CORRESPONDENCE BETWEEN STRUCTURAL AND DYNAMIC PROPERTIES IN A BIOCHEMICAL NETWORK

Abstract

Phenotypic traits are determined by networks of interactions between genes, proteins and enzymes. Structural positions of regulatory mechanisms in the network can determine variability in its elements. Here we examine the topological properties of controls that regulate element expression in a network. If distinct regulatory controls are located at the beginning and end of the same pathway, then we would expect phenotypic differences to be due to differences in the pathway length of their respective networks. Alternatively, if each pathway has its own control mechanism, then phenotypic differences would be the result of differences in the connection density of pathways present in each network. It is also possible that regulatory mechanisms are independent of the network structure, and if this is the case phenotypic differences would not be related to structural properties of the network. To test these hypotheses we extracted carotenoid compounds from the feathers of 59 female house finches (Haemorhous mexicanus) from Arizona and Montana and constructed carotenoid metabolic networks for each individual. We examined whether the highly variable expression of carotenoids in female feathers is caused by differences in the expression of carotenoids as the result of the gain or loss of compounds within the same pathway or among distinct pathways. We find that most of the differences between individuals were caused by differences in which pathways were expressed and not by differences in the elongation of the same pathway. These findings enhance our understanding of biochemical mechanisms that underlie avian carotenoid coloration diversification.