Abstract
Patterns of colonization and diversification on islands provide valuable insights into evolutionary processes. Due to their unique geographic position and well known history, the Galapagos Islands are an important model system for evolutionary studies. Here we investigate the evolutionary history of a winged grasshopper genus to infer its origin and pattern of colonization in the Galapagos archipelago. The grasshopper genus Sphingonotus has radiated extensively in the Palaearctic and many species are endemic to islands. In the New World, the genus is largely replaced by the genus Trimerotropis. Oddly, in the Caribbean and on the Galapagos archipelago, two species of Sphingonotus are found, which has led to the suggestion that these might be the result of anthropogenic translocations from Europe. Here, we test this hypothesis using mitochondrial and nuclear DNA sequences from a broad sample of Sphingonotini and Trimerotropini species from the Old World and New World. The genetic data show two distinct genetic clusters representing the New World Trimerotropini and the Old World Sphingonotini. However, the Sphingonotus species from Galapagos and the Caribbean split basally within the Old World Sphingonotini lineage. The Galapagos and Caribbean species appear to be related to Old World taxa, but are not the result of recent anthropogenic translocations as revealed by divergence time estimates. Distinct genetic lineages occur on the four investigated Galapagos Islands, with deep splits among them compared to their relatives from the Palaearctic. A scenario of a past wider distribution of Sphingonotus in the New World with subsequent extinction on the mainland and replacement by Trimerotropis might explain the disjunct distribution.
Highlights
Oceanic archipelagos are natural laboratories for studying evolutionary processes [1]
The alignment for the NADH Dehydrogenase subunit 5 (ND5) fragment consisted of 955 bp and 104 sequences
For the nuclear Histone 3 (H3) gene fragment 293 bp were sequenced for the same set of taxa (Table 1)
Summary
Oceanic archipelagos are natural laboratories for studying evolutionary processes [1]. Its remote location far off the coast of Ecuador and its well-known geologic history [5] provide a unique opportunity to study colonization and subsequent radiation processes. The islands in their current state developed less than 5 million years ago [5, 6, 7]. The ages of the central and western islands, are much younger and range between 0.5 and 2.5 my [8]. This variation in island age might influence patterns of divergence within the archipelago
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