Evolution of female-limited colour polymorphism through sex-specific genetic architecture in cuckoos

Theevolution of sex-specific traits has long been the subject of interest amongevolutionary biologists. In birds, female-limited plumage color may result fromconflicting selective pressures, in males and females, leading to intra-locussexual conflict. The common cuckoo (Cuculus canorus) is a prime exampleof female-limited color polymorphism, where adult females exhibit either rufousor grey plumage, while males are monochromatic grey. This species is well-knownfor its interspecific brood parasitism and morph prevalence seems to be under frequency-dependentselection by host recognition. Alternative plumage coloration may alsofunction intraspecifically to reduce sexual harassment and intrasexualaggression caused by competition for critical resources. However, the geneticbasis of this pivotal trait and the evolutionary mechanisms maintaining itremain obscured. Here, we identify the genomic region underlying the evolutionof the rufous plumage coloration, in female cuckoos, and investigate thepotential role of balancing selection in maintaining female-limited colorpolymorphism. We show that intra-locus sexual conflict may be resolved byensuring sex-biased inheritance and suggest that balancing selection canincrease a species’ adaptive potential. Taken together, the findings of thisstudy shed light on the evolution of sex-specific polymorphisms and itspotential for new avenues in the study of bird coloration.

Cristiana Marques is a BIODIV PhD student in EVOLGEN research group at BIOPOLIS/CIBIO-InBIO. Her main research interest sets on understanding the mechanisms leading to and shaping phenotypic diversity, with especial interest on behavioral phenotypes and coloration. During her MSc, she investigated the genetic mechanisms underlying plumage color variation in Gouldian finches, using transcriptomics. She is currently working with cutting-edge genomics tools to understand the evolutionary mechanisms generating color novelty in birds, both through natural and artificial selection.