Crows select mates that look alike

Genes drive crows to choose partners that look like themselves, a new study has found.
A large-scale genomic study found that crows like to select mates that look alike and this behaviour might be rooted in their genetic make-up.
The researchers led by Uppsala University identified an avian system - crows and ravens of the genus Corvus - that they used as an evolutionary model to decipher the genetic underpinnings of speciation - the evolutionary process by which new biological species arise.
The study focused on the young end of the evolutionary spectrum investigating the genetic architecture of divergence between all black carrion crows and grey coated hooded crows that still hybridise along a hybrid zone stretching across Europe and Asia.

Hybrid zones are natural evolutionary experiments where early processes of speciation can be studied.
Researchers set out to find the decisive differences that eventually keep carrion and hooded crows apart using a plethora of approaches.

They generated a genome backbone, performed population genetic analyses of whole genome data of many individuals, raised young crows to measure gene expression under controlled conditions and conducted functional histological characterisation of growing feather follicles to have a closer look at melanocytes, the cells where colour is made.
Consistent with the hypothesis of colour-mediated isolation, they found that gene expression differed almost exclusively in growing feather follicles at the stage where colour is deposited into the feathers.

Genes involved in colouration were constitutively expressed higher in black crow than in their grey counterparts.
Screens of the more than 1 billion base pairs in the genome showed very little difference between the two. Only 82 base pairs were diagnostically different and 81 of them were concentrated in one genomic region coding for genes involved in colouration and visual perception.
"This finding suggests the exciting possibility that a mate-choice relevant trait, like colouration, might be genetically coupled to its perception which could be common one evolutionary path allowing for separating populations into novel species," researchers said.
"Such a mechanism could be common for many other species with visually oriented mate choice," they said.