open access publication

Article, 2023

Population genomics of the island thrush elucidates one of earth’s great archipelagic radiations

In: Evolution Letters, ISSN 2056-3744, Volume 7, 1, Pages 24-36, 10.1093/evlett/qrac006

Contributors (14)

Reeve, Andrew Hart (Corresponding author) [1] Gower, Graham (0000-0002-6197-3872) [1] Pujolar, Jose Martin [1] [2] Smith, Brian Tilston [3] Petersen, Bent Ole (0000-0002-2472-8317) [1] [4] Olsson, Urban [5] Haryoko, Tri (0000-0002-8549-3662) [6] Koane, Bonny (0000-0001-6770-5126) [7] [8] Maiah, Gibson [8] Blom, Mozes Pil Kyu (0000-0002-6304-9827) [9] Ericson, Per G P (0000-0002-4143-9998) [10] Irestedt, Martin (0000-0003-1680-6861) [10] Racimo, Fernando (0000-0002-5025-2607) [1] Jønsson, Knud Andreas (0000-0002-1875-9504) [1]


  1. [1] University of Copenhagen
  2. [NORA names: KU University of Copenhagen; University; Denmark; Europe, EU; Nordic; OECD]
  3. [2] Technical University of Denmark
  4. [NORA names: DTU Technical University of Denmark; University; Denmark; Europe, EU; Nordic; OECD]
  5. [3] American Museum of Natural History
  6. [NORA names: United States; America, North; OECD]
  7. [4] Asian Institute of Medicine, Science and Technology
  8. [NORA names: Malaysia; Asia, South]
  9. [5] University of Gothenburg
  10. [NORA names: Sweden; Europe, EU; Nordic; OECD]


Tropical islands are renowned as natural laboratories for evolutionary study. Lineage radiations across tropical archipelagos are ideal systems for investigating how colonization, speciation, and extinction processes shape biodiversity patterns. The expansion of the island thrush across the Indo-Pacific represents one of the largest yet most perplexing island radiations of any songbird species. The island thrush exhibits a complex mosaic of pronounced plumage variation across its range and is arguably the world's most polytypic bird. It is a sedentary species largely restricted to mountain forests, yet it has colonized a vast island region spanning a quarter of the globe. We conducted a comprehensive sampling of island thrush populations and obtained genome-wide SNP data, which we used to reconstruct its phylogeny, population structure, gene flow, and demographic history. The island thrush evolved from migratory Palearctic ancestors and radiated explosively across the Indo-Pacific during the Pleistocene, with numerous instances of gene flow between populations. Its bewildering plumage variation masks a biogeographically intuitive stepping stone colonization path from the Philippines through the Greater Sundas, Wallacea, and New Guinea to Polynesia. The island thrush's success in colonizing Indo-Pacific mountains can be understood in light of its ancestral mobility and adaptation to cool climates; however, shifts in elevational range, degree of plumage variation and apparent dispersal rates in the eastern part of its range raise further intriguing questions about its biology.


Greater Sundas, Guinea, Indo-Pacific, Islands region, Mountains, New Guinea, Philippines, Pleistocene, Polynesia, SNP data, Sunda, Wallacea, adaptation, ancestor, archipelago, biodiversity patterns, biology, birds, climate, colonization, complex mosaic, comprehensive sampling, cool climate, data, degree, demographic history, dispersal rates, eastern part, elevational range, evolutionary studies, expansion, flow, forest, gene flow, genome-wide SNP data, genomics, globe, history, ideal system, instances, intriguing question, island radiations, islands, laboratory, light, lineage radiation, mask, mobility, mosaic, mountain forests, natural laboratory, numerous instances, part, path, patterns, phylogeny, plumage variation, population, population genomics, population structure, quarter, questions, radiation, range, rate, region, sampling, sedentary species, shift, songbird species, speciation, species, structure, study, success, system, thrush, thrush populations, tropical archipelago, tropical islands, variation, world


  • Directorate for Biological Sciences
  • Knut and Alice Wallenberg Foundation
  • Carlsberg Foundation
  • Swedish Research Council
  • Novo Nordisk Foundation
  • Novo Nordisk (Denmark)
  • The Velux Foundations