ISLAND BIOGEOGRAPHY OF GALÁPAGOS LAVA LIZARDS (TROPIDURIDAE:MICROLOPHUS): SPECIES DIVERSITY AND COLONIZATION OF THE ARCHIPELAGO

Abstract

The "lava lizards" (Microlophus) are distributed throughout the Galápagos Archipelago, and consist of radiations derived from two independent colonizations. The "Eastern Radiation" includes M. bivittatus and M. habeli endemic to San Cristobal and Marchena Islands. The "Western Radiation" includes five to seven historically recognized species distributed across almost the entire Archipelago. We combine dense geographic sampling and multilocus sequence data to estimate a phylogenetic hypothesis for the Western Radiation, to delimit species boundaries in this radiation, and to estimate a time frame for colonization events.Our phylogenetic hypothesis rejects two earlier topologies for the Western Radiation and paraphyly of M. albemarlensis, while providing strong support for single colonizations on each island. The colonization history implied by our phylogeny is consistent with general expectations of an east-to-west route predicted by the putative age of island groups, and prevailing ocean currents in the Archipelago. Additionally, combined evidence suggests that M. indefatigabilis from Santa Fe should be recognized as a full species. Finally, molecular divergence estimates suggest that the two colonization events likely occurred on the oldest existing islands, and the Western Radiation represents a recent radiation that, in most cases, has produced species that are considerably younger than the islands they inhabit. K E Y W O R D S :Galápagos, lizards, mitochondrial DNA, molecular timing of colonization, nuclear DNA, oceanic islands, phylogeny.Oceanic islands have been model systems in evolutionary studies for well over a century (Emerson 2002;Whittaker et al. 2008), and the Galápagos Archipelago, located about 960 km west from the coast of Ecuador, has figured prominently among them. Galápagos is one of the most recent oceanic island formations (Christie et al. 1992), and a consensus biogeographic history (reviewed in Grehan 2001) has favored an over-water colonization model for the origin of its many endemic radiations. Most of these studies have emphasized early models of Galápagos colonization events that were initially constrained to a 4 to 5 million year time frame set by the estimated ages of the oldest current islands (Cox 1983). The subsequent discovery of underwater seamounts representing former Galápagos islands to the east of the current archipelago on the east-shifting Nazca Plate, extended the 1 6 0 6

Progressive colonization and restricted gene flow shape island-dependent population structure in Galápagos marine iguanas (Amblyrhynchus cristatus)

“…The microsatellite loci data therefore suggest that the structuring of marine iguana populations generally follows a pattern of one genetic unit per island. A similar pattern was also recently demonstrated for Galápagos lava lizards from the genus Microlophus [71]. …”

Older than the islands: origin and diversification of Galápagos leaf‐toed geckos (Phyllodactylidae: Phyllodactylus) by multiple colonizations

“…Nonetheless, this does not invalidate the vicariance scenario, because a large island, where the volcanoes that later formed the central and western islands emerged, was probably present at that time. These palaeogeographical studies challenge traditional, dispersal‐based biogeographical reconstructions for other terrestrial organisms in the Galápagos Islands, such as the lava lizards (Benavides et al ., ; Geist et al ., ) and giant tortoises (Caccone et al ., ; Poulakakis et al ., ), and highlight the importance of considering both dispersal and vicariance in the interpretation of biogeographical patterns on oceanic islands.…”

“…The intervals between colonization events differ strongly, however, between lava lizards and leaf‐toed geckos. Lava lizards colonized the archipelago twice within a 2.5‐Myr period (Benavides et al ., ), whereas the two colonization events by leaf‐toed geckos reported in this paper are 10 Myr apart (Table ). Multiple colonizations have been detected among Galápagos plants (Andrus et al ., ) and, although rare, they form part of the biogeography of other oceanic islands worldwide, such as Hawaii, the Society Islands, the Marquesas Islands and the Canary Islands (Juan et al ., ; Cowie & Holland, ; Gillespie et al ., ).…”

Inference of Population History by Coupling Exploratory and Model-Driven Phylogeographic Analyses

“…Despite the potential utility of molecular dating for examining temporal concordance among inferences of population growth or vicariance, which is a particularly promising endeavor when several external calibration points are available [152,159,168], caution is still warranted. Time-dependency of molecular rates can have non-negligible impacts on the accuracy of divergence dates estimated using intraspecific DNA sequence datasets [169,170], and the timescales that are most relevant to population-level studies occupy a critical region of the time-dependency curve.…”