The Taxonomy, Phylogenetics And Evolution Of Eriophyoid Mites Base On Morphology And Molecular Markers (Acari:Eriophyoidea)

Eriophyoid mites (Acari:Eriophyoidea) are worldwide distributed and phytophagous. They are exceptionally diverse and up to 4000 species are reported. They are highly host-specific with nearly 80% of the species reported from only one host plant. They are small and have the unique body structure compared to other groups of Acari. They are second only to spider mites in their economic importance. Some eriophyoid mites are agricultural pests while some are potential bio-control agents of weeds. As a result, there is a growing demand for their accurate and rapid taxonomies. They often show a host-associated evolutionary pattern, which is considered as an important evidence of natural selection.Previously, the taxonomy of this group was based on morphology only. However, phylogenetic relationships in this group could be incorrect if the diagnostic morphological characters are homoplastic. Therefore, the phylogeny of 112 representative taxa from Eriophyoidea was determined using three fragments of rRNA. Phylogenetic relationships were inferred through Bayesian, maximum likelihood and maximum parsimony methods, and then a number of clades or major clades were defined according to robust phylogenetic topologies combined with morphological comparison. Tests of monophyly showed that two of three families of Eriophyoidea as well as one subfamily and four tribes were not monophyletic. Ancestral character state reconstruction (ACSR) showed that five diagnostic morphological characters evolved several times, confounding the current taxonomy. Additionally, reconstruction of the history of host plant colonization suggested host switching occurred in a limited range of host plants. The host association data made it possible to determine taxonomic relationships more accurately. These results show that by integrating morphological and molecular information and host plant choice, it is possible to obtain a more accurate taxonomy and deeper phylogenetic understanding of Eriophyoidea.Eriophyoid mites are greatly different from other members of Acari or Acariformes in morphology. Up to now, there is no reasonable explaination for this punctuated evolution. Moreover, the discovery of the Triassic fossils of eriophyoid mites suggests a more ancient history than we previously thought. Previously, we have detected the host-assocatied pattern in macroevolution of eriophyoid mites. So it is expected that the evolution of the mites is promoted by the evolution of their hosts. To figure out such scientific issues, we reconstructed the phylogenetic relationships among represented eriophyoid mite species and their Acari outgroups based on the whole 18S rRNA. We also calculated the divergence time based on the obtained tree topology and several fossil calibrations. The results of this research supported the Eriophyoidea belongs to Acariformes, but the relationships between Eriophyoidea and other members of Trombidiformes is still unclear. According to the comparison of histories of eriophyoid mites and their host plants, it was reasonable that the Devounian origin of gymnosperm and the Cretaceous explosion of angiosperm and mass Cretaceous-Paleogene extinction influenced the evolution of eriophyoid mites. "Diversity drives diversity", which means the diversity of host plants drives the diversity of mites. However, it should be noticed that the lack of more outgroups and endemic eriophyoid mite species may influence our results. Much more taxa and homologous evidences are are expected.Eriophyoid mites are worldwide distributed. They almost can be found whereever the plants exist. Because of the close relationship between these mites and their host plants, the vegetation of each region should be seriously considered in the analysis of fauna of these mites. According to the results of molecular phylogenetics, the distributions of four groups of eriophyoid mites in six regions were summarized. Our results explored the relationships between mites and plants in their varieties and abundances. We also recognized that the other ecological factors or geographic isolations influenced their distributions. However, the present insufficiency and region-imbalance of survays of eriophyoid mites limited our understanding of their fauna.The technology of molecular markers has an advantage in detect the cryptic speciation of eriophyoid mites, which is usually host-associated. However, the implications of such cryptic diversity appear to differ when methods based on different types of data are used. Here, samples of a host-associated eriophyoid mite species, Tetra pinnatifidae, collected from different host plants and localities are evaluated. The congruence of results based on morphometric (32 characters), mitochondrial (16S), and nuclear (28S) data was evaluated and showed a host-associated cryptic diversity dividing this morphospecies into several groups/clades that were morphometrically indistinguishable. In comparison, the 16S data confirmed cryptic speciation and intra-clade host-associated diversity while 28S did not. In contrast,28 S data revealed potential gene flow between host-associated populations. High mitochondrial divergence, as well as low nuclear and morphological divergence indicated very recent stage of cryptic diversity of this eriophyoid mite.Host plants usually play a crucial role in the first step of speciation, leading to host-associated differentiation (HAD) among populations that use different host plants. Previous studies of eriophyoid mite species have revealed HAD using morphometric and molecular methods. In the present study, we tested the hypothesis that HAD occurred among different populations of the pink tea mite, Acaphylla theae and the purple tea mite, Calacarus carinatus from three tea-producing areas of China. These tea-producing areas grow recently radiated varieties of tea. Therefore, diversification within these phytophagous mites was expected. However, using a K2P comparison, network analyses pairwise FST and AMOVA based on mitochondrial and nuclear markers, no association between genetic diversity and host plant species was detected. Moreover, a very low level of haplotype and nucleotide diversity and a lack of geographical structure were found. The absence of genetic differentiation among host-associated populations suggests that these two species are real generalists of different varieties of tea. The limited genetic diversity among the populations of these two species can be attributed to their recent colonization of tea, and to their passive spread by frequent human commercial activities.Natural selection plays a crucial role in the primate action of divergenc or speciation. Such evidence can be found from HAD of morpho-species of eriophyoid mites. Different host plants exert different selection pressure to their mites, and thus promote their independent evolution. Up to now, several researches of eriophyoid mites showed HAD among host-associated populations. However, our understanding of HAD of eriophyoid mites may be misled when the absemce of HAD is detected, or the divergence involves in geographic isolation, or the selected taxa are limited. In this research, we expected to explore the regular pattern of HAD of eriophyoid mites through the survey of gymnosperm-eriophyoid community in Oriental realm of China. The population genetic structures of fourteen morpho-species in this community were analyzed based on on two molecular markers. Although these populations of different morpho-species were in the similar host plants or environmental conditions, the HAD of them was not a common phenomenon. Most of the geographic populations had ongoing gene flow, though they may involve in geographic isolation. Their communication can be explained by frequent passive dispersal. The analyzed morpho-species showed different population structures, which were arttibuted to their difference of host choices and histories of host evolution. Eriophyoid mites are under stabilizing selection when they are in conserved host environment. In constract, when their hosts evolve rapidly, their selection pressures as well as evolutionary patterns are various.