Meeting Abstract
Visual ornaments have evolved in a wide range of taxa to convey information about quality and condition. Ornamentation can be found in both sexes in birds, and comparative work shows that sexual dichromatism can arise due to changes in both male and female colors. However, many questions remain about the underlying mechanisms of ornament evolution and how these may act to promote or constrain evolutionary pattern and tempo. We contrast the anatomical basis for variation in a plumage-based signal in three lineages of Malurus fairywrens (family Maluridae) using a combination of photospectroscopy and electron microscopy. We focus on melanin-based color in two subspecies of Malurus alboscapulatus (WSFW: White-shouldered Fairywren), that differ in degree of female ornamentation, and Malurus melanocephalus (RBFW: Red-backed Fairywren) that exhibits within year variation in male ornamentation. We leveraged these patterns of variation to assess how changes in feather morphology mediate changes in visual signal expression within and among sexes of these two closely related species. First, we ask how males and females differ in color and feather structure and compare ornamented and unornamented female in the WSFW. Next, we assess mechanisms of production in RBFW, but instead by focusing on comparing ornamented and unornamented males to unornamented females. Our over-arching, null hypothesis was that ornamentation is produced through similar changes in barbule density and fine scale arrangement of melanin in barbules across all sexes and species. We find that females produce an ornament unique from males that corresponds to differences in underlying feather structure characteristics. In contrast, in the RBFW we found similarity between unornamented males and unornamented females in color and feather structure.
