2 Raven Species Merge Through Evolutionary Process 'Speciation Reversal'

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Two different lineages of common ravens that have separated and evolved from each other millions of years ago merged again as one. This evolutionary process is known as speciation reversal or lineage fusion.  ( Pixabay )

Speciation is a concept in evolutionary process wherein new and distinct species are formed. A new research discovered the reversal of speciation in ravens.

The study, which is the product of an almost 20-year research and investigation, now has evidences of speciation reversal, or the process wherein species that collapsed into different hybrids many years ago merge again to a single lineage or lineage fusion.

This was proved through an extensive study of common ravens (corvus corax) from two different lineages, the California, and Holarctic ravens.

Lineage Fusion

California ravens are concentrated in the southwestern United States while Holarctic ravens can be found everywhere including Alaska, Norway, and Russia.

These two species of ravens have spent between 1 to 2 million years evolving separately. The study suggests that these ravens are now in the process of lineage fusion.   

"The bottom line is [speciation reversal] is a natural evolutionary process, and it's probably happened in hundreds, or almost certainly thousands, of lineages all over the planet," says Kevin Omland, professor of biological sciences at University of Maryland, Baltimore County and coauthor of the new study.

Raven Families                                      

For the study, the researchers combed through the DNA of 441 common ravens.

Holarctic ravens are the most widespread of all the raven species.

The common California raven has a large, heavy bill, and glossy pointed neck feathers. About 1.5 million years ago, this species separated from the rest of the ravens. The separation allowed the California ravens to evolve into a different species.

Another species related to the California raven is the Chihuahuan raven (Corvus cryptoleucus). The Chihuahuan ravens do not interbreed with the other two species.

The ancestors of the California and Chihuahuan ravens have split from the Holarctic ravens in the Pleistocene era. Several hundred thousand years ago, the common ravens contacted the California raven species again. This led to their speciation reversal through merging and hybridization.

Pure California ravens do not exist anymore. They merged with the Holarctic ravens and other hybrid common ravens from the two original lineages.

"This is definitely an ancient speciation reversal event," says Anna Kearns, study coauthor and a research fellow at the Smithsonian Conservation Biology Institute.

Method Of Genomic Investigation

The researchers studied the individual genomes of the raven species at a special ancient DNA laboratory at the Smithsonian's Center for Conservation Genomics.

The analysis of the mitochondrial DNA of the raven species revealed that the hybrids and the Holarctics have a difference of only 4 percent.

To be considered as two distinct species, the difference in DNA should be twice as with other known bird species.

The study is published in the journal Nature Communications.

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