Bacterial Thunderdome: Decoding virulence, spiteful interactions, and diversity

What happens when two parasites infect the same host individual? Is the outcome similar to the Thunderdome: two parasites enter, one parasite leaves? Host-parasite interactions are rarely so simple. While a reductionist approach to understanding the interaction of a parasite or pathogen with its host may decompose the system to a single infection, nature is full of much more complex puzzles. Within the host, the battle itself raging between parasites (within-host competition) may have cascading effects on the host.
Bashey et al 2012 wordle
A recent paper on virulence caught my eye (Bashey et al., 2012) which provides an update to a very interesting result from the group a few years ago. The system includes bacterial parasites, along with parasitic nematodes, that infect insect larvae and eat/digest them from the inside out. Vigneux et al. (2008) found that when multiple parasite isolates are mixed in a host, the host mortality decreased. However, this only occurred when the isolates were not related. In the experiment, the researchers created low relatedness by mixing populations with migration. I reviewed the 2008 paper over at the Coevolvers blog, my personal science blog. The hypothesis was that chemical warfare among the parasites decreased the parasite load and reduced the negative effects on the host, virulence.
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Friday coffee break

Experimental coffee

NiB does not endorse drinking coffee at your lab bench. No, sir.

Every Friday at Nothing in Biology Makes Sense! our contributors pass around links to new scientific results, or science-y news, or videos of adorable wildlife, that they’re most likely to bring up while waiting in line for a latte.

From Sarah: Herpetologists have discovered teeny tiny chameleons on Madagascar. Unfortunately, they’re as endangered as they are adorable.

Scientists believe the small ranges of the species make them especially sensitive to habitat disturbance.

B[rookesia] tristis, named after the French word “triste” meaning sad, was found in an isolated patch of forest close to an expanding city.

From Jon: A new implantable microchip could be used for drug delivery.

The chip is one-fiftieth of an inch thick and measures half an inch long by a fifth of an inch wide. It contains 10 cube-shaped reservoirs, 40 one-thousandths of an inch on each side. Each holds 600 nanoliters of a highly concentrated solution of the drug.

The side of the reservoirs that touches human tissue is covered with a metallic membrane, a composite of titanium and platinum, wired to internal electronics that provide a path for an electrical current. To deliver the drug, the membrane is melted.

And, from Jeremy: A new technology for collecting DNA sequence seo company data promises to be a major step forward. But the error rate may be a problem.

According to Nanopore, the ‘indel’ error rate is about four percent. That is, every four out of one hundred bases, a base is either erroneously added or deleted due to sequencing error. …

… the problem comes when we try to annotate the genome–that is, figure out what the genes are contained in the sequence. In my experience, technologies that have a lot of ‘indels’ in the raw sequence end up with lots of ‘broken genes’ because enough of those indels wind up in the final, assembled genome (for the cognoscenti, a 1-in-10,000 final indel rate will bust up lots of genes).

In flour beetles, coevolution mixes things up

A red flour beetle. (Image via Wikimedia Commons.)

When evolutionary biologists think about sex, we often think of parasites, too. That’s not because we’re paranoid about sexually transmitted infections—though I’d like to think that biologists are more rigorous users of safer sex practices than the general population. It’s because coevolution with parasites is thought to be a major evolutionary reason for sexual reproduction.

ResearchBlogging.orgThis is the Red Queen hypothesis, named for the character in Lewis Carroll’s Through the Looking Glass who declares that “it takes all the running you can do to keep in the same place.” Parasite populations are constantly evolving new ways to infest and infect their hosts, the thinking goes. This means that a host individual who mixes her genes with another member of her species is more likely to give birth to offspring that carry new combinations of anti-parasite genes.

But although sex is the, er, sexiest prediction of the Red Queen, it’s not the whole story. What matters to the Red Queen is mixing up genetic material—and there’s more to that than the act of making the beast with two genomes. For instance, in the course of meiosis, the process by which sex cells are formed, chromosomes carrying different alleles for the same genes can “cross over,” breaking up and re-assembling new combinations of those genes. Recombination like this can re-mix the genes of species that reproduce mostly without sex; and the Red Queen implies that coevolution should favor higher rates of recombination even in sexual species.

That’s the case for the red flour beetle, the subject of a study just released online by the open-access journal BMC Evolutionary Biology. In an coevolutionary experiment that pits this worldwide household pest against deadly parasites, the authors show that parasites prompt higher rates of recombination in the beetles, just as the Red Queen predicts.

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Friday coffee break

Coffee flasks

Siphoned coffee.

Every Friday at Nothing in Biology Makes Sense! our contributors pass around links to new scientific results, or science-y news, or videos of adorable wildlife, that they’re most likely to bring up while waiting in line for a latte.

From Devin: A new service, Peerage of Science, which conducts peer review of scientific articles independently of any single journal, is evaluated in the pages of Trends in Ecology and Evolution; see also the response by Peerage of Science.

First, PoS aims to enhance the quality of reviewing by encouraging non-anonymous review, introducing ‘peer review of peer review’, providing the possibility for reviewers to publish their review as a ‘Peerage Essay’ (PE) and to build a ‘referee factor’. Previous attempts at non-anonymous review have discovered, however, that most reviewers prefer anonymity. Peer review of peer review and the implementation of a referee factor are certainly good ideas, but reviewers who want to remain anonymous would waste their time writing a PE. Additionally, it will not always be possible to have an original insight and bring new perspectives to every evaluated paper, and the PE could become outdated after manuscript revision. A solution could be to let the comments to authors be assessed by the other reviewers and make the writing of a PE optional. [In-text citations removed.]

(Jeremy also notes that PoS is either an unfortunate, or a brilliant, abbreviation for a peer review system.)

From Sarah: For the week of Valentine’s Day, Paleontology writer Bryan Switek considers what we know about the mating habits of dinosaurs.

Rather than simply leaning straight against the top of a female like an elephant or rhinoceros does, a male sauropod would probably have to rear up at a relatively oblique angle, and the female would have to assist by moving her tail (which is also a way in which female dinosaurs could have exerted mate choice and confounded any hot-under-the-collar males they would rather not mate with).

From Jon: New research finds that interval training—exercise in a series of brief bursts—can improve fitness faster than more time spent in sustained exertion.

Several years ago, the McMasters scientists did test a punishing workout, known as high-intensity interval training, or HIIT, that involved 30 seconds of all-out effort at 100 percent of a person’s maximum heart rate. After six weeks, these lacerating HIIT sessions produced similar physiological changes in the leg muscles of young men as multiple, hour-long sessions per week of steady cycling, even though the HIIT workouts involved about 90 percent less exercise time. [Links sic.]

From Jeremy: Documents leaked from a conservative think-tank with ties to companies like GM and Microsoft reveal plans to excise climate change from basic science education.

One thing I want to point out right away which is very illuminating, if highly disturbing, about what Heartland allegedly wants to do: they are considering developing a curriculum for teachers to use in the classroom to sow confusion about climate change. I know, it sounds like I’m making that up, but I’m not. In this document they say:

[Dr. Wojick's] effort will focus on providing curriculum that shows that the topic of climate change is controversial and uncertain – two key points that are effective at dissuading teachers from teaching science.

[Links and formatting sic.]

How to celebrate Valentine’s Day: A note on the Red Queen and maintaining sexual reproduction

This year's Valentine's card of choice

HAPPY VALENTINE’S DAY! As a perpetually single girl this is my favorite holiday of the year. The first and second half of those statements may appear conflicted. However, every year on Valentine’s Day, I send out glorious amounts of Valentine’s to all my single friends (See below for this years!), eat chocolate and drink red wine while ordering myself sexy lingerie on the internet. Yeah, it’s a pretty awesome holiday. This year, one of my favorite evolutionary biologists has upped the excitement by publishing a paper on what conditions favor sex! Perfect for Valentine’s Day!

Why organisms reproduce sexually is one of the great mysteries in evolutionary biology (I’d like to note that here I’m talking about sex in terms of reproduction. It isn’t a mystery to me why organisms copulate, the differences being if that sex comes with offspring while copulation is just good old fashioned fun). There are a number of theoretical reasons that they shouldn’t! One of the strongest arguments was first laid out by John Maynard Smith (1978) who noted that an asexual female can produce twice as many offspring per individual than a sexual female, who wastes half of her effort producing males. This almost immediately results in sexuals being driven to extinction and is termed “the two-fold cost of males.”

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Happy Darwin Day!

Charles Darwin

Cross-posted from Denim and Tweed.

Charles Darwin, who first proposed that natural selection could be responsible for “descent with modification,” the observation (which predates Darwin) that living species change over time and give rise to new species, was born on this day in 1809.

By all accounts, Darwin was a geek’s geek—uncomfortable in high-pressure social situations and devoted to the fiddly details of his scientific work. But he also seems to have been a quietly friendly chap, keeping up a tremendous volume of correspondence with other scientists all over the world, and, most charmingly, bringing his children into the fun of puzzle-solving that lies at the heart of science.

I don’t know of better proof of this than this account of Darwin’s familial experimentation, produced for NPR by Robert Krulwich with writer David Quamman, a couple years back around the Darwin Bicentary. (Thanks to Madhusudan Katti for reminding me about it!)

http://www.npr.org/v2/?i=6105541&m=6105662&t=audio

Friday coffee break

Musical coffee

Every Friday at Nothing in Biology Makes Sense! our contributors pass around links to new scientific results, or science-y news, or videos of adorable wildlife, that they’re most likely to bring up while waiting in line for a latte.

From Noah: Paleontologists reconstruct the song of a fossilized Jurassic-era katydid.

Examining the insect’s seven centimeter long fossil wings under microscope, researchers were able to see how the prehistoric male katydid employed stridulation, i.e. rubbing body parts together, to produce a song to attract a female.

From Jon: A tranquilizer that is commonly abused as a club drug shows great promise for treating depression.

And the patient, they say, you know, yeah, it helped with my pain, but, you know, my depression seemed better. And so this was sort of a curiosity for a long time until a few years ago, when some folks at the National Institutes of Health decided that they really wanted to check this out.

From Sarah: The New York Times on the natural history of venomous mammals.

Every so often, however, a mammalian lineage discovers the wonders of chemistry, of nature’s burbling beakers and tubes. And somewhere in the distance a mad cackle sounds.

Skunks and zorilles mimic the sulfurous, anoxic stink of a swamp. The male duck-billed platypus infuses its heel spurs with a cobralike poison. The hedgehog declares: Don’t quite get the point of my spines? Allow me to sharpen their sting with a daub of venom I just chewed off the back of a Bufo toad.

From Jeremy: Antibiotic-resistant strains are now so widespread that we may soon see the day when gonorrhea is untreatable.

Gonorrhea is one of the most common sexually transmitted diseases in the world—with about 600,000 cases diagnosed in the U.S. each year. A few years ago, investigators started seeing cases of infection that did not easily respond to treatment with a group of drugs called cephalosporins, which are currently the last line of defense against this particular infection. Now, the number of drug-resistant cases has grown so much in the U.S. and elsewhere that gonorrheal infection may soon become untreatable, according to doctors writing in the February 9 issue of the New England Journal of Medicine. [Link sic.]

And, from Devin: Adrien Treuille discusses the power of online, collaborative puzzle solving for Google’s “Solve for X.”

Why grow thorns if they don’t work?

This post is a guest contribution by Colin Beale, a research fellow at the University of York who studies ecology in Tanzania. Colin writes about the living community of the savannah, from butterflies to wildebeests, with co-blogger Ethan Kinsey at Safari Ecology. If you have an idea for a post, and you’d like to contribute to Nothing in Biology Makes Sense, e-mail Jeremy to inquire.

Giraffes lick leaves from between the thorns.

Spinescent. Now there’s a word! It simply means having spines and one of the first things many visitors to the African savannah notice is that everything is covered in thorns. Or, in other words, Africa is spinescent. It’s not a wise idea to brush past a bush when you’re walking, and you certainly want to keep arms and legs inside a car through narrow tracks. These are thorns that puncture heavy-duty car tyres, let alone delicate skin. But why is the savanna so much thornier than many of the places visitors come from? Or even than other biomes within Africa, such as the forests?

At one level the answer is obvious—there are an awful lot of animals that like to eat bushes and trees in the savanna. Any tree that wants to avoid this would probably be well advised to grow thorns or have some other type of defence mechanism to protect itself. But then again, perhaps the answer isn’t so obvious: all those animals that like to eat bushes seem to be eating the bushes perfectly happily despite the thorns. So why bother having thorns in the first place? There’s certainly a serious cost to having thorns: plants that don’t need to grow them have been shown in experiments to produce more fruits. So if animals eat the plants with thorns anyway, why pay this cost?

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A post about inbreeding depression in which I make no reference to the movie “Deliverance.”

Bighorn sheep (Ovis canadensis) at Glacier National Park in Montana. Photo by Noah Reid.

As humanity spreads out over the globe, finding ever more clever ways to domesticate wild landscapes and harness natural processes to its will, many species of wildlife find their natural distributions becoming fragmented.  Iconic North American species such as grizzly bears, red-cockaded woodpeckers, and the American burying beetle today inhabit only small fractions of the ranges they occupied only 100 years ago. A result of this fragmentation is that many individuals exist in small, isolated populations.  In these populations, a curious phenomenon often emerges, one that can only be understood in light of some basic evolutionary theory.  That phenomenon is known as inbreeding depression, and it refers to the decline in average fitness of individuals in a shrinking population.

Inbreeding depression is essentially a result of individuals in small, isolated populations being more likely to mate with close relatives.  It’s well known that mating with close relatives produces less fit offspring, and the aggregate effect in natural populations is seen as low average fitness and an ensuing low population growth rate.  This can be a serious problem in populations subject to conservation efforts because even after protective measures have been taken (removing threats, restoring habitat) recovery can be hindered by inbreeding depression.  Inbreeding depression is slightly more complicated than this, however, because it is not consistently seen in all small populations.  In some island populations with very small population sizes (such as the Chatham Robin, Petroica traversi) inbreeding depression has not been observed (Jamieson et al. 2006).

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Friday coffee break

Every Friday at Nothing in Biology Makes Sense! our contributors pass around links to new scientific results, or science-y news, or videos of adorable wildlife, that they’re most likely to bring up while waiting in line for a latte.

From Jon: Drug-resistant bacteria have been found on pork products raised without antibiotics. (But note that this doesn’t necessarily mean antibiotic-free farming is futile.)

The researchers found that 64.8% of the samples were positive for staph bacteria and 6.6% were positive for MRSA. Rates of contamination were similar for conventionally raised pigs (19 of 300 samples) and those labeled antibiotic-free (seven of 95 samples). Results of genetic typing identified several well-known strains, including the so-called livestock-associated MRSA (ST398) as well as common human strains; all were found in conventional and antibiotic-free meat. (The label “antibiotic-free” is not regulated, and the products were not “certified organic.”) [Hyperlink sic.]

From Sarah: New paleontological finds suggest dogs were first domesticated as long as 33,000 years ago. (See also The Onion‘s related person-on-the-street interviews.)

Researchers at UA and universities in England and the Netherlands used radiocarbon dating to determine that the skull of a Siberian dog was about 33,000 years old. Slightly older dog remains were identified in Belgium a few years ago by a separate research team.

Devin suggests Daniel Simons’s guide to scientific writing and revising.

Every section of your introduction should build directly on the previous ones, maintaining the narrative flow established by your opening. If your paper is organized as an unsolved mystery, each paragraph should add clues. If your paper is organized as a fiery controversy, each paragraph should add fuel. If a paragraph doesn’t contribute, cut it.

And finally, from Jeremy: some clever dissection work has revealed that, for orb-web spiders, mating continues even after the male’s intromittant organ breaks off inside his mate.

“It is quite remarkable,” says Jutta Schneider, who studies sexual interactions in spiders at the University of Hamburg in Germany. “It supports our notion that male spiders of some species are under selection to prolong copulation against the actions of the female.”