Cockroaches diversified earlier than thought

Around the globe there are nine recognised families of cockroaches – and new research has found that they last shared a common ancestor about 235 million years ago.

The finding, by a team led by Thomas Bourguignon of the School of Life and Environmental Sciences at the University of Sydney in Australia, is significant because the estimate predates the break-up of the super-continent Pangaea.

This modifies the idea that tectonic plate drift – the result of the continent fracturing – was the major factor in driving the evolution of the insects into separate groups. The date of the last common ancestor also turns out to have been a hefty 95 million years earlier than the appearance of fossils that can be reliably assigned to the nine current families.

To make their finding, Bourguignon and colleagues analysed the complete mitochondrial genomes of 119 living cockroach species, looking for common gene and protein sequences which can be used as a base for estimating when the species diverged from each other. By tracing the common elements backwards – in a process known as phylogenetic analysis – they were able to zero in on the time when all the genomes shared a single source.

Moving forwards, the scientists reconstructed geographical ranges for ancestral cockroaches and found “tentative support” for tectonic plate movement as a later mechanism that caused geographic separation and drove the divergence between families – a phenomenon known as vicariance.

They also found evidence that variations between species found in Australia, the Indo-Malaya, African and Madagascan regions had been influenced by insects dispersing across oceans.

The research is published in the journal Molecular Biology and Evolution.