Subfamilies Acridinae, Gomphocerinae and Oedipodinae are “Fuzzy Sets”: A Proposal for a Common African Origin

We propose that subfamilies Acridinae (including Truxalinae), Gomphocerinae and Oedipodinae are not monophyletic, and that, as a collective, originated in Africa some time before 100 mya.Our conclusions are based on a phylogenetic analysis of portions of 5 mitochondrial genes, totalling up to about 2.7 kilobase pairs, in 117 species collected in the Americas, Eurasia, Africa and Australia. Sequences were analyzed by weighted and unweighted maximum parsimony, maximum likelihood and Bayesian methods. Pyrgomorpha conica served as the outgroup. Biogeographic origins and patterns were inferred by applying the programs “DIVA” and “r8s”, for spatial and temporal analyses, respectively.Maximum sorting of taxa using parsimony was achieved by assigning differential weights to the three codon positions. Resolution was, however, generally poor. Bayesian methods, by contrast, yielded a topology which was virtually identical to the maximum likelihood tree and, for the most part, fully resolved and interpretable. We provide arguments in support of favoring the use of the Bayesian tree to infer relationships and biogeographic origins.Neither subfamily, as defined in the current on-line Orthoptera Species File 2, proved to be monophyletic. Instead, taxa assorted themselves into 3 broad categories: 1) Gomphocerinae, plus a small subset of acridines; 2) a sister group consisting of Oedipodinae, plus another small subset of acridines; and basal and paraphyletic to this pair, 3) the remaining taxa, all African and primarily members of the Acridinae. Very few tribes within these subfamilies proved to be monophyletic.This phylogenetic pattern is reflected biogeographically and points to a common African origin for the subfamilies. The following migrations, initially those of (most likely) proto-acridines, are further suggested by the data: 1) movement from Africa to South America establishing genera of that continent's Gomphocerinae (e.g., Jagomphocerus) and Acridinae (e.g., Metaleptea), followed by incursions into North America, leading to species such as Amblytropidia mysteca; 2) a somewhat circuitous sequence of events involving a reverse migration from South America to Africa (establishing genera such as Thyridota) with ensuing dispersals to Eurasia (forming genera such as Myrmeleotettix) and to North America (leading to, for example, Brunneria and the bulk of that continent's Gomphocerinae); 3) almost simultaneous with the first event, migration of other early acridines from Africa to Eurasia, establishing the latter continent's Oedipodinae (e.g., Angaracris). Subsequent dispersals to North America and the South Pacific led to genera such as Camnula and Austroicetes, respectively.

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