risky behavior and less agile in rebounding from bad consequences.
The same couldn’t be said for people who were under high stress as adults—that didn’t reliably map to their decision-making skills. It was the conditions they experienced as children that left a lasting impression on how to evaluate risks and rewards.
Machine learning and the marketplace
We like to think we’re in the “information age,” but it’s clear we’re still on the boundary of changes that are going to destroy or irrevocably alter all the institutions that came from our industrial past. A pair of scientists from MIT took a look at what computers have already done to the workplace, and what’s left to come … and found we were a long way from done with the changes.
Digital computers have transformed work in almost every sector of the economy over the past several decades. We are now at the beginning of an even larger and more rapid transformation due to recent advances in machine learning (ML), which is capable of accelerating the pace of automation itself.
The big question they tried to address was just where machine learning would have maximum impact. It’s a very important question, because those parts that can’t be easily automated through machine learning are likely to be divided up between purpose-built “expert systems” and genuine human experts—making knowledge of the areas not easily reduced to machine learning highly valuable.
Machine learning is easily adapted to systems whose rules are well understood, for pulling easily recognized results out of large data sets, and for any task where the goal is unambiguous. As you would expect, this means it’s less suitable for situations where goals are rapidly changing, where processes are poorly understood, or where the results require specialized explanation.
The complete paper is available, and it’s well worth reading.
This week’s graphic comes from Andy Brunning at Compound Interest. Visit his site for a larger, easier to read version.
Happy holidays!