Bacteria and the evolution of honest signals. The case of ornamental throat feathers in spotless starlings

1.Mechanisms guaranteeing reliability of messages are essential in understanding the underlying information and evolution of signals. Microorganisms may degrade signalling traits and therefore, influence the transmitted information and evolution of these characters. The role of microorganisms in animal signalling has, however, rarely been investigated.

2.Here, we explore a possible role for feather-degrading bacteria driving the design of ornamental throat feathers in male spotless starlings (Sturnus unicolor). We estimated length, bacterial load, degradation status, and susceptibility to degradation by keratinolytic bacteria in those feathers, compared to non-ornamental adjacent feathers in males, as well as to throat feathers in females. In addition, the volume of the uropygial gland and its secretion was measured, and the secretion extracted. We also experimentally evaluated the capacity of each secretion to inhibit growth of a keratinolytic bacterium.

3.The apical part of male...