The dominance of sexual reproduction is still an unresolved enigma in evolutionary biology. Strong advantages of sex have to exist, because only a few parthenogenetic taxa persist over evolutionary timescales. Oribatid mites (Acari) include outstanding exceptions to the rule that parthenogenetically reproducing taxa are of recent origin and doomed to extinction. In addition to the existence of large parthenogenetic clusters in oribatid mites, phylogenetic analyses of this study and model-based reconstruction of ancestral states of reproduction imply that Crotoniidae have reevolved sexuality from parthenogenetic ancestors within one of those clusters. This reversal in reproductive mode is unique in the animal kingdom and violates Dollo's law that complex ancestral states can never be reacquired. The reevolution of sexuality requires that ancestral genes for male production are maintained over evolutionary time. This maintenance likely is true for oribatid mites because spanandric males exist in various species, although mechanisms that enable the storage of genetically ancestral traits are unclear. Our findings present oribatid mites as a unique model system to explore the evolutionary significance of parthenogenetic and sexual reproduction.oribatid mites ͉ parthenogenesis ͉ spanandric males ͉ automixis ͉ ancient asexuals

Theories on the evolution and maintenance of sex are challenged by the existence of ancient parthenogenetic lineages such as bdelloid rotifers and darwinulid ostracods. It has been proposed that several parthenogenetic and speciose taxa of oribatid mites (Acari) also have an ancient origin. We used nucleotide sequences of the mitochondrial gene cytochrome oxidase I to estimate the age of the parthenogenetic oribatid mite species Platynothrus peltifer. Sixty‐five specimens from 16 sites in North America, Europe and Asia were analysed. Seven major clades were identified. Within‐clade genetic distances were below 2 % similar to the total intraspecific genetic diversity of most organisms. However, distances between clades averaged 56 % with a maximum of 125 %. We conclude that P. peltifer, as it is currently conceived, has existed for perhaps 100 million years, has an extant distribution that results from continental drift rather than dispersal and was subject to several cryptic speciations.

Background: Complete mitochondrial (mt) genomes and the gene rearrangements therein are increasingly used as molecular markers for investigating phylogenetic relationships, especially for elucidating deep splits. Contributing to the complete mt genomes of arthropods, especially Arachnida, available so far, we provide the first complete mt genome of a sarcoptiform mite species, the sexually reproducing oribatid mite Steganacarus magnus (Acari, Oribatida) which was determined by sequencing of long PCR products.

It has been hypothesized that in ancient apomictic, nonrecombining lineages the two alleles of a single copy gene will become highly divergent as a result of the independent accumulation of mutations (Meselson effect). We used a partial sequence of the elongation factor‐1α (ef‐1α) and the heat shock protein 82 (hsp82) genes to test this hypothesis for putative ancient parthenogenetic oribatid mite lineages. In addition, we tested if the hsp82 gene is fully transcribed by sequencing the cDNA and we also tested if there is evidence for recombination and gene conversion in sexual and parthenogenetic oribatid mite species. The average maximum intra‐specific divergence in the ef‐1α was 2.7% in three parthenogenetic species and 8.6% in three sexual species; the average maximum intra‐individual genetic divergence was 0.9% in the parthenogenetic and 6.0% in the sexual species. In the hsp82 gene the average maximum intra‐individual genetic divergence in the sexual species Steganacarus magnus and in the parthenogenetic species Platynothrus peltifer was 1.1% and 1.2%, respectively. None of the differences were statistically significant. The cDNA data indicated that the hsp82 sequence is transcribed and intron‐free. Likelihood permutation tests indicate that ef‐1α has undergone recombination in all three studied sexual species and gene conversion in two of the sexual species, but neither process has occurred in any of the parthenogenetic species. No evidence for recombination or gene conversion was found for sexual or parthenogenetic oribatid mite species in the hsp 82 gene. There appears to be no Meselson effect in parthenogenetic oribatid mite species. Presumably, their low genetic divergence is due to automixis, other homogenizing mechanisms or strong selection to keep both the ef‐1α and the hsp82 gene functioning.

Astigmata comprise a diverse group of acariform mite species with a remarkable range of life histories, most of which involve parasitic or commensal relationships with other organisms. Several authors have suggested that Astigmata evolved as a paedomorphic clade from within Oribatida, and both morphology and gland-chemistry strongly suggest that their sister-clade is within the oribatid subgroup Desmonomata. The biologies of these groups contrast greatly, since oribatid mites are mostly soil-living detritivores and fungivores, and have life cycles that are much longer than those in Astigmata. We tested the hypothesis that Astigmata evolved from within Desmonomata using two molecular markers, the ribosomal 18S region (18S) and the nuclear elongation factor 1 alpha (ef1alpha) gene. Representative acariform mites included 28 species of Oribatida, eight of Astigmata, two of Prostigmata and two of Endeostigmata; outgroups included members of Opilioacariformes, Parasitiformes and Ricinulei. To minimize the possibility of long-branch attraction artifacts, we limited highly variable sites by removing gaps (18S) and third codon positions (ef1alpha) from the sequences. Maximum parsimony, neighbor-joining and Bayesian algorithms formed trees that consistently placed Astigmata outside monophyletic Oribatida, usually as sister-group of the endeostigmatid mite Alicorhagia sp. Analyses with and without outgroups resulted in similar topologies, showing no evidence for long-branch artifacts and leaving the conflict with morphological and biochemical data unexplained.