Mitochondrial gene rearrangements are the latest tool in the arsenal of phylogeneticists for investigating historical relationships. They are complex molecular characters that may provide more reliable evidence of ancestry than comparative molecular data. Here we review the phylogenetic utility of mitochondrial gene rearrangements, and find that despite isolated incidences of convergence, derived gene order appears highly congruent with phylogenies produced from other sources of data. We calculate that the chance of two mitochondrial genomes sharing the same derived genome organisation is only 1/2664, but caution that this ignores the possibility that the (as yet uncharacterised) gene rearrangement mechanism may greatly increase the chance of convergence. Broader taxonomic surveys of mitochondrial genome organisation will lead to a more realistic indication of the historical incidence of convergence in genome organisation.
We characterized the organization of mitochondrial genes from a diverse range of hymenopterans. Of the 21 taxa characterized, 12 had distinct, derived organizations. Some rearrangements were consistent with the duplication-random loss mechanism, while others were not. Local inversions were relatively common, i.e., rearrangements characterized by the movement of genes from one mitochondrial strand to the other, opposite or close to their ancestral position. This type of rearrangement is inconsistent with the duplication/random loss model of mitochondrial gene rearrangement. Instead, they are best explained by the operation of recombination. Taxa with derived organizations were restricted to a single, monophyletic group of wasps, the Apocrita, which comprise about 90% of all hymenopterans.
The Platygastroidea are a diverse group of mostly small to tiny wasps, the common biology for which is endoparasitism of insect and spider eggs. No analytically-based phylogeny exists for the superfamily, and the current suprageneric classification is flawed in part because of its reliance on homoplasious and pleisiomorphic morphological characters. To determine platygastroid relationships as a basis for investigating host and ovipositor evolution, phylogenies of > 70 in-group species (representing 55 genera) were reconstructed by parsimony and Bayesian methods using three molecular markers; the mitochondrial cytochrome oxidase I and the nuclear genes 28S and 18S rRNA . The results strongly support the monophyly of the superfamily and one of the two families, Platygastridae, but the Scelionidae are most likely polyphyletic. However, within the Scelionidae, there is a well supported 'main scelionid clade' that contains the majority of genera assigned to the family. At the subfamilial level, both putative subfamilies of Platygastridae, the Platygastrinae, and Sceliotrachelinae, are likely to be polyphyletic. Within the Scelionidae, both the Teleasinae and Telenominae are monophyletic, but the Scelioninae is clearly not so. The current tribal classification for the Scelionidae is in need of major reassessment because no tribes, with the exception of the Scelionini s.s ., were found to be monophyletic. Further illustrating the problems associated with the current classification is the nonmonophyly of a number of genera, namely Opisthacantha Caloteleia , Telenomus , Trimorus , Teleas and Idris. Analysis of ovipositor evolution in the superfamily revealed that the Ceratobaeus -type ovipositor system is ancestral; however, this trait was lost prior to the evolution of the main scelionid clade, for which the Scelio -type ovipositor system is ancestral and defines a mostly paraphyletic assemblage. Ancestral state analysis indicates that the Ceratobaeus -type ovipositor was subsequently re-evolved in the main scelionid clade, representing a possible contradiction of Dollo's law. Previously, the tribal placement has been used to predict the host associations of genera for which host data were unavailable. However, the fact that most tribes are not monophyletic throws into doubt any such speculation based on the current classification.
We investigated the putative association between the parasitic lifestyle and an accelerated rate of mt genetic divergence, compositional bias, and gene rearrangement, employing a range of parasitic and nonparasitic Diptera and Hymenoptera. Sequences were obtained for the cox1, cox2, 16S, 28S genes, the regions between the cox2 and atp8 genes, and between the nad3 and nad5 genes. Relative rate tests indicated generally that the parasitic lifestyle was not associated with an increased rate of genetic divergence in the Diptera but reaffirmed that it was in the Hymenoptera. Similarly, a departure from compositional stationarity was not associated with parasitic Diptera but was in parasitic Hymenoptera. Finally, mitochondrial (mt) gene rearrangements were not observed in any of the dipteran species examined. The results indicate that these genetic phenomena are not accelerated in parasitic Diptera compared with nonparasitic Diptera. A possible explanation for the differences in the rate of mt molecular evolution in parasitic Diptera and Hymenoptera is the extraordinary level of radiation that has occurred within the parasitic Hymenoptera but not in any of the dipteran parasitic lineages. If speciation events in the parasitic Hymenoptera are associated with founder events, a faster rate of molecular evolution is expected. Alternatively, biological differences between endoparasitic Hymenoptera and endoparasitic Diptera may also account for the differences observed in molecular evolution.
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