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Two species of ravens nevermore? New research finds evidence of 'speciation reversal'

For over a century, speciation—where one species splits into two—has been a central focus of evolutionary research. But a new study almost 20 years in the making suggests "speciation reversal"—where two distinct lineages hybridize and eventually merge into one—can also be extremely important. The paper, appearing March 2 in Nature Communications, provides some of the strongest evidence yet of the phenomenon, in two lineages of Common Ravens.
"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," said Kevin Omland, professor of biological sciences at University of Maryland, Baltimore County (UMBC) and co-author on the new study. "One of our biggest goals is to just have people aware of this process, so when they see interesting patterns in their data, they won't say, 'That must be a mistake,' or, 'That's too complicated to be correct.'"

Read more at: https://phys.org/news/2018-03-species-ravens-nevermore-evidence-speciation.html#jCp



the paper:


Genomic evidence of speciation reversal in ravens:


Many species, including humans, have emerged via complex reticulate processes involving hybridisation. Under certain circumstances, hybridisation can cause distinct lineages to collapse into a single lineage with an admixed mosaic genome. Most known cases of such ‘speciation reversal’ or ‘lineage fusion’ involve recently diverged lineages and anthropogenic perturbation. Here, we show that in western North America, Common Ravens (Corvus corax) have admixed mosaic genomes formed by the fusion of non-sister lineages (‘California’ and ‘Holarctic’) that diverged ~1.5 million years ago. Phylogenomic analyses and concordant patterns of geographic structuring in mtDNA, genome-wide SNPs and nuclear introns demonstrate long-term admixture and random interbreeding between the non-sister lineages. In contrast, our genomic data support reproductive isolation between Common Ravens and Chihuahuan Ravens (C. cryptoleucus) despite extensive geographic overlap and a sister relationship between Chihuahuan Ravens and the California lineage. These data suggest that the Common Raven genome was formed by secondary lineage fusion and most likely represents a case of ancient speciation reversal that occurred without anthropogenic causes.

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Interestring. This would provide support, would it not, for those who favour a multi-regional origin for homo sapiens over the more popular Out of Africa?

On the more general point, this is not surprising and is implicit in many studies, but it is encouraging to see it spelled out and supported in a specific (pun intended) situation.

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Not an expert on evolution or even a biologist but I think I have assumed this (speciation reversal as a potential and likely process) as obvious once I realized that the definition of species is less rigid than I was originally taught back in grade school.

I guess the devil is in the details.

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