Many island archipelagos sit on shallow continental shelves, and during the Pleistocene, these islands were connected as global sea levels dropped following glaciation. The way these now extinct 'paleo-islands' influenced historic gene flow is relevant for interpreting contemporary patterns of genetic diversity in island species. Sherlock et al. (2025) studied the Frigate Island Caecilian, Hypogeophis rostratus, a direct-developing caecilian amphibian found on 10 islands in the granitic Seychelles archipelago. Using fine-scale genomic data (ddRADseq), they found that genomic clusters often did not correspond to islands in the archipelago and that isolation-by-distance patterns were more consistent with gene flow across a continuous landscape than with isolated island populations. Based on several population genomic analyses, they found that present-day biogeographic patterns are likely related to signals from extinct Pleistocene landmasses. This suggests that the signatures of gene flow associated with paleo-islands may be stronger than the isolating effects of contemporary islands in terrestrial species distributed on continental shelf islands.

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