PLUMAGE · Embryonic control of trends and variation in avian colour patterns

Most animals display striking patterns (i.e., spatial arrangement of characters in typical geometries). Natural patterns vary extensively, but also display trends within given taxa. A major biological challenge is to identify the pattern-forming events that shape this typical phenotypic landscape. Here, we propose to study the mechanisms responsible for the formation and evolution of the avian colour pattern (i.e., the spatial distribution of colour across the plumage). We test the provocative idea that despite enormous apparent diversity, variation in avian colour patterns is in fact very limited due to early developmental constraints, most variation resulting from colour choice changes in a common template. To test this hypothesis, we designed a step-wise approach organised in 4 specific research objectives: first, we will identify broadly shared and group-specific colour domains in the avian plumage by performing a quantitative survey across the entire bird phylogeny. Second, we will pinpoint the embryonic origin of these colour domains by constructing a lineage map of the developing skin. Third, we will identify positional cues controlling the establishment of embryonic blueprints of the future colour pattern by performing comparative expression analyses and functional tests in species displaying relevant pattern variation. Fourth, we will uncover changes in mechanisms through which embryonic blueprints implement the pattern in the late skin by pinpointing genetic loci co-evolving with pattern changes and testing their effect in an ex vivo system. In each objective, our methodology opportunistically uses non-model species of birds and robust functional testing performed in multiple species. Together, this proposal represents the largest comparative study of developmental processes undertaken in natural populations of birds. Results will provide a comprehensive understanding of the developmental mechanisms underlying trends and variation in natural patterns.