Selection on a single locus drives plumage differentiation in the Rufous-collared Sparrow (Zonotrichia capensis)

Area of Science:

• Evolutionary Biology
• Genomics
• Ornithology

Background:

• The Rufous-collared Sparrow (Zonotrichia capensis) exhibits significant phenotypic variation across its range.
• The Patagonian subspecies, Z. c. australis, is notably distinct with a grey head and paler plumage, lacking typical crown stripes.

Purpose of the Study:

• To investigate the genomic underpinnings of plumage color differences in Zonotrichia capensis.
• To explore the evolutionary mechanisms driving the distinct phenotype of the Z. c. australis subspecies.

Main Methods:

• Whole-genome sequencing of 18 Rufous-collared Sparrow individuals (9 Z. c. australis and 9 from northern Argentina).
• Analysis of genomic differentiation, focusing on a specific divergence peak on chromosome 5.
• Mitochondrial DNA analysis to estimate divergence times.

Main Results:

• A single ~465-kb genomic divergence peak was identified on chromosome 5, containing the ST5 gene.
• ST5 regulates RAB9A, a gene crucial for melanosome biogenesis and pigmentation.
• Mitochondrial DNA suggests Z. c. australis diverged approximately 400,000 years ago, potentially influenced by Pleistocene glaciations.

Conclusions:

• The ST5 gene is a strong candidate for the melanic plumage polymorphism in Zonotrichia capensis.
• The observed plumage differences align with Gloger's rule, correlating lighter coloration with colder, drier climates.
• Genomic differentiation may result from selection in allopatric populations or selection against gene flow.