Evolution Of Mites Research Articles

Genetic diversification of an invasive honey bee ectoparasite across sympatric and allopatric host populations.

Invasive parasites are major threats to biodiversity. The honey bee ectoparasite, Varroa destructor, has shifted host and spread almost globally several decades ago. This pest is generally considered to be the main global threat to Western honey bees, Apis mellifera, although the damages it causes are not equivalent in all its new host's populations. Due to the high virulence of this parasite and the viruses it vectors, beekeepers generally rely on acaricide treatments to keep their colonies alive. However, some populations of A. mellifera can survive without anthropogenic mite control, through the expression of diverse resistance and tolerance traits. Such surviving colonies are currently found throughout the globe, with the biggest populations being found in Sub-Saharan Africa and Latin America. Recently, genetic differences between mite populations infesting surviving and treated A. mellifera colonies in Europe were found, suggesting that adaptations of honey bees drive mite evolution. Yet, the prevalence of such co-evolutionary adaptations in other invasive populations of V. destructor remain unknown. Using the previous data from Europe and novel genetic data from V. destructor populations in South America and Africa, we here investigated whether mites display signs of adaptations to different host populations of diverse origins and undergoing differing management. Our results show that, contrary to the differences previously documented in Europe, mites infesting treated and untreated honey bee populations in Africa and South America are genetically similar. However, strong levels of genetic differentiation were found when comparing mites across continents, suggesting ongoing allopatric speciation despite a recent spread from genetically homogenous lineages. This study provides novel insights into the co-evolution of V. destructor and A. mellifera, and confirms that these species are ideal to investigate coevolution in newly established host-parasite systems.

The mitogenome of Halotydeus destructor (Tucker) and its relationships with other trombidiform mites as inferred from nucleotide sequences and gene arrangements.

The redlegged earth mite, Halotydeus destructor (Tucker, 1925: Trombidiformes, Eupodoidea, Penthaleidae), is an invasive mite species. In Australia, this mite has become a pest of winter pastures and grain crops. We report the complete mitogenome for H. destructor, the first to represent the family Penthaleidae, superfamily Eupodoidea. The mitogenome of H. destructor is 14,691 bp in size, and has a GC content of 27.87%, 13 protein‐coding genes, two rRNA genes, and 22 tRNA genes. We explored evolutionary relationships of H. destructor with other members of the Trombidiformes using phylogenetic analyses of nucleotide sequences and the order of protein‐coding and rRNA genes. We found strong, consistent support for the superfamily Tydeoidea being the sister taxon to the superfamily Eupodoidea based on nucleotide sequences and gene arrangements. Moreover, the gene arrangements of Eupodoidea and Tydeoidea are not only identical to each other but also identical to that of the hypothesized arthropod ancestor, showing a high level of conservatism in the mitogenomic structure of these mite superfamilies. Our study illustrates the utility of gene arrangements for providing complementary information to nucleotide sequences with respect to inferring the evolutionary relationships of species within the order Trombidiformes. The mitogenome of H. destructor provides a valuable resource for further population genetic studies of this important agricultural pest. Given the co‐occurrence of closely related, morphologically similar Penthaleidae mites with H. destructor in the field, a complete mitogenome provides new opportunities to develop metabarcoding tools to study mite diversity in agro‐ecosystems. Moreover, the H. destructor mitogenome fills an important taxonomic gap that will facilitate further study of trombidiform mite evolution.

Varroa mite evolution: a neglected aspect of worldwide bee collapses?

While ectoparasitic Varroa mites cause minimal damage to their co-evolved ancestral host, the eastern honey bee (Apis cerana), they devastate their novel host, the western honey bee (Apis mellifera). Over several decades, the host switch caused worldwide population collapses, threatening global food security. Varroa management strategies have focused on breeding bees for tolerance. But, can Varroa overcome these counter-adaptations in a classic coevolutionary arms race? Despite increasing evidence for Varroa genetic diversity and evolvability, this eventuality has largely been neglected. We therefore suggest a more holistic paradigm for studying this host-parasite interaction, one in which 'Varroa-tolerant' bee traits should be viewed as a shared phenotype resulting from Varroa and honey bee interaction.

“More Than Meets the Eye”: Cryptic Diversity and Contrasting Patterns of Host-Specificity in Feather Mites Inhabiting Seabirds

Feather mites are useful models for studying speciation due to their high diversity and strong degree of host specialization. However, studies to date have focused on the evolution of higher-level mite taxa while much hidden diversity likely occurs at the level of host genera and species. In this study, we examined the diversity and evolution of feather mites infesting six sympatric seabird species from six genera, breeding in the Cape Verde archipelago. We report 32 feather mite morphospecies categorized into ten genera and three families, of which nine correspond to new, undescribed species. Molecular data corroborated morphological species descriptions, except for two morphologically-cryptic, but genetically distinct mite lineages related to Zachvatkinia oceanodromae and Laminalloptes simplex. Using these communities, we then applied a co-structure approach to test the contribution of ectosymbiont and host factors in driving feather mite evolution. Most seabird species hosted specific and unique feather mite species, even under sympatric conditions, and in general, feather mite species exhibited strong host-driven genetic structure. However, patterns of genetic differentiation were variable. That is, some mite species are more generalist than others and mite lineages/haplotypes can be shared by related seabird species. Interestingly, host-specific mites (eg., Zachvatkinia spp.) tend to display much higher intra-specific diversity compared to more generalist mites (eg., Microspalax and Plicatalloptes spp.). We discuss ectosymbiont and host life-history traits that might generate these patterns, such as host dispersal and breeding behavior and/or mite spatial and trophic specialization. Our findings highlight both the vast and largely unrecognized diversity of avian feather mites on seabirds, and the intrinsic complexity of the ecological processes underlying the evolution of these ectosymbionts.

Rewired RNAi-mediated genome surveillance in house dust mites.

House dust mites are common pests with an unusual evolutionary history, being descendants of a parasitic ancestor. Transition to parasitism is frequently accompanied by genome rearrangements, possibly to accommodate the genetic change needed to access new ecology. Transposable element (TE) activity is a source of genomic instability that can trigger large-scale genomic alterations. Eukaryotes have multiple transposon control mechanisms, one of which is RNA interference (RNAi). Investigation of the dust mite genome failed to identify a major RNAi pathway: the Piwi-associated RNA (piRNA) pathway, which has been replaced by a novel small-interfering RNA (siRNA)-like pathway. Co-opting of piRNA function by dust mite siRNAs is extensive, including establishment of TE control master loci that produce siRNAs. Interestingly, other members of the Acari have piRNAs indicating loss of this mechanism in dust mites is a recent event. Flux of RNAi-mediated control of TEs highlights the unusual arc of dust mite evolution.

Geography has a greater effect than Wolbachia infection on population genetic structure in the spider mite, Tetranychus pueraricola.

Wolbachia is an intracellular symbiotic bacterium that infects various spider mite species and is associated with alterations in host reproduction, which indicates the potential role in mite evolution. However, studies of Wolbachia infections in the spider mite Tetranychus pueraricola, a major agricultural pest, are limited. Here, we used multilocus sequence typing to determine Wolbachia infection status and examined the relationship between Wolbachia infection status and mitochondrial diversity in T. pueraricola from 12 populations in China. The prevalence of Wolbachia ranged from 2.8 to 50%, and three strains (wTpue1, wTpue2, and wTpue3) were identified. We also found double infections (wTpue1 + wTpue3) within the same individuals. Furthermore, the wTpue1 strain caused weak cytoplasmic incompatibility (CI) (egg hatchability ~55%), whereas another widespread strain, wTpue3, did not induce CI. There was no reduction in mitochondrial DNA (mtDNA) or nuclear DNA diversity among infected individuals, and mtDNA haplotypes did not correspond to specific Wolbachia strains. Phylogenetic analysis and analysis of molecular variance revealed that the distribution of mtDNA and nuclear DNA haplotypes were significantly associated with geography. These findings indicate that Wolbachia infection in T. pueraricola is complex, but T. pueraricola genetic differentiation likely resulted from substantial geographic isolation.

A Carboniferous Mite on an Insect Reveals the Antiquity of an Inconspicuous Interaction

Symbiosis [1], understood as prolonged interspecific association, is as ancient as the eukaryotic cell [2, 3]. A variety of such associations have been reported in the continental fossil record, albeit sporadically. As for mites, which as a group have been present since the Devonian (ca. 390 mya) [4,5] and are involved in a tremendous variety of modern-day symbioses, reported associations are limited to a few amber-preserved cases [6-11], with the earliest instance in the Cretaceous (ca. 85 mya) [11]. As a consequence, the antiquity and origin of associations involving small-sized mites and larger animals are poorly understood. Here we report, recovered from the Carboniferous Xiaheyan locality (ca. 320 mya), an oribatid mite located on the thorax of an extinct relative of grasshoppers, crickets, and katydids [12]. The mite was investigated using several methods, including phase-contrast tomography. The detailed morphological data allowed the placement of the mite in a new family within Mixonomata, whose fossil record is thus extended by ca. 250 Ma. Specimen and abundance distribution data derived from the fossil insect sample indicate that specimens from the corresponding excavation site were buried rapidly and were sub-autochthonous, indicating a syn vivo association. Moreover, the mite is located in a sequestered position on the insect. The observed interaction best fits the definition for phoresy, in which the benefit is transport and protection for the mite. This discovery demonstrates that this association, a trait shared by representatives of the most speciose mite taxa, arose very early during mite evolution.

Survey of mites in caves and deep soil and evolution of mites in these habitats

We studied adaptations to subterranean environments in Acari. Mite populations of two caves and of the mineral horizon of soil from three forest sites were analysed. In the soil, body length was limited by the pore size. The proportions of (i) predators, (ii) phoretic mites, and (iii) primitive oribatids were higher in caves. This was potentially explained by (i) polyphagy or predation on other groups and reduced interspecific competition, (ii) the fragmented structure and liability to flooding of the cave habitat, and (iii) the higher humidity in caves. Adaptations to dry habitats probably greatly influenced the evolution in Oribatida. It is proposed that numerous mites colonized caves directly from deep soil without a surface stage.

Book Review

MITES: ECOLOGY, EVOLUTION and BEHAVIOUR. By D. E. Walter & H. C. Proctor. CABI International, Wallingford, Oxon, U.K. 1999. Pp. 352. Hardcover. £42.50 (US$ 70.00). ISBN 085199 375 3. Acari (mites and ticks) form a major component of just about every terrestrial and aquatic habitat, and exhibit a myriad adaptations to fit them for a wide variety of life styles. The ease with which many species can be cultured, together with their short developmental time, make them ideal experimental animals. More often than not, however, acarines are excluded from behavioural, ecological and biodiversity studies. A fundamental obstacle to researchers wanting to obtain knowledge about these ubiquitous arthropods is the lack of suitable publications through which they can gain an entrée to the subject. The literature is widely scattered and there are few general accounts of the various aspects of acarine life. Comprehensive introductions to identification and functional morphology appear in Krantz 1978) and Evans 1992), respectively, and now Mites: Ecology, Evolution and Behaviour complements and, in a significant number of aspects, updates these two works. Walter & Proctor state that their reason for writing this book was the desire to attract new students to acarology by describing the interesting and exciting things that mites do. The evident and infectious enthusiasm of the authors for their subject, together with the wealth of examples they give, make it highly likely that this goal will be achieved. However, it is not just newcomers that will benefit from this book, because it is also a fine reference source for experienced acarologists wanting to locate information on subjects with which they are unfamiliar. The first chapter serves to introduce mites (the authors use the term to cover all acarines) and to outline the content of those that follow. A certain knowledge of mite evolution, morphology and systematics is necessary to appreciate the accounts of behaviours and relationships that form the bulk of this book, and chapters 2 and 3 contain detailed outlines which will appropriately equip readers. The remaining chapters include discussions of life cycles, development, dispersal strategies, the interrelationships between developmental rates and size, methods of sperm transfer, the impact of intrasexual competition and intersexual selection on morphology and behaviour, parthenogenesis, the many life styles and adaptations of free-living mites and those associated with plants and animals, biodiversity, and the role of mites as model organisms. A useful appendix lists journals, websites and courses dedicated to acarology, whereas the concluding detailed index enables data to be easily located. When presenting such an enormous amount of information, there is always the risk of overwhelming the reader, but the text of this book is thoughtfully subdivided and broken up by scanning electron micrographs and line drawings of impressive quality. Apart from the first, each chapter ends with a summary which allows the reader to digest the preceding information. The authors also include succinct additional information to aid the reader, e.g. the explanation given in chapter 1 of how phylogenies are constructed using cladistic methodology. Overall, the book is well produced and there are few typographical errors. Unfortunately, a number of papers cited in chapter 8 do not appear in the reference list; however, the authors have now made these available on the world-wide web (http://www.uq.edu.au/entomology/miteref.html). The sensitive pricing makes this book very good value and therefore not beyond the pocket of its intended audience. I am sure it will become a well thumbed reference for acarologists of all levels.

Water Mites: Phylogeny and Evolution.

Studies on water mite evolution regarding the phylogenetic implication are reviewed. Hydracarina is a large parasitengone mite group. Currently, more than 5, 000 species are integrated into 52 families in nine superfamilies. Although there are some conflicts on the origin of water mites, their monophyletic nature is suggested by several cladistic studies. The current taxonomic system of water mites does not reflect monophyletic groupings. Some researches have focused on phylogenetic relationships within Hydracarina, however, reliable hypotheses have not been obtained. Attempts to analyze data in a phylogenetic framework have been made in several ecological and behavioral studies. A comparative method has also been employed in a few studies, however, the real worth of this approach is not appreciated due to the absence of reliable phylogeny. Phylogenetic background estimated by modern cladistic methodology is indispensable for testing hypotheses on water mite evolution.

Assessment of lateral compression of the idiosoma in adult water mites as a taxonomic character and reclassification of Frontipodopsis Walter, Wettina Piersig and some other basal Hygrobatoidea (Acari : Hydrachnida)

Systematists have frequently interpreted lateral compression of the idiosoma in post-larval instars of water mites as a synapomorphy indicating common ancestry. This paper re-examines the evidence to support this assumption and concludes that lateral flattening has occurred independently several times during water mite evolution, and especially often in various basal clades of the superfamily Hygrobatoidea. Reassessment of the phylogenetic relationships of the genera attributed to these clades results in improved understanding of the early evolution and biogeography of hygrobatoid water mites and necessitates redefinition of several clades and significant revision of the family classification. The South African genus Karlvietsia K.O. Viets, 1962 is transferred from the subfamily Frontipodopsinae of the family Aturidae to the Hygrobatidae. The Australian genera Tasmanaxona Cook, 1986, Wheenyella Cook, 1986 and Wheenyoides Harvey, 1990 are also removed from Frontipodopsinae and placed with the genus Wettina Piersig, 1892, here removed from the family Pionidae, in the family Wettinidae Cook, stat. nov. Based on apparent relationship with members of Wettinidae, the South African genus Stormaxonella K.O. Viets, 1962 is transferred from the Aturidae and provisionally placed in the Wettinidae. The clade including the predominately Holarctic genus Lethaxona K.H. Viets, 1932 and the Western Hemisphere genus LethaxonellaCook, 1963 is recognised as the probable sister group of Wettinidae, and these genera are consequently removed from the Aturidae and placed in Lethaxonidae, fam. nov. The genus Frontipodopsis Walter is reassigned from Aturidae to the now monobasic family Frontipodopsidae K.H. Viets, stat. nov. Finally, five new species are described, including Frontipodopsis (Frontipodopsella) sudafricanus, sp. nov., Wettina occidentalis, sp. nov., Karlvietsia simplex, sp. nov., Hygrobates (Hygrobates) gereckei, sp. nov. and Hygrobates (Hygrobatides)frontipodoides, sp. nov., and both Karlvietsia brevipalpis K.O. Viets and K. angustipalpis K.O. Viets are redescribed.