Sampling and laboratory protocols
We sampled tail tips of 29 specimens of the Floreana lava lizard and 33 of the Floreana leaf-toed gecko from Floreana (n = 10 and 10, respectively), Champion (n = 9 and 10), and Gardner (n = 10 and 13) islands in August 2018. In addition to the newly generated DNA sequences, we obtained from GenBank sequences of taxa belonging to the same radiations as M. grayii and P. baurii , with M. occipitalis and P. reissii , respectively, as outgroups (Benavides, Baum, Snell, Snell, & Sites, 2009; Torres-Carvajal et al., 2014). Lava lizards were captured by noosing or by hand, while geckos were captured by hand. Samples were stored in Longmire buffer. Floreana island (173 km2) lies in the south of the Galápagos archipelago; the islet of Champion (0.094 km2) lies 700 m NE of Floreana, whereas Gardner (0.81 km2) lies 8 km E of Floreana (Fig. 1). Maximum sea depth between Floreana and these islets is 50 m and 200 m, respectively.
We generated novel DNA sequences of NADH dehydrogenase subunit 2
(ND2) for lava lizards and NADH dehydrogenase subunit 4 (ND4) for leaf-toed geckos (Genbank accession numbers to be provided) following published protocols (Kizirian, Trager, Donnelly, & Wright, 2004; Torres-Carvajal, Barnes, Pozo‐Andrade, Tapia, & Nicholls, 2014).