February 27, 2013
Parasites have been around for more than 270 million years. Around 25 million years ago, lice joined the blood-sucking party and invaded the hair of ancient primates. When the first members of Homo arrived on the scene around 2.5 million years ago, lice took advantage of the new great ape on the block for better satisfying its digestive needs. As a new genetic analysis published today in PLoS One shows, mining these parasites’ genomes can lend clues for understanding the migration patterns of these early humans.
The human louse, Pediculus humanus, is a single species yet members fall into two distinct camps: head and clothing lice–the invention of clothing likely put this divide into motion. Hundreds of millions of head lice infestations occur each year around the world, most of them plaguing school-aged children. Each year in the United States alone, lice invade the braids and ponytails of an esimtated 6 to 12 million kids between the ages of 3 to 11. Clothing lice, on the other hand, usually infect the homeless or people confined to refugee camps. Clothing lice–also referred to as body lice–are less prevalent but potentially more serious because they can serve as vectors for diseases such as typhus, trench fever and relapsing fever.
Researchers have studied the genetic diversity of head and clothing lice in the past, but scientists from the Florida Museum of Natural History at the University of Florida decided to tap even deeper into the parasites’ genome, identifing new sequences of DNA that could be used as targets for tracking lice evolution through time and space. From these efforts, they found 15 new molecular markers, called microsatellite loci, which could help uncover the genetic structure and breeding history behind different lice populations–and potentially their corresponding humans of choice.
Using those genetic signals, they analyzed the genotypes of 93 human lice taken for 11 different sites around the globe, including North America, Cambodia, Norway, Honduras, the UK and Nepal, among others. They collected lice from homeless shelters, orphanages and lice eradication facilities.
Inbreeding, it turned out, is common in human lice around the world. Lice in New York City shared the most genetic similarities, pointing to the highest levels on inbreeding from the study samples. Clothing lice tended to have more diversity than head lice, perhaps due to an inadvertent bottlenecking of the head lice population due to high levels of insecticides those parasites are regularly exposed to. As a result of repeated run-ins with anti-lice shampoos and sprays, only the heartiest pests would survive, restraining the overall diversity of the population. Insecticide resistance is a common problem in head lice, but less of an issue with clothing lice. The authors identified one possible gene that may be responsible for much of the head louse’s drug resistance, though further studies will be needed to confirm that hunch.
The researchers also analyzed lice diversity to see how it relates to human migration. They found four distinct genetic clusters of lice: in clothing lice from Canada, in head lice from North America and Europe, in head lice from Honduras and in all Asian lice.
Here’s the authors present a map of lice genetic diversity. The colored circles indicate sampling sites, with the different colors referring to the major genetic clusters the researchers identified. The grey flowing arrows indicate proposed migrations of modern humans throughout history, and the colored arrows represent the hypothetical co-migration of humans and lice.
How this geographic structure reflects human migration, they write, will require more sampling. For now, they can only speculate about the implications:
Although preliminary, our study suggests that the Central America-Asian cluster is mirroring the (human host) colonization of the New World if Central American lice were of Native American origin and Asia was the source population for the first people of the Americas as has been suggested. The USA head louse population might be of European decent, explaining its clustering with lice from Europe. Within the New World, the major difference between USA and Honduras may reflect the history of the two major human settlements of the New World: the first peopling of America and the European colonization after Columbus.
Eventually, genetic markers in lice could help us understand interactions between archaic hominids and our modern human ancestors, perhaps answering questions such as whether or not Homo sapiens met with ancient relatives in Asia or Africa besides Homo neanderthalensis. Several kinds of louse haplotypes, or groups of DNA sequences that are transmitted together, exist. The first type originated in Africa, where its genetic signature is strongest. A second type turns up in the New World, Europe and Australia, but not in Africa, suggesting that it may have evolved first in a different Homo species whose base was in Eurasia rather than Africa. If true, then genetic analysis may give us a time period for when humans and other Homo groups for came into contact. And if they interacted close enough to exchange lice, perhaps they even mated, the researchers speculate.
So not only can the genetic structure of parasite populations help us predict how infections spread and where humans migrated, it may give insight into the sex-lives of our most ancient ancestors.
February 18, 2013
The Northeast may be prone to blizzards this time of year, but in Brazil it’s raining spiders. In a video that’s covered the Internet like an immense web, a local photographer captures images of thousands of spiders shimmying up and down silk threads attached to telephone pole wires. The footage gives the distinct impression of a shower–or perhaps light snow–of spiders sprinkling down on the shocked residents below.
Erick Reis, a 20-year-old web designer in Santo Antonio da Platina, a town about 250 miles west of Sao Paulo, captured the striking video that has since accumulated more than 2 million YouTube views over the course of the week. “I was shooting an engagement party for some friends of mine and I saw the spiders when I was leaving, now in the late afternoon,” he explained to TV450000, which posted the video. “I’ve never seen anything like it before.”
According to biologist Marta Fischer of the Pontifical Catholic University of Parana, however, the phenomenon is not so strange. ”This type of spider is known to be quite social,” she said. “They are usually in trees during the day and in the late afternoon and early evening construct sort of giant sheets of webs, in order to trap insects.”
Scientists have described around 40,000 species of spiders around the world, but only a handful of them are social. These 23 species are scattered around the world and sometimes swarm, like ants or bees. Females often outnumber males 10 to 1 in colonies that can exceed 50,000 individuals.
Around Sao Paulo and its neighboring cities, she said, it’s not an unusual site to see a sky speckled by spiders. The species, Anelosimus eximius, can be found from Panama to Argentina and lives in colonies sometimes comprised of thousands of individuals. Each spider is around the size of a pencil eraser. As Examiner reports, the species’ webs can stretch from the ground up to tree canopies or human constructions 65 feet high.
If strong winds come along, the web may detach from its anchors, carrying the spiders and their ruined home to new sites where they appear to “rain down.” Catching rides on the wind–en mass–was likely what happened in Santo Antonio da Platina. While the humans gawked below, the flustered spiders were simply trying to pull themselves together after an unexpected journey from some forest or park.
Before North American readers breathe a sigh of relief that this isn’t happening a bit closer to home, however, it’s worth noting that similar colonies live in Texas. In Lake Tawakoni State Park, just east of Dallas, Guatemalan long-jawed spiders construct enormous webs covering up to 600 foot stretches. The spiders build the huge webs in less than two weeks. Researchers think the spiders achieve such sudden engineering feats thanks to their “remarkable reproductive capabilities and ability to disperse by ballooning,” according to A Field Guide of Scorpions and Spiders of Texas.
So far, Dallas residents haven’t reported massive sheets of webs and their arachnid residents “ballooning” into backyards. But, as witnessed by residents of Santo Antonio da Platina, stranger things have happened.
February 4, 2013
When encountering a two-inch American cockroach, most people quickly skedaddle the other way or raise a foot to stomp the little creeper out of existence. For those curious few who stick around to quietly observe the roach, however, the insect will inevitably fall into a certain diligent, repetitive motion. First, it reaches its spiny little roach feet up towards its head, then grips the base of one of its antennae and finally, as if it were spinning yarn at triple speed, threads the length of its antennae through its furiously working mouthparts.
Insects such as cockroaches, house flies and carpenter ants often engage in such antennae-grooming behavior. Like many animals, scientists know that insects frequently clean themselves, but few researchers have investigated just why bugs bother. Antennae serve not only to feel out the environment but also to sense odors, so researchers have long suspected that grooming keeps the antennae in top shape. But what, specifically, are they scrubbing from their bodies? Do roaches self-clean to remove bacteria or bits of gunk from their last meal?
To figure out just why roaches groom, lead author Katalin Böröczky and colleagues from North Carolina State University along with researchers from the Russian Academy of Sciences observed antennae-cleaning behaviors in a couple dozen adult male American cockroaches, describing their experiment today in Proceedings of the National Academy of Sciences. The researchers used an array of methods to restrain the roaches from self-grooming so that they could compare groomed and ungroomed antennae. In some cases, the scientists used a small plastic clip to tether one antenna at the base of the roaches’ heads. The frustrated insects repeatedly attempted to grab hold of their lassoed antenna but could not get a grip on it in order to clean it. Some roaches also had their mouthparts glued together while others were kept in a box too small to allow for self-grooming.
Here, you can see one of the roaches stymied by the plastic antennae blockers:
Over a period of 24 hours, the tethered antenna began to appear shinier than the other non-tethered one. Examining the shiny antenna with a scanning electron microscope revealed an unidentified substance blocking the roaches’ sensory pores and coating their antennae. The unclean antennae built up three to four times more of the stuff than the clean ones over the day.
To figure out what the unknown build-up was, the researchers took samples of it and analyzed it with gas chromatography, a technique that separates different components of a chemical compound. They found that the natural secretions that the cockroach gives off accounted for most of the substance–mostly fatty molecules that help regulate water loss in insects. Despite the seemingly sterile environment, other external contaminants were stuck on the antennae as well, including stearic acid from surfaces in the roaches’ container and geranyl acetate from the air.
The researchers guessed that this build up might impair the roaches’ ability to sniff out olfactory signals with their antennae. To test this hypothesis, they exposed roaches with groomed and ungroomed antennae to sex pheromones and other odors. Just as they suspected, roaches with clean antennae were more receptive to the odors around them than those with unclean ones. “We conclude that the disruption of grooming interferes with general olfaction,” the authors write in their paper.
Finally, to see if these findings extended to other insects, the researchers repeated their experiment in flies, ants and German cockroaches, all of which exhibited the same build up and loss of antennae function when prevented from self-grooming. They conclude that “our observations with four phylogenetically diverse species indicate that this hitherto unknown role for grooming is common to a wide diversity of insects.”
Just as humans scrub off to remove dead skin cells, sweat and dirt from the day, insects busy themselves to keep clean. While we may share this commonality with earth’s most abundant group of species, however, it may not be quite enough to inspire empathy for the next cockroach that finds its way into a closet or kitchen drawer.
January 24, 2013
Science has shown us that a number of organisms use the stars for navigation: songbirds, harbor seals and, of course, humans. But a new study by a team of Swedish and South African researchers published today in the journal Current Biology indicates that a rather unexpected creature can be added to this list—the lowly dung beetle.
The beetles are known for creating small balls made of animal feces (i.e. dung) and rolling them in straight lines over long distances. They do this because the dung is their main food source—and other beetles often try to steal the dung once it’s been rolled into a ball. The surest way of retaining the valuable dung once it’s been packed into a ball is to move it away from the original dung pile as quickly as possible:
Researchers, though, have long been mystified by the tiny beetles’ ability to roll the dung balls in straight lines at night. “Even on clear, moonless nights, many dung beetles still manage to orientate along straight paths,” said lead author Marie Dacke of Lund University in Sweden. “This led us to suspect that the beetles exploit the starry sky for orientation—a feat that had, to our knowledge, never before been demonstrated in an insect.”
To test the hypothesis, the scientists set up a circular ring with a radius of about 4 feet outside and placed a dung pile at the center. They tested how long it took the beetles to reach the ring from the center—a measure of how straight their paths were—and found that their navigational abilities were relatively similar with either a full moon in the sky or at least a clear view of the stars. When they placed tiny blinders on the beetles’ eyes or subjected them to overcast conditions, though, their paths became much more windy.
Next, they placed a number of beetles in a planetarium and performed a similar test. Their paths were straightest with all the stars turned on, but were almost as true with just the Milky Way—indicating that they are particularly dependent on the Milky Way’s streak of light for navigation.
When the researchers turned on a large number of dim stars—many of which lie in the band of the Milky Way—the beetles’ navigation speed still remained similar. It was only when they left on just 18 of the brightest stars that their pathways became significantly windier.
The authors say that this proves that the beetles don’t rely on one particular star or celestial object for navigation, but rather take in the totality of the Milky Way—which appears as a startlingly bright band of light in many rural areas—to orient themselves on the ground.
December 19, 2012
The year is 2051. Given the realities of climate change and regulations on carbon emissions, beef and pork–protiens with high carbon footprints–have become too expensive for all but the most special of occasions. Luckily, scientists have developed an environmentally-friendly meat solution. Sitting down for dinner, you grab your fork and look down at a delicious plate of….mealworms.
That, anyway, is one possibility for sustainable meat examined by Dennis Oonincx and Imke de Boer, a pair of scientists from the University of Wageningen in the Netherlands, in a study published today in the online journal PLOS ONE.
In their analysis, cultivating beetle larvae (also known as mealworms) for food allowed the production of much more sustainable protein, using less land and less energy per unit of protein than conventional meats, such as pork or beef. In a 2010 study, they found that five different insect species were also much more climate-friendly than conventional meats—a pound of mealworm protein, in particular, had a greenhouse gas footprint 1% as large as a pound of beef.
“Since the population of our planet keeps growing, and the amount of land on this earth is limited, a more efficient, and more sustainable system of food production is needed,” Oonincx said in a statement. “Now, for the first time it has been shown that mealworms, and possibly other edible insects, can aid in achieving such a system.”
This prospect might seem absurd—and, for some, revolting—but the problem of greenhouse gas emissions resulting from meat production is quite serious. The UN estimates that livestock production accounts for roughly 18% of all emissions worldwide, caused by everything from the fuel burned to grow and truck animal feed to the methane emitted by ruminants such as cows as they digest grass. Of most concern, since world populations are increasing and growing more wealthy, is that the demand for animal protein is expected to grow by 70-80% by 2050.
Insects like mealworms, the researchers suggest, can help to solve this problem. Since they aren’t warm-blooded (like mammals) they expend far less energy per pound as part of their metabolism, so they needn’t eat as much to survive. As a result, less energy goes into cultivating them as a food source, and less carbon dioxide gets emitted into the atmosphere.
The researchers came to this conclusion by conducting an environmental impact assessment for a commercial mealworm producer in the Netherlands (mealworms are often cultivated as a food for reptile and amphibian pets). They analyzed every input used in the process of rearing the worms, including the energy used to heat the incubators, the grain used as feed and the cardboard used for rearing cartons. Even including all these inputs, the worms were much more climate-friendly than conventional protein sources.
Sure, you might be pretty reluctant to sit down to a bowl of mealworm macaroni, but in a number of places around the world—especially in Asia—they’re considered a perfectly normal food. Even some people here in the U.S. agree: A quick search reveals mealworm recipes you can cook up at home, like mealworm french fries and stir-fried mealworms with egg, while Mosto, a trendy restaurant in San Francisco, serves crispy mealworms over ice cream.
Better yet, mealworms are more healthy than conventional meats, too. According to PBS, a pound of mealworms has more protein and half as much fat as a pound of pork.
Still, there is one inescapable obstacle to widespread mealworm consumption: the “yuck” factor. For those of us who don’t typically eat insects, a forkful of mealworms triggers a profound feeling of disgust. Even this blogger—fully convinced of the wisdom of eating insects—can acknowledge from personal experience (an encounter with a bag of fried mealworms in Thailand) that knowing the worms are okay to eat and actually eating them are entirely separate matters.