A wasp with virus DNA sounds like  the fever dream of a supervillain – a mash-up of two organisms that most  of us would rather not encounter.

But evolution doesn’t care about your  feelings and natural selection is going   to favor bizarre team-ups, if there’s  a reproductive advantage at stake. In this case, that means there’s a wasp  family out there whose livelihood is   so intertwined with the survival of a  virus that they partly share a genome.

And ironically, this extreme teamwork is  all for the sake of being better parasites. [♪♪ INTRO ♪♪] The Bizarre Beasts pin club is open  for subscriptions for the whole month! Sign up by March 20th and the first pin you'll  get will be one of these weird little wasps. Mutualism, a symbiotic relationship  where both species benefit,   is one of the coolest interactions in nature.

Whether it’s dental work in exchange for a meal,   or someone to keep an extra eye out while you  both forage, cooperation can be awfully nice. And then, way at the other end of the  symbiotic spectrum from mutualism,   you’ll find parasitism, where one organism’s  success usually comes at a host’s expense. But there’s also a version  of this called parasitoidism.

A parasite’s host is harmed, sure, but  it typically isn’t outright killed. A parasitoid, on the other hand,   basically uses its host as a dual-purpose  incubator and buffet for its young. And the wasp family Braconidae is  all about that parasitoid lifestyle.

Braconidae is the second largest family of  wasps, with over 17,000 recorded species   out of an estimated 32,000 to 42,000 total,  and they can be found all over the world. Wasps in this family are mostly solitary, and  relatively small, typically maxing out at 1.5 cm. This makes them pretty unassuming,  especially for a wasp – instead of a big, angry swarm,  adults are just these cute, little   solo guys who fly around drinking nectar.

It’s during reproduction that things get weird: braconids lay their eggs on or  inject them into an insect host,   which the larvae then devour, from  the outside in or from the inside out. Most braconids parasitize caterpillars, but  some species target other insect hosts, as well. After the wasp larvae eat their fill of  their unlucky living nursery, they pupate, often right on the host’s corpse, and then emerge as adults.

But as fascinatingly horrifying  as a parasitoid life cycle may be,   it isn’t the symbiotic relationship  we really care about in this episode... What about those viruses we mentioned earlier?? Well, parasitoid wasps have  to do all kinds of strange   stuff to get away with their invasive  egg-laying, starting with using venom.

Stingers are, after all, a modified  version of the organ wasps use to   lay eggs, called an ovipositor,  so they can serve both purposes. Wasps that lay their eggs on the outside  of a host use their venom to slow it down   or get it to hold still, either  long enough for the egg-laying   process or for the entire  development of their offspring. But species that lay their eggs inside  the host have even bigger obstacles.

Insects tend not to be super interested  in being slowly consumed from the inside,   so their immune systems fight  back against these wasp invaders. And chemical compounds in the wasps’ venom have   often specifically adapted  to counter these defenses. But in addition to venom, several subfamilies  of braconids also inject viruses when   laying their eggs, and the viruses play the key  role in stopping the host’s immune response.

And, if that wasn’t bizarre enough, these  braconids actually make the viruses they   inject in their own bodies, using virus  DNA that’s fully integrated into their own. The wasps are literally manufacturing  whole viruses for their own use. Instead of the virus replicating  itself, the wasps are doing it for them.

And the way that works is: scattered throughout  the DNA of these wasps are the genes for   assembling virus protein shells, separated  from the viral genes that go inside them. Cells in a special compartment of  the female wasp’s ovaries express   the genes for making the virus protein shells,   producing the empty containers that  will hold the DNA for infectiousness. These wasp cells also copy the genes  for acting like a virus and then store   those copies as little DNA rings  inside the viral protein cases.

In a normal virus, these steps  would all be done by the virus… but in this case, the wasps are the  biological copy machine making both   the inside and outside of the virus,  then stapling those two together. This process destroys the specialized  cells, but releases a high concentration   of newly-minted viruses into the wasp’s  oviduct, which can then be injected,   along with venom and an egg or two,  into an unsuspecting caterpillar. Then, the viruses run interference on the  insect equivalent of white blood cells,   keeping them from encapsulating the wasp eggs.

And eventually, the larvae hatch and grow,  uninterrupted by pesky bodily defenses. These wasp-made viruses have the basic  characteristics of a typical virus, they infect host immune cells and contain  the genetic tools to disable those cells – but they don’t have the ability  to make more of themselves. The genes for that are kept  exclusively by the wasps.

And, yes, all of that is as  incredibly bizarre as it sounds… so, how did it evolve? Viruses make evolution  extra-interesting in two ways: they evolve quickly, and  they’re just weird overall. They replicate much faster  than most other organisms,   so mutations can lead to big adaptive  changes in relatively little time, which is made even easier  by how simple viruses are.

They’re effectively just genes  in a protein carrying case.  That to-go box of DNA or RNA contains the  instructions to make copies of itself,   and to do so by any means necessary, because viruses don’t actually have any of the   tools or raw materials to  replicate, just the manual. Instead, they hijack living cells and  forcibly turn them into virus factories,   using up the cells’ resources from the inside  until they die and release all the virus copies. In other words, parasitoidism  on a much tinier scale.

The viruses associated with wasps  are a group called polydnaviruses,   and their entire genome is  inside the wasps’ genome, the virus only exists when a  wasp expresses the viral genes. But harboring secret virus DNA is a  lot more common than you might think: 8% of our genome is left over from old viruses,   and as much as 40% on top of that  might also have similar origins. The ancestors of all living things got  sick at some point in evolutionary history,   and when viruses are the culprits,  their unique nature can leave a mark.

In certain cases, after infecting a cell, a  virus may incorporate its genes into those of   the host cell without immediately  switching on the “copy” function. Sometimes the cell just dies, sometimes it  slowly puts out a small but steady supply of   infectious virus copies, sometimes it starts  dividing out of control and forms tumors, and sometimes that virus DNA stays  put without actually doing anything. Host cells are constantly fighting all of  the nastier of these potential outcomes,   while viruses are driven by selective  pressure toward workarounds.

So when viruses succeed in both sticking  around in a long-term capacity and   successfully pulling the cellular levers, this  can actually lead to both parties benefitting. Sometimes it’s as simple as the virus’ own tools  helping the host fight off other viral infections. Or it can go the direction of wasp polydnaviruses.

They’re believed to have evolved from a  group of viruses that sometimes target   insect reproductive systems using  very similar tools to the ones that   braconids’ little helpers use on  caterpillar immune cells today. So wasp genetic repair mechanisms and other tools  in the arms race against viral infection may have   led to braconids’ ancestors dispersing  the virus genes across their own genomes. By separating the genes for doing infectious  virus stuff from the genes for actually   building more virus proteins, the wasps  essentially “domesticated” the virus.

It can’t infect the wasps if  it can’t spread for itself. In turn, the virus’ pathogenic tendencies,  when turned on the wasps’ hosts, proved to   be a major selective advantage, so  the partnership became locked in. Cooler still, the viruses now even seem  to have some wasp genes mixed into their   immune-suppression toolkit for good measure.

There’s no virus without the wasp, and  no wasp babies without protection from   the virus, meaning some truly baked-in mutualism… Mutualism of one parasitoid inside another,  in turn working together in a shared host. Think of it as a “game recognizes  game” turducken of parasitism. Evolution favors survival and  reproductive strategies that   just work, no matter how bizarre  or convoluted they might seem.

In that context, parasitism makes sense, it’s certainly easier to survive by  letting a host do all the heavy lifting! This helps explain why parasitism has  evolved more often than any other life   history strategy, and why parasites make  up around half of all known species. A relationship as complex as the one  between today’s beasts and polydnaviruses   may sound unlikely at first blush, but  it ticks that basic evolutionary box of “yep, that technically works.” With so many parasites around, some  were /bound/ to join forces eventually.

And tiny invaders gaining crucial functions  inside of cells is a tale as old as time. Just ask your mitochondria! Sign up for the pin club at BizarreBeastsShow.com  and help keep this channel going.

If you want a wasp to be your  first pin, sign up by March 20th. Are there Bizarre Beasts pins  that you missed the first time around? Well, every now and then we double  check our inventory and find that   we have a few pins left from episodes in the past.

You can check out BizarreBeastsShow.com  for these past pins. We might just have the ones you're missing. And now, for some bonus facts… [♪♪ BONUS FACTS ♪♪] Braconids aren’t the only wasps known  for eating their childhood home to death.

There’s also Ichneumonidae, the most  diverse family of wasps on the planet,   and they have their very own viral assistants for  their parasitoid endeavors, in two subfamilies. This is interesting because there  are two main types of polydnavirus, bracoviruses and ichnoviruses, each corresponding to the wasp  family they’re named after,   and each with their own distinct physical  structure and evolutionary origin. That is, braconids and their  bracoviruses evolved independently from, and convergently with,  ichneumonids and their ichnoviruses.

The latter share plenty of similarities  with the braconid-bracovirus setup: a bunch of genes for host immune  suppression that seem to largely   come from wasps and genes for making  the protein capsule nowhere nearby,   balanced out by virus protein  structures that are very different. But ichneumonids arrived at  this completely separately   from the beasts we already discussed today, so as rare as this mutualism may be in  nature, it also managed to fully evolve twice. Studies on this wasp family are still pretty  new compared to those with Braconidae,   so it’s likely that we’ll discover many more  wasp species with this amazing adaptation.

But no matter how many instances we find,  it’s still going to be pretty bizarre. [♪♪ OUTRO ♪♪]