Colonization and diversification of Galápagos terrestrial fauna: a phylogenetic and biogeographical synthesis

Abstract

Remote oceanic islands have long been recognized as natural models for the study of evolutionary processes involved in diversification. Their remoteness provides opportunities for isolation and divergence of populations, which make islands remarkable settings for the study of diversification. Groups of islands may share a relatively similar geological history and comparable climate, but their inhabitants experience subtly different environments and have distinct evolutionary histories, offering the potential for comparative studies. A range of organisms have colonized the Galápagos Islands, and various lineages have radiated throughout the archipelago to form unique assemblages. This review pays particular attention to molecular phylogenetic studies of Galápagos terrestrial fauna. We find that most of the Galápagos terrestrial fauna have diversified in parallel to the geological formation of the islands. Lineages have occasionally diversified within islands, and the clearest cases occur in taxa with very low vagility and on large islands with diverse habitats. Ecology and habitat specialization appear to be critical in speciation both within and between islands. Although the number of phylogenetic studies is continuously increasing, studies of natural history, ecology, evolution and behaviour are essential to completely reveal how diversification proceeded on these islands.

Hybridization masks speciation in the evolutionary history of the Galápagos marine iguana

“…Amblyrhynchus and Conolophus diverged around 4.5 Ma (figure 1b), whereas previous estimates based solely on mtDNA [22] suggested a much older divergence of around 10 Ma on the nowsunken islands of the archipelago. Our results reconcile Galápagos iguana divergence with the geological age of the oldest extant islands (Españ ola and San Cristó bal; figure 1b) and are consistent with similar estimates for other Galá pagos fauna [12], including giant tortoises (3- [21] and the earlier coalescence time of mtDNA [46] might account for these betweenmarker differences. Regardless of the discrepancy, divergences within Amblyrhynchus are remarkably recent, especially …”

“…It consists of 20 islands ranging from 1.6 to 4600 km 2 in size, plus numerous smaller islets, with ages of emergence dating back 0.06-4.0 Myr [11]. This archipelago has been colonized by many taxa, progressively from older to younger islands, with subsequent speciation, but also hybridization and gene flow between islands [12]. The various effects of hybridization have been documented in Darwin's finches, which represent one of the best-studied adaptive radiations worldwide [13].…”

Comparative phylogeography of oceanic archipelagos: Hotspots for inferences of evolutionary process

“…This spatial arrangement implies a potential diversification sequence from southeast to northwest, paralleling the geological formation of the archipelago's islands (58). Some lineages in the Galapagos show a very clear progression from older to younger islands (59), well illustrated by the Galapagos giant tortoise (Geochelone nigra), in which both the species-level phylogeographic pattern based on mtDNA data and the pattern of lineage sorting suggest diversification in parallel with the island geological formation (60,61 geological formation of island clusters of similar age (64). Among marine iguanas (Amblyrhynchus cristatus), mtDNA shows population differentiation concordant with geographical isolation of populations across the archipelago, a result largely in agreement with nuclear microsatellite data (65).…”

Investigating the origin of vagrant dusky groupers, Epinephelus marginatus (Lowe, 1834), in coastal waters of Réunion Island

“…Understanding cases of colonization of isolated volcanic islands through long distance dispersal provides insight into founding events and diversification that are fundamental processes underlying oceanic island endemism (Cowie & Holland, 2008;Parent et al, 2008). These oceanic islands are often distant from large land masses and the chance of colonization and subsequent divergence of populations is dependent on several biological and physical factors.…”