ORIGIN OF NOVEL COLOR PHENOTYPES: CONTRIBUTION OF STRUCTURAL PROPERTIES OF BIOCHEMICAL NETWORKS

Abstract

Examining the phenotypic variation observed within a species is an opportunity to understand the evolutionary stability and potential evolutionary trajectories of the species. Feather coloration in many birds is produced by complex biochemical networks that modify ingested, dietary carotenoids to produce colorful carotenoids deposited into feathers. Within-species color variation can be caused by variation in either the structure of this network or the flux through it. Here we tested the contribution of structural properties of biochemical networks to variation across individuals from 21 populations of house finches (Haemorphous mexicanus) in recently established populations in Montana and ancestral populations in Arizona. With the largest carotenoid networks of any studied species, the house finch provides an ideal system to address how population-specific utilization of biochemical networks contributes to population divergence in coloration. Using high performance liquid chromatography, we extracted and identified the carotenoid compounds from over 3,000 feather samples representing 1,000 individuals. We analyzed the relationship between the presence of different compounds across populations and their topological positions within the network. We then tested whether populations diverge along the same or different pathways within the network. We found that derived carotenoids contributed more to population divergence compared to dietary carotenoids, suggesting that evolution of biochemical synthesis accompanied recent population divergence in ecologically distinct locations.