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Tiny Wrens Evolve Big on Remote Scottish Islands
2 Jun
Summary
- Island wrens on Shetland and St Kilda exhibit gigantism, growing twice as large.
- Each of four isolated island wren populations shows genetic distinctiveness.
- Parallel evolution drives similar traits in island wrens through different genetic paths.
Wrens inhabiting remote Scottish islands are providing a clear view of evolution. Researchers have documented significant changes in several isolated island populations, with birds on Shetland and St Kilda exhibiting striking "island gigantism," becoming much larger than their mainland counterparts. These island wrens typically weigh approximately 13 to 16 grams, compared to the 7 to 10 grams of British mainland wrens.
Each of the four island groups studied—Shetland, Fair Isle, the Outer Hebrides, and St Kilda—is genetically distinct from mainland birds. Shetland and St Kilda wrens show the most pronounced differences in appearance and song. This research highlights parallel evolution, where similar environmental pressures independently lead to similar traits like increased size, but through different genetic pathways.
The study used body measurements, song recordings, and genome sequencing to compare island wrens with mainland birds. The genetic data confirmed that each island population is largely isolated and that even wrens with similar physical traits evolved their size via distinct genetic changes. This makes these wrens a powerful model for understanding how biodiversity forms and species diverge globally.
