When infection is unavoidable, fruit flies ramp up recombination

So, you wanna head back to my place after this and make some recombinant offspring?

Imagine you find yourself in the midst of a large-scale epidemic, similar to the scenarios portrayed in movies like Contagion or Outbreak (or both!). The disease is extremely contagious, and the probability of becoming infected is high. Now imagine that scientists fail to discover a cure. There is no Dustin Hoffman-led team of military virologists available to develop a vaccine and save humanity, and the disease persists, with the potential to infect subsequent generations. In this harsh, disease-ridden environment, how could you ensure that your future offspring would survive?

It turns out, if you were a fruit fly, you might rely on recombination.

Disease is thought to have played a major role in shaping the reproductive strategies of animals. The Red Queen hypothesis predicts that species experiencing parasite-related selection pressures are more likely to evolve sexual reproduction, along with increased rates of outcrossing and recombination. This is because, in the ongoing evolutionary arms race between hosts and parasites, a little bit of genetic variation can make it a lot harder for the parasite to “win.”

But while strategies for increasing genetic variation may improve disease resistance, they often come at a cost. Increased recombination, in particular, can reduce fitness by breaking up locally adaptive combinations of alleles. One potential way to get around this issue is to increase recombination rates only when the risk of infection is high. However, we have yet to observe direct evidence of parasite-induced recombination in animals.

In a study recently published in Science, Singh et al. sought to investigate the capacity of fruit flies to plastically increase recombination in response to infection. To do this, the researchers infected Drosophila melanogaster females with a variety of parasites, and observed the proportion of recombinant offspring the females produced.

In order to track recombination events, researchers took advantage of the known genetic basis of two visible phenotypic traits. The ebony locus and the rough locus occupy nearby positions on the same chromosome in D. melanogaster, and recessive mutations at each of these loci have easily identifiable effects on the phenotype. For this study, the researchers generated females heterozygous at both ebony and rough.

Next, the researchers infected females with one of several different types of parasites. Two distinct (but similarly disturbing-sounding) methods were used to infect flies, depending on the type of parasite involved. In some trials, the researchers stabbed adult flies in the thorax with a needle covered in disease-causing bacteria. In other trials, the researchers housed larval flies with female parasitic wasps, allowing the wasps to inject their eggs directly into the larvae. Seriously, these flies must have been terrified.

A parasitic wasp (Leptopilina heterotoma) probes for fruit fly larvae with her ovipositor.

A parasitic wasp (Leptopilina heterotoma) probes for fruit fly larvae with her ovipositor. (Photo courtesy of Dr. Michael Martin)

Finally, the researchers backcrossed infected females to double-mutant males, and examined the resulting offspring. Sorting through thousands of individual flies, researchers identified recombinant offspring as those that exhibited one mutant trait but not the other.

As predicted by the Red Queen hypothesis, infected females produced significantly more recombinant offspring than non-infected females. The researchers saw this pattern across all types of infection studied, including infection by species that parasitize D. melanogaster in the wild. Furthermore, the effect persisted across host life stages, with females producing more recombinant offspring even when infection occurred during the larval stage of development.

The study also provided some insight on the underlying mechanism for making more recombinant offspring, which – surprisingly – appears not to involve an actual increase in recombination rate. Instead, the culprit looks to be some form of transmission distortion, whereby recombinant gametes are promoted at the expense of non-recombinants.

This study highlights the remarkable ability of individual organisms to rapidly respond to changes in the environment, as well as the central role disease has played in shaping the evolutionary trajectory of animals.

But the reason I’m REALLY excited about these findings is because of their potential to reinvigorate the post-apocalyptic science fiction genre.

Picture this: 50 years after the emergence of an unprecedentedly deadly cross-species pathogen, the majority of the planet’s human population has been wiped out. The only people remaining are the highly recombinant offspring of those infected with (and ultimately killed by) the disease. In a world where survival of the fittest reigns supreme, these exceptionally disease-resistant individuals must attempt to rebuild society as they contend with resource shortages, lawless bands of savages, and the unknown genetic ramifications of the extreme levels of heterozygosity within their population.

It sounds like the beginnings of a pretty solid screenplay to me.

While you’re waiting for my movie to hit theaters, you can read the full text of the Science article here. And check out the video below (courtesy of Dr. Michael Martin), which shows a parasitic wasp female attempting to deposit her eggs in some (probably pretty freaked out) fruit fly larvae.

Speaking of awesome summer epidemics

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I quickly learned while studying disease (and parasites, and coevolution oh my!) that this group of scientist uses strange expressions. For example “Awesome epidemics!”, “Exciting infections!”, “Cool parasitism!”

No, I’m not talking about an increase in the spread of awesome around the world (although now that you mention that…), but rather a tendency to get excited about emerging infectious diseases and pathogen.

This is one of those posts. If disease/parasites/coevolution isn’t your thing, check out this taratula hawk post, this baby bird post, or this sperm whale poop post.

But if you’ve kept reading, then let’s talk about Legionnaires disease. It was first discovered in Philadelphia in 1976, when 221 were sickened and 34 died at an American Legion’s convention (hence the name “Legionnaires disease”).

And this summer, there is another outbreak in the Bronx that has killed 2 so far.

As this is relatively uncommon disease, this outbreak is quite the disease headline! Which you can read all about over at Forbes! The article also includes a list of symptoms for those hypercondriac inclined.

Junk science

Mating Ladybirds

Birds do it, beetles do it … (Flickr: Henry Burrows)

Last spring, the journal Current Biology published a report describing something new under the entomological sun: A genus of tiny cave-dwelling insects, dubbed Neotrogla, in which females, not males, have penises.

Or, rather, the females have a thing that they stick inside the males. Once it’s in there, that thing inflates and latches into the male with tiny barbs, binding the couple together in a copulation lasting two to three days, while the thing collects a packet containing sperm and a whole lot of (potentially) nutritious protein. What to call the females’ thing seems to have puzzled even the scientists who described it. In the text of their paper, they call it a gynosome (literally, a “female body”); but in the title, it’s a “female penis.”

This synonymy went from confusing to controversial the moment it hit the popular science press, which almost uniformly chose to go penis-first. “Female insect uses spiky penis to take charge” read the headline in the prestigious journal Nature. “Meet the female insect with giant PENIS whose steamy sex sessions last 70 HOURS,” said the Daily Mirror, caps-locked emphasis sic. Most of the stories, even the Mirror’s, got around to using the word “gynosome” eventually, and many went into more detail about how the organ in question wasn’t really a penis as we know it. LiveScience noted it was “a complex organ composed of muscles, ducts, membranes and spikes,” before adding that its size, relative to the body of a Neotrogla female, was “the equivalent of a man who is 5 feet 9 inches (1.75 meters) tall having a penis about 9.8 inches (24.9 centimeters) long.”

Continue reading

The Secret Life of Bill Nye

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Bill Nye, formally the Science Guy, now advocate for science education everywhere, is the subject of an upcoming documentary.

And while we look at how the man in the bow tie grew up to be the scientist we all know and love, we need to take a moment to appreciate his mother.

“My mom was a big believer in women doing everything,” Nye said in a new clip from Structure Film’s upcoming documentary. She worked on code breaking during World War II, and was recruited to help decrypt the Enigma code (featured in the recent movie The Imitation Game), at a time when women were even less welcome in STEM careers than we are now.

Want to know more about Bill Nye (I do), then fund the Kickstarter here.

Or read more about him over here.

Note: While I recognize that this post isn’t about biology explicitly, I’m excited that science is mainstream enough to be featured frequently on buzzfeed. I’m also in favor of supporting advocates of science, and as a general biology blog, we want to support communicating science better with the general public. Like my man Bill Nye does.

Additionally, we’re all about promoting women in science on Nothing In Biology. Enjoy.

Don’t take a selfie with a bison

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Apparently this season there has been a series of injuries in Yellowstone National Park.

A woman turned her back on a bison in order to take a photo of herself with the magnificent beast. The bison charged the women, throwing her into the air.

Seriously though, four other tourists have suffered similar fates this year.

As a result, the Yellowstone National Park officials are advising against attempting to take a selfie with a bison.

Just so you know. Read about it over at BBC.

Ancient Sperm

Normally, sperm does not fossilize. They tend to not live very long and have delicate structures.

However, in Antartica scientists have recently uncovered a fossilized worm cocoon. Entrapped in the walls of the cocoon? Sperm.

Importantly it is the oldest known sperm in the world. As in, 10 million years older than then next oldest known fossil of sperm.

Read the paper, published in Biology Letters.

Or read about it in the Guardian here.

sperm

Ecologists, meet the Bronies

“You gotta share, you gotta care” – PinkiePie
This years Ecological Society of America (ESA) meeting is being held at the Baltimore Convention Center and for the first time ever the ESA meeting overlaps with another very important meeting: BronyCon.
For those of us unfamiliar with this cultural phenomenon, Bronies are adults who love my little pony.
The good news is that at BronyCon, cosplay (dressing like my little ponies) is encouraged making it unlikely that there will be much phenotypic overlap. However, one might expect to see some character displacement due to the overlapping conferences, exacerbating phenotypic differences between the two populations of conference attendees. Ecologist should expect to dress a little more “outdoorsy”, while the bronies will obviously move towards a more flamboyant style.
Assuming that Bronies and Ecologists will frequent similar watering holes, conference attendees should expect a greater competition for beverages.While the exacerbated signaling should be enough to differentiate the two conference attendees, we can expect some post hours niche overlap, and increasing competition for resources at bars and coffee shops.
Enjoy!
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