Evolution of plumage patterns in pattern morphospace: A phylogenetic analysis of melanerpine woodpeckers

Plumage patterns of melanerpine (Melanerpes-Sphyrapicus) woodpeckers are strikingly diverse. Understanding the evolution and function of this diversity is challenging due to the difficulty of quantifying plumage patterns. We use a 3-dimensional space to characterize the evolution of melanerpine achromatic plumage patterns. The axes of the space are three pattern features (spatial frequency, orientation, and contrast) quantified using 2-dimensional fast Fourier transformation of museum specimen images. Mapping plumage in pattern space reveals differences in how species and subclades occupy the space. To quantify these differences, we derive two new measures of pattern: “pattern diversity” (diversity across plumage patches within a species) and “pattern uniqueness” (divergence of patterns from those of other species). We estimate that the melanerpine ancestor had mottled plumage and find that pattern traits across patches and subclades evolve at different rates. We also find that smaller species are more likely to display horizontal face patterning. We promote pattern spaces as powerful tools for investigating animal pattern evolution.

Methods
The photographs were collected with a Nikon D7000 camera and have been converted from .nef file format to .ppm format for use in MATLAB.