Comparative Phylogeography of Floreana's Lizards Supports Galápagos Pleistocene Paleogeographical Model and Informs Conservation Management Decisions
Terrestrial squamate reptiles from the Galápagos archipelago have limited gene flow among islands, which provides an opportunity to test paleogeographic models. Previous work suggests that Pleistocene glaciations had a strong influence on the evolution of Galápagos's sea-locked vertebrates by allowing dispersal and contact among populations from different islands through land connections for the last 700,000 yr. A prediction of the model is that extant populations, despite being isolated at present, are more genetically similar than would be expected given their age of origin due to recent (Pleistocene) gene flow. Based on mitochondrial genes, we test the prediction with a comparative phylogeographic analysis of two sympatric species of lizards (Microlophus grayii and Phyllodactylus baurii) from Floreana island and two surrounding islets. As expected by the paleogeographic model, lizards from Floreana are very similar genetically to conspecifics from Champion, which, unlike Gardner, was connected to Floreana during Pleistocene glacial maxima. Moreover, populations of Floreana and Champion do not share haplotypes, suggesting that genetic drift played an important role in their evolution. The split between Gardner and Floreana plus Champion populations was estimated at 0.99 million years ago (mya) for Lava Lizards and 3.41 mya for Leaf-toed Geckos, whereas the split between populations from Floreana and Champion was 0.72 and 2.43 mya, respectively. Our results also show that Floreana and Champion populations are part of the same evolutionarily significant unit for each species, which might be at risk due to an upcoming invasive mammal eradication program in Floreana. Therefore, Champion represents a reasonable source for potential reintroductions if necessary.ABSTRACT
Map of Floreana and surrounding islets showing study sites. Bathymetric contour lines delimit depths of 50 m (lighter blue), 100 m, 150 m, 200 m, and >200 m (darker blue). Inset map shows location of Floreana within the Galápagos archipelago.
Maximum-likelihood gene trees of Microlophus (left) and Phyllodactylus (right) from the Galápagos Islands. Numbers next to branches correspond to bootstrap support values; for clarity, numbers in short branches are not shown. Species names followed by voucher (new sequences) or GenBank accession number and collection island are presented. Specimens from Floreana are in red, Champion in green, and Gardner in blue.
Haplotype networks of Floreana Lava Lizards (A), (B) and Floreana Leaf-toed Geckos (C), (D) based on mitochondrial genes ND2 and ND4, respectively. Networks A and C include all sampled sequences, whereas B and D exclude sequences containing significantly more undefined states than others as calculated by PopART (Leigh and Bryant, 2015). Numbers next to branches are number of mutations among haplotypes. Black circles are inferred haplotypes. Localities in Floreana are Black Beach (BB), Puerto Velasco Ibarra (PVI) and Post Office Bay (POB).
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