Small Spiders’ Brains Fill Up Most of Their Body Cavity

If spiders weren’t creepy enough… It turns out that the smaller a spider is, the larger its brain is in proportion to its body size. This is how a tiny spider and a huge spider can have equally complex behaviour. What this means anatomically is that in some spiders, the central nervous system takes up as much as 80% of the body cavity, with their brains literally spilling into their legs. 

More from National Geographic:

Taking up so much body space for a brain would seem to be a problem for a spider’s other organs, Eberhard said. “But [that aspect] hasn’t really been studied.”

Just by the way the spiders look, though, it would make sense that the arachnids are trading something for their big brains.

For instance, in the jumping spider Phidippus clarus, which the researchers examined in a separate study, the adult’s digestive system is in the spider’s cephalothorax—its head and body cavity.

But “in the young one, all that stuff is filled up with brain,” and the baby spider has a less developed digestive system. It’s still unclear, though, what impact this has on the developing spiders…

Presumably, large brains are necessary to spin webs, a behavior thought to be more complex that, say, “a larval beetle that simply eats its way through the fungus where it lives,” Eberhard wrote in an article describing the research…

It’s a weird concept, having so much of a body filled up with the central nervous system (brain and spinal cord). I wonder how or if it relates to spiders’ reaction times, if their sensory organs (including skin) are so very close to their central nervous system. Is there a difference in reflexes between small and large spiders, or young and adult, attributable to relative brain size? Maybe we’ll find out in the future!


Blinking Bacteria As Biological Sensors

You’re probably aware that making lab organisms – or at least parts of them – glow a certain colour is relatively commonplace. Biologists frequently attach the gene for green fluorescent protein (GFP) or its differently coloured family members to a gene that they’re interested in, so whenever the gene of interest is activated GFP is produced and the relevant target fluoresces, a nice visible marker. 

In the last few years a group of researchers found a way of tying fluorescence to the cycle of bacteria’s biological clocks, producing rhythmic blinking. Last year they managed to coordinate this blinking in large groups of bacteria, which they compare to living neon signs. Now, they’ve shown that this system can be used as a living sensor for environmental pollutants.

From ScienceDaily:

Using the same method to create the flashing signs, the researchers engineered a simple bacterial sensor capable of detecting low levels of arsenic. In this biological sensor, decreases in the frequency of the oscillations of the cells’ blinking pattern indicate the presence and amount of the arsenic poison.

Because bacteria are sensitive to many kinds of environmental pollutants and organisms, the scientists believe this approach could also be used to design low cost bacterial biosensors capable of detecting an array of heavy metal pollutants and disease-causing organisms. And because the sensor is composed of living organisms, it can respond to changes in the presence or amount of the toxins over time unlike many chemical sensors.

“These kinds of living sensors are intriguing as they can serve to continuously monitor a given sample over long periods of time, whereas most detection kits are used for a one-time measurement,” said Jeff Hasty, a professor of biology and bioengineering at UC San Diego who headed the research team in the university’s Division of Biological Sciences and BioCircuits Institute. “Because the bacteria respond in different ways to different concentrations by varying the frequency of their blinking pattern, they can provide a continual update on how dangerous a toxin or pathogen is at any one time.”

They go on to explain that there are too many bacteria on their “microfluidic chips” (up to 60 million cells) for the bacteria to all coordinate in their usual way, which is called quorum sensing (roughly, relaying signaling molecules between them). They found, though, that colonies released gases that could be used to coordinate between them, while cells within colonies still coordinated by quorum sensing.

This is a pretty interesting idea. I trust biologists to be able to make bacteria sensitive to various molecules and react in various ways; I see no reason why bacteria wouldn’t be able to glow different colours based on the environment, for example. There may be more possibilities with living versus non-living sensors simply because of the incredible complexity of living things, which we can take advantage of without reconstructing from the ground up.

Watching New Species Emerge

Science Sushi has a great article on new species evolving before our eyes. Evolution deniers may claim that we never see new species in the process of evolving, but that’s simply untrue, and further confirms that the political debate over evolution has nothing to do with science or facts.

Critics of evolution often fall back on the maxim that no one has ever seen one species split into two. While that’s clearly a straw man, because most speciation takes far longer than our lifespan to occur, it’s also not true. We have seen species split, and we continue to see species diverging every day.

For example, there were the two new species of American goatsbeards (or salsifies, genus Tragopogon) that sprung into existence in the past century. In the early 1900s, three species of these wildflowers – the western salsify (T. dubius), the meadow salsify (T. pratensis), and the oyster plant (T. porrifolius) – were introduced to the United States from Europe. As their populations expanded, the species interacted, often producing sterile hybrids. But by the 1950s, scientists realized that there were two new variations of goatsbeard growing. While they looked like hybrids, they weren’t sterile. They were perfectly capable of reproducing with their own kind but not with any of the original three species – the classic definition of a new species.

How did this happen? It turns out that the parental plants made mistakes when they created their gametes (analogous to our sperm and eggs). Instead of making gametes with only one copy of each chromosome, they created ones with two or more, a state called polyploidy. Two polyploid gametes from different species, each with double the genetic information they were supposed to have, fused, and created a tetraploid: a creature with 4 sets of chromosomes. Because of the difference in chromosome number, the tetraploid couldn’t mate with either of its parent species, but it wasn’t prevented from reproducing with fellow accidents…

The apple maggot fly, Rhagoletis pomonella is a prime example of a species just beginning to diverge. These flies are native to the United States, and up until the discovery of the Americas by Europeans, fed solely on hawthorns. But with the arrival of new people came a new potential food source to its habitat: apples. At first, the flies ignored the tasty treats. But over time, some flies realized they could eat the apples, too, and began switching trees. While alone this doesn’t explain why the flies would speciate, a curious quirk of their biology does: apple maggot flies mate on the tree they’re born on. As a few flies jumped trees, they cut themselves off from the rest of their species, even though they were but a few feet away. When geneticists took a closer look in the late 20th century, they found that the two types – those that feed on apples and those that feed on hawthorns – have different allele frequencies. Indeed, right under our noses, Rhagoletis pomonella began the long journey of speciation…

There are a few more really interesting examples and an explanation of how and why speciation can happen; you should check out the article at Science Sushi if you’re interested.

The point is that all kinds of creatures, from the smallest insects to the largest mammals, are undergoing speciation right now. We have watched species split, and we continue to see them diverge. Speciation is occurring all around us. Evolution didn’t just happen in the past; it’s happening right now, and will continue on long after we stop looking for it.

Fantastic. Evolution is not a thing of the past, and it doesn’t happen to some things and not others. I recently read someone’s racist theory about how because the modern human species began in Africa and went outwards, Africans were less evolved than others. That clearly doesn’t make any sense, and this article’s conclusion should make it obvious why (among other reasons): evolution doesn’t stop. Everything currently living is still evolving, and there’s no end goal to evolution that you can point at and say “The closer you are to that, the more evolved you are.” 

If anything, one might say that bacteria are the “most evolved” organisms, since they reproduce so quickly and thus can change their genetic makeup, as a community, far faster than most living things. Though they don’t have the benefit of sexual reproduction to shuffle around their genes, their DNA will still undergo mutation, and they can also exchange DNA with each other using conjugation

In conclusion, there’s a lot of misinformation about evolution, whether through ignorance or bad intentions. It’s too bad that more people don’t know more about it, because the truth of it all is pretty amazing. 

Velociraptors Hunting Like Birds

Not Exactly Rocket Science has an interesting article on the possible hunting patterns of some dinosaurs that had claws resembling the talons of big birds of prey. They may have used their claws to pin down their prey, as opposed to hacking and slashing. The article is definitely worth reading in its entirety, so go check it out if you can, but otherwise here are the highlights:

In [paleontologist Denver Fowler’s] vision, which he calls the “ripper” model, Deinonychus killed small and medium-sized prey in a similar style to a hawk or eagle dispatching on a rabbit. Deinonychus leapt onto its target and pinned it down with its full body weight. The large sickle-shaped claws dug into its victim, gripping tightly to prevent it from escaping. Then, Deinonychus leant down and tore into it with its jaws. The killer claws were neither knives nor climbing hooks; they were more like anchors.

It’s a simple idea, but a potentially important one, for it casts Deinonychus’s entire body into a new light. Fowler thinks that it flapped its large feathered arms to keep its balance while killing a struggling victim. And its feet, which were adapted for grasping prey, would have given its descendants the right shape for perching on branches. Fowler says, “It really helps to make sense of the weird anatomy of these little carnivorous dinosaurs.” …

This idea of Deinonychus sitting on top of small prey seems at odds with classic picture of this predator working in packs to bring down larger quarry. But again, modern birds show how the same grasping motions might have worked against big targets. Golden eagles can kill reindeer. They dig their talons deep into their victim’s back, holding on while the struggling reindeer widens its own wounds. Deinonychus might have used the same strategy to kill larger prey.

Tom Holtz Jr, who studies predatory dinosaurs, says, “Prey-riding is also common in the Galapagos hawk – there’s classic footage of them taking down marine iguanas much bigger than they are. They pin them down, and flap away as the iguanas take them for a ride.” Philip Currie from the University of Alberta also mentions the famous Mongolian “fighting dinosaurs” – a Velociraptor found in pitched battle with a Protoceratops. “It confirms that dromaeosaurids were seeking prey animals of their own approximate body size.” …

If Fowler is right, his model has important implications for the evolution of flight. The dromaeosaurids would have been very nearly ready for life in the trees. Their grasping feet, with opposable toes, could easily have adapted to grip branches as well as prey. Their flapping arms, used to balance themselves, could have adapted to help them fly. These animals were positively pre-adapted for life in the trees. Perhaps the graceful wings and perching feet of a blue tit got their start with bloody murder on the ground.

Proposing such a strong connection between dinosaurs and modern birds is pretty interesting; it’s useful to see how everything is related. Keep in mind though that at this point, this is only one person’s theory. 

Ants Release Airborne Poison to Paralyze Termites

Ants just got scarier. A certain type of African ant surrounds termites and sprays them with a toxin that eventually paralyzes them.

From Not Exactly Rocket Science:

C.striatula is a specialised termite-hunter. When it finds a termite, it raises its sting into the air, releasing chemicals that summon nearby nestmates. If the termite is a soldier, armed with powerful jaws, up to 15 ants can gather round. All of them stay a centimetre away from the termite, aiming their stings at it like fencers with swords outstretched. They close in, but they still never actually touch.

Termites don’t retreat – they defend their nests no matter the danger. That is a fatal mistake. After ten minutes of stand-off, the termite starts to shake. It rolls onto its back, with its legs batting the air in helpless convulsions. Within moments, it’s paralysed, and the ants finally move in and grab it.

C.striatula behaves in the same way when it finds other ants in its territory. These intruders have the good sense to flee, even if they’re much larger than C.striatula and even if they have the weight of numbers on their side.

It’s clear that the chemicals released from C.striatula’s sting do three things: they rally other workers; they repel other ants; and they paralyse termites…

Many animals have projectile weapons: some ants can spray formic acid; the  bombardier beetles squirt enemies with noxious burning chemicals; the spitting cobras spit venom; and both velvet worms and spitting spiders can spew immobilising glue.

In all these cases, there is an obvious and noticeable stream of liquid. By contrast, C.striatula’s long-range chemical weapon seems all the more sinister for its invisible nature. Only one other animal has something similar – another ant called Platythyrea conradti . It also raids termite nests. When it encounters a defending soldier, it drops into a crouch and opens its jaws. It never bites, and it doesn’t need to. Glands in its mouth release an airborne poison that paralyses the termites, in the same way that C.striatula does with its sting.

I’d love to see a video of this chemical warfare in action, but in lieu of that here’s a video from National Geographic showing an ant attack on a termite nest:

There’s a complex and fascinating world going on underneath us.

Archaeopteryx and On Classifying Species

There’s a fantastic article at 10,000 Birds about the classification of Archaeopteryx, usually considered the first species of bird to emerge from dinosaurs, and more generally how biologists figure out how to classify ancient species. It’s a pretty great and easy-to-read insight into how to figure out the evolutionary tree that we often take for granted. Check it out!

The Origin of Walking

From New Scientist:

A lungfish that uses its fins for walking could help to unravel the steps our distant relations took in order to move from water to land.

The African lungfish (Protopterus annectens) has lobe-shaped fins similar to those seen in the ancestors of the first vertebrates to walk on land.

Anecdotal evidence suggested that the fish use these to walk along lake beds. Now Heather King of the University of Chicago in Illinois has filmed the lungfish in motion and found that they do indeed walk using their two pelvic fins.

This suggests fins were used for walking before they evolved into specialised limbs, says King.

New Scientist has a video of this but it’s rather brief. This is pretty cool – an idea of one step in the path species took from single-celled aquatic organisms to land animals.

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