Evolutionary mechanisms in the postglacial radiation of the songbird genus Junco: a population-genomic approach

• Autores: Javier Sala García
• Directores de la Tesis: Borja Milà Valcárcel (dir. tes.), José Luis Bella Sombría (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2026
• Idioma: inglés
• Número de páginas: 228
• Materias:
  • Ciencias de la vida
    • Genética
      • Ingeniería genética
    • Paleontología
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • Understanding how new species arise, from initial population divergence to the evolution of reproductive isolation, remains a central goal in evolutionary biology. Disentangling the roles of demographic history and natural selection at early stages of divergence is particularly challenging, and young, geographically widespread lineages offer unique insights into this process. The North American songbird genus Junco, which underwent a rapid postglacial radiation and exhibits extensive geographic and phenotypic variation, provides an ideal system for studying incipient speciation, particularly the dark-eyed junco (Junco hyemalis). In order to disentangle the contributions of demographic history and natural selection during incipient divergence, the aims of this thesis are: (i) to reconstruct the evolutionary and demographic history across the Junco genus; (ii) to identify genomic regions under selection associated with trait divergence; (iii) to evaluate how recombination and natural selection interact to shape genomic differentiation; and (iv) to test how genetic drift, gene flow, and environmental variation interact in a young, spatially structured lineage. Genomic, SFS- and coalescent-based demographic modeling, together with paleodistribution analyses, indicate that Junco underwent a rapid postglacial expansion, resulting in shallow phylogenetic splits, pervasive incomplete lineage sorting, and evidence of recent secondary contact among lineages. Moreover, the pronounced mitonuclear discordance observed among southern Junco lineages can be explained by sexbiased dispersal or historical mitochondrial capture. Across the genome, most heterogeneity in differentiation is attributable to variation in recombination rate and linked background selection, but clear signals of positive selection are also evident, particularly at loci affecting plumage and iris coloration. In addition, a large polymorphic inversion on chromosome 5 recurs as a major axis of differentiation, shows a pronounced latitudinal cline and sweep-like signals near putative breakpoints, and, given its functional enrichments, is consistent with a possible role in seasonal timing and migratory physiology. Finally, a fine-scale analysis across a narrow contact zone between lineages reveals that environmental divergence can persist despite ongoing gene flow, offering a microgeographic perspective on the interplay of selection and drift in this young radiation. Together, these findings demonstrate the value of combining demographic inference, trait mapping, and recombination-aware genomic scans to illuminate the genomic basis of divergence at its earliest stages