Me, Myself and I: Crows Choose Partner that Look like Them

No they aren't conceited. A new study by Uppsala University found that crows like to select mates that look like themselves, but that this behavior may be rooted in their genetic makeup, revealing a likely common evolutionary path that allows for separating populations into novel species.

This large-scale genomic study, published Thursday in the journal in Science, takes another look at an idea put forth by scientist Charles Darwin, who said that all species are subject to evolutionary change. We now know that the driving engine behind biodiversity is the genome, yet how new species emerge from slight genetic changes is a question still unanswered.

For instance, crows are all black or grey coated, and they exhibit a strong tendency to select partners that look like themselves.

Using crows and ravens of the genus Corvus, researchers aimed to find out the genetic foundations of speciation. Specifically, they looked at all black carrion crows and grey coated hooded crows that still hybridize along a hybrid zone stretching across Europe and Asia.

Both species of birds, despite living in such narrow hybrid zones, have somehow managed to still keep separate. Previous small scale genetic analysis showed hardly any genetic differentiation between carrion and hooded crow across the entire species range compared to what is typically seen between populations of the same taxon.

Screens of the more than one billion base pairs in their genomes revealed very little difference between the two birds. Only 82 base pairs were diagnostically different, and 81 of them were involved in coding for coloration and visual perception.

"This finding suggests the exciting possibility that a mate-choice relevant trait, like coloration, might be genetically coupled to its perception which could be common one evolutionary path allowing for separating populations into novel species," lead author Jochen Wolf said in a statement. "Such a mechanism could be common for many other species with visually oriented mate choice."