A molecular phylogenetic analysis of the Oedipodinae and their intercontinental relationships

Oedipodine grasshoppers occur throughout the major continents, making them the most widely distributed of the 30 subfamilies that comprise the Acrididae. Most species have been allocated to one of 15 tribes; some remain unassigned. The subfamily, according to Vickery, had an ancient origin, just after the breakup of Pangaea but before the separation of Laurasia from Africa. Thereafter, Oedipodinae continued to evolve in separate continental centers; some Nearctic species apparently descended more recently from Palearctic ancestors when land bridges still connected the two continents.Our objectives are to independently assess these biogeographic accounts, to examine the validity of several tribal constructs, and to shed light on problematic taxa such as Stethophyma and Machaerocera which have had, over the years, an ambivalent affiliation with Oedipodinae. To realize these goals, we sequenced and phylogenetically analyzed portions of four mitochondrial genes (coding for cytochrome oxidase subunits I and II, cytochrome b, and NADH dehydrogenase subunit V), totaling up to 2254 bp, in specimens collected in the Americas, Eurasia, Africa and Australia. Methodology entailed applying weighted and unweighted maximum parsimony, maximum likelihood and Bayesian techniques. A member of the Pyrgomorphidae served as the outgroup. The ages of evolutionary divisions were estimated using the program "r8s"; the date of 100 Mya, previously estimated as the time of divergence between the subfamilies Oedipodinae and Gomphocerinae, was used to calibrate our chronogram.In general, taxa appear to assort themselves according to continental land mass, rather than by tribe. Aiolopini, Bryodemini, Oedipodini and Sphingonotini proved to be nonmonophyletic, whereas there was no evidence to reject monophyly in Acrotylini, Chortophagini, Locustini and Psinidini. Phylogenetically, both Machaerocera and Stethophyma were well-positioned within the Oedipodinae, with Machaerocera closely aligned with Chortophaga and Encoptolophus, and Stethophyma tightly linked to Aiolopus. Duroniella, presently regarded as an oedipodinid, emerged strongly connected to the Gomphocerinae.The current biogeographical distribution of Oedipodinae is the result of widespread intercontinental dispersion. In particular, with the assistance of DIVA analysis, we argue that Asiamerica was the center of initial oedipodinid radiation about 94 Mya. Through a series of early dispersals, the remaining clusters of taxa were established. Somewhat surprisingly, this includes the branch leading to the Australian genera Austroicetes and Chortoicetes. In contrast, the multiple dispersals to the African continent occurred more recently. It would appear that North American oedipodinids had both an ancient and a more recent ancestry. The single South American species analyzed evolved very recently from North American ancestors.

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