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This week, definitive evidence that wasps were just as brutal millions of years ago as they are today, and some interesting effects caused by naked mole-rat poop.

Hosted by: Stefan Chin

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Sources:

https://www.nature.com/articles/s41467-018-05654-y
http://www.pnas.org/content/early/2018/08/21/1720530115
https://www.nytimes.com/2018/08/28/science/wasps-parasites-fossils.html
http://www.bbc.com/earth/story/20150522-the-wasps-that-rule-the-world
[ INTRO ].

Many wasps are brutal assassins, taking over the bodies of unsuspecting insects and killing them from the inside out. And last week, in the journal Nature Communications, German researchers reported the first clear evidence that they’ve been doing this for over 30 million years. There are hundreds of thousands of parasitic wasp species, and all have a rather macabre start to life. While adults look and act like wasps, their young are terrifying parasites.

Female wasps lay their eggs on or in a suitable host. The larvae that hatch slowly consume that host from the inside as they develop. Then, they either eat their way out, or just pupate right there in the hollowed-out shell that remains.

And it’s that whole living-inside-another’s-body thing that makes fossils of these wasps so hard to find. Before this study, paleontologists only had a few adult wasps and some larvae trapped in amber, which isn’t much to go on if you want to deduce what parasitic wasps were like in the past. But recent advances in scanning technologies have finally made it possible to peer inside a fossil without destroying it.

So to look for ancient parasitic wasps, the researchers examined 1,510 mineralized fly pupae which were excavated from a fossil bed in France. According to previous studies on fossils from the same area, these pupae are thought to be about 30 to 40 million years old. And from the outside, it was impossible to tell if any contained parasites.

So the team used a new kind of x-ray scanning technology to construct high-resolution 3-dimensional images of the fossils. And they discovered that 55 of them were parasitized by wasps. Many of the wasps were in the final stages of pupation, and 20 appeared to have recently hatched.

Some were so well-preserved that the researchers could see hairs on the wasps’ backs or determine if their wings were folded or outstretched. And based on physical features, these now-extinct wasps could be split into 4 new species, three of which looked so distinctive they were put into new genera. One of those new genera was named Xenomorphia —a nod to the chest-bursters from Ridley Scott's “Alien” franchise.

These are the most intricate parasitic wasp fossils to date and the first definitive ones of them inside their hosts, so they’re already providing scientists with novel insights into ancient wasp ecology and evolution. And the researchers hope their success will inspire similar studies, as there are bound to be a lot more ancient parasites hiding inside otherwise unremarkable fossils. Last week, a study in the journal Proceedings of the National Academy of Sciences found a hormone that seems to compel naked mole-rats to care for other mole-rats’ babies.

But it was how this hormone makes its way into them that stood out: they get it by eating the mother mole-rat’s poop. Naked mole-rat colonies are eusocial. This means that a single female—the queen— reproduces while the other colony members or subordinates take care of her pups.

But they’re not always eager babysitters. Researchers from Azabu University in Japan found that subordinates can sometimes be slow to respond to the sounds made by pups. They’re most responsive during the queen’s postpartum period— the time just after she gives birth.

And blood tests revealed that this coincides with an increase in estradiol— a kind of estrogen hormone that’s been linked to parenting behaviors in other mammals. The only weird thing is that subordinates aren’t sexually mature, and they can’t make sex hormones like estradiol on their own. So it wasn’t clear where the estradiol was coming from.

There was one possible source. During that postpartum period, subordinates consume a lot of their queen’s feces. That isn’t as weird as it might sound— lots of animals do it to get a boost of nutrition from partially-digested material.

But feces can also contain hormones, so the researchers wondered if the poop-eating and the blood estradiol levels were connected. They discovered that the feces of pregnant mole-rat queens do contain a lot of estradiol. But to really test the connection, they added the hormone to feces from nonpregnant queens, and fed those feces to female subordinates for nine days.

Sure enough, their blood estradiol levels rose. And they were more responsive to the cries of pups than subordinates that ate unaltered feces. So the researchers concluded mole-rats’ parenting behaviors are directly induced by the hormonal supplement they receive through eating their queen’s poop.

It’s not all that surprising that mole-rat queens are able to steer their subordinates’ behavior. Queens from other eusocial species like bees also have ways to keep their colony members in line. But that usually means excreting pheromones which travel through the air.

It’s likely naked mole-rats can’t rely on pheromones because the part of their olfactory system that detects them is poorly developed. So, apparently, they influence others using their poop instead. The next step is to understand exactly how the hormone works, so the researchers are planning to examine the brains of the mole-rats to understand what neural changes underlie this seemingly gross yet advantageous social behavior.

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