Mitochondrial cytochrome oxidase I in tetranychid mites: A comparison between molecular phylogeny and changes of morphological and life history traits

Spider mites, Tetranychidae, represent one of the most cosmopolitan and economically important groups of terrestrial arthropods; however, many aspects of their evolutionary relationships remain uncertain. We sequenced part of the mitochondrial cytochrome oxidase subunit I (COI) gene in 20 species of phytophagous mites belonging to nine genera and two families (Tetranychidae and Tenuipalpidae), including several agricultural pests. As reported in insects, the sequences were extremely rich in A+T (75% on average), especially in the third codon position (95%). However, one of the genera we studied had a significantly lower A+T content (69% on average, 78% in the third codon position), showing that base composition can change substantially over short periods of time. Most interspecific differences were transversions and their number increased steadily with the number of non-synonymous differences, while the number of transitions remained constant. The phylogeny based on COI sequences was inferred using the maximum likelihood method. The results are compatible as a whole with the traditional classification based on morphological characters, but call for some minor taxonomic revisions. Some morphological characters and life history traits (mode of reproduction, adaptation to the host plant) were also analysed within this phylogenetic framework. At the family level, one can see a trend towards thelytoky becoming rarer compared to the general mode of reproduction of the group, arrhenotoky. There is also an evolutionary tendency towards a more complex mode of life, with the production of silk webs and correlated changes of the locomotion apparatus. However, in the Tetranychidae there seems to have been convergent evolution of these morphological characters together with independent development of a common adaptation to this mode of life in different genera.