Scientists have assembled the first complete genome of bedbugs, which existed in some form even before humans were around to invent beds.
February 2, 2016 | by Elizabeth Kolbert | The New Yorker
In the great contest that is life, the common bedbug, Cimex lectularius, qualifies as a winner. This is true not just in the Donald Trumpian sense of being extremely difficult to get rid of but in the long-term evolutionary sense of surviving multiple geological epochs. A creature that looked very much like a bedbug was scuttling around during the time of the dinosaurs; a sort of proto-bedbug has been found in amber that’s almost a hundred million years old. It’s not clear what that bug fed on, but it’s believed that long before modern humans—and therefore beds—existed, Cimex lectularius sucked on bats’ blood. When humans took to living in caves, bedbugs descended from the bats and began feeding on people. (There are still bedbugs that prefer bats, and scientists have proposed that the lineage that prefers humans is in the process of becoming a separate species.)
Today, researchers from the American Museum of Natural History and Weill Cornell Medicine announced that they had assembled the complete genome of Cimex lectularius. The same team is working on the cockroach genome; both projects are part of an effort to better understand so-called “living fossils.” A paper on the bedbug genome is appearing today in the journal Nature Communications.
“Bedbugs are one of New York City’s most iconic living fossils,” George Amato, one of the paper’s authors and the director of the museum’s Sackler Institute for Comparative Genomics, noted. The bedbug genome turns out to consist of almost seven hundred million base pairs. This is significantly larger than the fruit-fly genome (a hundred and twenty million base pairs), but not nearly as large as the locust genome (six billion base pairs). In addition to sequencing the bedbug’s genome, the researchers also looked at gene expression over the bug’s life cycle, which spans five instar stages. From this, they concluded that the “first blood meal of the bedbug is the most dynamic period of the bedbug’s transcriptional activity.”
Bedbugs are so-called true bugs. Members of this group also include cicadas, aphids, and leafhoppers, and all share a common arrangement of mouthparts. As anyone who has suffered an infestation knows, bedbugs use their mouthparts, or proboscises, to seek out blood vessels. Then they inject anticoagulants into their victims, to prevent themselves from, in effect, choking. The researchers found that bedbugs possess several classes of genes that code for anticoagulant proteins, including for proteins usually associated with snake venom. This doesn’t mean that bedbugs are any more closely related to snakes than other insects, just that they’ve come up with some of the same strategies.
“What we’re really finding is a structural motif—something about the sequence of amino acids that is probably involved in preventing blood from clotting in the same way a snake venom protein is, but doesn’t share an evolutionary history,” Mark Siddall, another author of the paper and a curator at the Museum of Natural History, explained.
The ancient Greeks were already complaining about bedbugs in the fifth century B.C.; references to bedbugs appear in Aristophanes and then in Aristotle. The bugs seem to have travelled with humans along ancient trade routes; by the seventh century A.D., they were in China, and by the eleventh century in Germany. From Europe, bedbugs migrated to North America and Australia with the colonists.
Bedbugs suffered a population crash in the mid-twentieth century, with the introduction of pesticides like D.D.T. But they have since evolved resistance to many of the chemicals used against them, and their numbers have roared—or, if you prefer, snuck—back up. A recent study by researchers at Virginia Tech and New Mexico State University found that bedbugs have already evolved resistance to neonicotinoids, a class of pesticides that has been in use for only twenty years or so. (The study shows that it takes something like five hundred times the amount of neonicotinoids to kill bedbugs from populations that have been exposed to the chemicals as it takes to kill bugs from populations that have never been exposed.) The researchers who put together the bedbug genome identified several genes that may be involved in pesticide resistance; this information could potentially be used to create more effective bug killers.
“It turns a light on for people to begin in a logical way to explore these areas that we’ve identified,” Amato said.
By combining the information from the genome with information from DNA swabs taken from New York City subway stations, the researchers were also able to map relationships among the city’s bedbug populations. This effort suggests that even bedbugs have a hard time getting across Manhattan.
“We found more north-south connectivity for the bedbugs than we found east-west,” Siddall observed. “And that’s reflecting what we already know to be true.”