Amazing stuff!
"The German cockroach, the world’s most abundant kind, lives only among humans—and humans may be to blame for its spread. A genetic study published yesterday finds that medieval warfare and colonial trade helped it expand to nearly every corner of the globe.
The ubiquitous pest was first described in Europe in 1776, but DNA shows it had already made epic travels. A family tree based on 281 specimens from 17 countries indicates that its expansion began about 2100 years ago, after the German cockroach diverged from an Asian species, probably in India or Myanmar. It moved westward to the Middle East about 1200 years ago with the expansion of trade and warfare under two Islamic caliphates, the Umayyad and the Abbasid. The insects may have crossed the deserts by hitchhiking in bread baskets, the researchers say.
Next, about 390 years ago, the species expanded eastward to Southeast Asia, riding colonial trade routes. Within about a century, the roaches had arrived in Europe. More recently, steamships and improved housing—heating and plumbing create the warm, moist conditions cockroaches love—enabled the itinerant insects to spread around the globe. “The researchers show that adaptation to the human lifestyle was key for the spread, which I think is really original,” says conservation biologist Cleo Bertelsmeier, who was not involved in the work."
From the abstract:
"The origin of the German cockroach, Blattella germanica, is enigmatic, in part because it is ubiquitous worldwide in human-built structures but absent from any natural habitats. The first historical records of this species are from ca. 250 years ago (ya) from central Europe (hence its name). However, recent research suggests that the center of diversity of the genus is Asian, where its closest relatives are found. To solve this paradox, we sampled genome-wide markers of 281 cockroaches from 17 countries across six continents. We confirm that B. germanica evolved from the Asian cockroach Blattella asahinai approximately 2,100 ya, probably by adapting to human settlements in India or Myanmar. Our genomic analyses reconstructed two primary global spread routes, one older, westward route to the Middle East coinciding with various Islamic dynasties (~1,200 ya), and another younger eastward route coinciding with the European colonial period (~390 ya). While Europe was not central to the early domestication and spread of the German cockroach, European advances in long-distance transportation and temperature-controlled housing were likely important for the more recent global spread, increasing chances of successful dispersal to and establishment in new regions. The global genetic structure of German cockroaches further supports our model, as it generally aligns with geopolitical boundaries, suggesting regional bridgehead populations established following the advent of international commerce."
Solving the 250-year-old mystery of the origin and global spread of the German cockroach, Blattella germanica (open access)
Fig. 1 Population genetic structure and global spread routes of the German cockroach, Blattella germanica.
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