Doctor of Philosophy (PhD)


Biological Sciences

Document Type



I address the evolution of drab bird colors at micro- and macroevolutionary scales. I use as a study system the Furnariida, a clade of >600 Neotropical passerine species that, despite tremendous ecological and morphological diversity, are colored almost exclusively in shades of brown and grey produced by melanin pigments.

In chapters two and three, I took a macroevolutionary approach and showed that (1) plumage colors in the Furnariida evolve at similar rates in a monochromatic clade, males of a dichromatic clade, and females of a dichromatic clade; (2) ventral plumage color evolves faster than dorsal; (3) bird species that occupy darker habitats tend to be darker-colored; (4) that plumage color in the Furnariidae (a family within Furnariida) only partially conforms to Gloger’s rule, a classic ecogeographical principle relating animal color to climate; and (5) that the effects of light environments and climate on plumage color persist even after controlling for one another.

In chapter four, I started focusing on one species, the Variable Antshrike (Thamnophilus caerulescens, Thamnophilidae), which is widely distributed in South America and presents impressive plumage color variation, including hybrids with intermediate colors. I developed an index to quantify the magnitude of intraspecific plumage color variation, and used it to show that the Variable Antshrike is exceptionally variable compared to other thamnophilids.

In chaper five, I addressed Gloger’s rule in the Variable Antshrike. I showed that that species follows the predictions that (1) birds should be darker in rainier areas, (2) birds should be redder in drier areas, and (3) birds should be redder in warmer areas. But it does not follow the Gloger’s rule prediction that birds should be darker in warmer areas.

Finally, in chapter six, I re-sequenced the genomes of 115 Variable Antshrike individuals and performed divergence scans to characterize the landscape of genomic differentiation among hybridizing subspecies. I found a highly-differentiated region on chromosome 17 that might contain a regulatory element of ASIP, a gene involved in color variation in other birds and mammals.



Committee Chair

Brumfield, Robb T

Available for download on Monday, March 11, 2024