The German cockroach (in photo) was found to be a descendant of the Asian cockroach, Blattella asahinai, that lived in human settlements in South Asia around 2,100 years ago.

Cockroaches are the bane of homeowners worldwide. Throughout history, these die-hard critters have evolved and spread at an increasing rate, posing profound implications for human well-being and economic prosperity. The German cockroach, Blattella germanica, is one of the most common and resilient household pests infesting human settlements globally. Infestation rates have increased due to German cockroaches’ rapid evolution of insecticide resistance.

Despite what its name may suggest, recent research on the German cockroach reveal possible links of its lineage back to Asian origins, where its closest relatives are found. To solve this mystery, a research team led by Associate Professor Frank Rheindt from the Department of Biological Sciences under the NUS Faculty of Science studied the population genomics of this species of cockroach to reveal its ancestral roots, which is key to understanding its rapid spread and adaptation abilities, paving the way for new approaches to integrated pest management.

The findings from this study were published in PNAS on 20 May 2024.

The photo shows two German Cockroach specimens collected about a century ago. The research team analysed German cockroach specimens from 17 countries across six continents to track down its ancestral journey across the world. (Photo by Dr Tang Qian. Specimens provided by Harvard Museum of Comparative Zoology.)

Mapping the travels of the German cockroach

Historical records indicate a European origin for the German cockroach’s global spread that started 250 years ago. However, these records are geographically biased and clouded by a lack of entomological knowledge of non-European regions before the 20th century.

To help fill this knowledge gap, the research team collected 281 cockroach samples from 17 countries across six continents to produce the world’s first comprehensive map of the population genetic structure for the German cockroach. The researchers employed genomic techniques to develop a dataset containing the genetic information of the cockroach samples, allowing them to trace their journey and genetic heritage across the world.

Assoc Prof Rheindt said, “With the use of genomic tools, we are able to elucidate the origins and spread of species in ways that we had never dreamt before, affording us unexpected opportunities.”

From their analysis, the research team confirmed that the German cockroach is a descendant of the Asian cockroach, Blattella asahinai, probably living in human settlements in South Asia around 2,100 years ago. The researchers also demonstrated the two routes – west and east of the origin of India or Myanmar – which the German cockroach took during its journey around the world.

Their travels westward took place around 1,200 years ago to the Middle East as German cockroaches were known to hitchhike in the bread baskets of soldiers. More recently, around 390 years ago, the German cockroach ventured east, facilitated by European colonial activities between South and Southeast Asia. The researchers estimated that its entry into Europe was not until as recent as the 18th century, matching the historical records in the 1760s.

The team also outlined the routes taken by the German cockroach as it spread to the rest of the world between the late 19th and early 20th century, which coincides with innovations, such as the steam engine and indoor plumbing, allowing the cockroaches to travel further across the world and colonised areas that were not previously accessible.

Dr Tang Qian, who is the first author of the study, said, “It is amazing that the German cockroach evolved from a 200-million-year-old genus and, within such a short time, acquired novel traits to adapt to the anthropogenic environment.”

From their findings, the researchers suggest that future studies on German cockroaches should be reorientated to focus on Asia, where they have found its highest level of genetic diversity.

“On top of confirming its Asian origin, this study also provides an analytical framework, using cutting-edge population genomic approaches, for future studies to explore the mechanisms of historical biological invasions when records are sparse and regionally biased,” said Assoc Prof Rheindt.

Next steps

In the next phase of their work, the researchers plan to conduct further studies on the German cockroach to explore the evolution of its functional and adaptive traits, such as insecticide resistance, cooperative foraging, and complex social interactions. Through these studies, the team hopes to deepen the understanding of the evolution of these traits, which may help develop new strategies for effective pest control.



News from: https://news.nus.edu.sg/tracing-the-odyssey-of-the-fittest-cockroach/