Exploring the combined role of eustasy and oceanic island thermal subsidence in shaping biodiversity on the Galapagos

Aim We constructed a series of high-resolution palaeogeographical models for the Galapagos archipelago for the last 700kyr, accommodating thermal subsidence of the islands, eustatic sea-level change, and associated sea-floor loading. We assessed the possible impacts of these changes for the terrestrial fauna. Location The Galapagos Islands. Methods Palaeogeographical modelling and evaluation of biogeographical distributions. Results Since 700 ka, sea levels broadly similar to those today isolated the various Galapagos islands for intervals of c. 90kyr. Intervening 5-10kyr periods of extreme lowstands in sea level (-140 to -210m) dramatically changed the central and western archipelago, with several large islands, plus their satellites, coalescing. During the several connection episodes the land-locked vertebrates had significant or complete access to all of the newly exposed terrain. Analysis of the biological data suggests that these physical processes left detectable imprints on the biogeography of groups including racer snakes, lava lizards, land iguanas and leaf-toed geckos. Main conclusions In the recent geological past, a sizeable region within the Galapagos chain must have experienced rapid, significant changes in its geography as a result of major shifts in local relative sea level periodically connecting and then isolating islands. This might explain striking patterns in the distribution and composition of the archipelago's land fauna. These insights provide a platform for future studies predicting the ages of subpopulation separations, which should correspond to the sea-level rises that followed each of the lows. The oscillating geography mechanism described herein may provide a new lens to view biological evolution on a number of other island chains, including the Maldives, the Canaries and Cape Verde.