Roy A. Norton

Morphological evidence for the evolutionary origin of Astigmata (Acari: Acariformes)

A century ago, Antonio Berlese first discussed the close phylogenetic relationship between the large mite groups Oribatida and Astigmata. Since then, information having phylogenetic value has greatly increased and the paradigms within which we interpret it have changed. Herein I refine the general hypothesis that Astigmata originated within oribatid mites and suggest Malaconothridae as a possible sister group. Among the 14 apomorphies used to support the origin of Astigmata within oribatid mites are possession of lateral opisthosomal glands, regression of hysterosomal setal pair f1, paired prelarval denticles, partially internalized chelicerae with incomplete adaxial walls, an atelobasic rutellum, pretarsal condylophores that articulate posteriorly with the tarsus, a dorsally fused palp tibia and tarsus and transdehiscent ecdysis. A further 13 apomorphies support the origin of Astigmata at some level within Malaconothroidea. These include absence of an oblique labiogenal articulation, presence of a distal rutellar lamella, shortening of the palp tarsus, larval regression of hysterosomal seta f2, loss of the bothridial seta in all instars, and several losses and modifications of leg setae. The hypothesis brings to light evolutionary questions that were previously obscured by incorrect or inappropriate classifications. The nomenclatural problems that arise from it are best solved by considering Astigmata as a subgroup within Oribatida.

Early land animals in north america: evidence from devonian age arthropods from gilboa, new york.

A new fossil site near Gilboa, New York, is one of only three where fossils of terrestrial arthropods of Devonian age have been found. The new Gilboan fauna is younger than the other two but richer in taxa. Fragmentary remains and nearly whole specimens assigned to Eurypterida, Arachnida (Trigonotarbida, Araneae, Amblypygi, and Acari), Chilopoda [Craterostigmatomorpha(?) and Scuterigeromorpha(?)], and tentatively to Insecta (Archaeognatha) have been found. The centipedes and possible insects may represent the earliest records known for these groups.

Oribatid mites and the decomposition of plant tissues in Paleozoic coal-swamp forests

Although oribatid mites are essential to the decomposition of plant tissues in modern temperate forests by assisting conversion of primary productivity to soil organic matter, little is known of their paleoecologic history. Previously there has been scattered and anecdotal evidence documenting oribatid mite detritivory in Pennsylvanian plant tissues. This study evaluates the incidence of oribatid mite damage for seven major coal-ball deposits from the Illinois and Appalachian sedimentary basins, representing a 17 million year interval from the Euramerican tropics. Although this interval contains the best anatomically preserved plant tissues with oribatid mite borings in the fossil record, coeval oribatid mite body-fossils are absent. By contrast, the known body-fossil record of oribatid mites commences during the Middle Devonian, but does not reappear until the Early Jurassic, at which time mite taxa are modern in aspect. All major plant taxa occurring in Pennsylvanian coal swamps, including lycopsids, sphenopsids, ferns, seed ferns and cordaites, were consumed by oribatid mites. Virtually every type of plant tissue was used by mites, notably indurated tissues such as bark, fibrovascular bundles and especially wood, as well as softer seed megagametophytic and parenchymatic tissues within stems, roots and leaves. Significant evidence also exists for secondary consumption by mites of tissues in macroarthropod coprolites. Our data indicate that oribatid mites consumed dead, aerially-derived plant tissues at ground level, as well as root-penetrated tissues substantially within the peat. Oribatid mites were important arthropod decomposers in Pennsylvanian coal swamps of Euramerica. The wood boring functional-feeding-guild was expanded by insects into above-ground, live trees during the early Mesozoic. New food resources for insect borers resulted from penetration of live tissues such as cambium and phloem, and the invasion of heartwood and other hard tissues mediated by insect-fungus symbioses. Termites and holometabolous insects were prominent contributors to this second wave of wood-boring, exploiting gymnosperms and angiosperms as both detritivores and herbivores. An earlier emplacement of oribatid mites as detritivores of dead plant tissues continued to the present, but without a documented trace-fossil record.

Oribatid mites as a major dietary source for alkaloids in poison frogs

Alkaloids in the skin glands of poison frogs serve as a chemical defense against predation, and almost all of these alkaloids appear to be sequestered from dietary arthropods. Certain alkaloid-containing ants have been considered the primary dietary source, but dietary sources for the majority of alkaloids remain unknown. Herein we report the presence of ≈80 alkaloids from extracts of oribatid mites collected throughout Costa Rica and Panama, which represent 11 of the ≈24 structural classes of alkaloids known in poison frogs. Forty-one of these alkaloids also occur in the dendrobatid poison frog, Oophaga pumilio, which co-occurs with the collected mites. These shared alkaloids include twenty-five 5,8-disubstituted or 5,6,8-trisubstituted indolizidines; one 1,4-disubstituted quinolizidine; three pumiliotoxins; and one homopumiliotoxin. All but the last of these alkaloid classes occur widely in poison frogs. In addition, nearly 40 alkaloids of unknown structure were detected in mites; none of these alkaloids have been identified in frog extracts. Two of these alkaloids are homopumiliotoxins, five appear to be izidines, four appear to be tricyclics, and six are related in structure to poison frog alkaloids that are currently unclassified as to structure. Mites are common in the diet of O. pumilio, as well as in the diets of other poison frogs. The results of this study indicate that mites are a significant arthropod repository of a variety of alkaloids and represent a major dietary source of alkaloids in poison frogs.

The distribution, mechanisms and evolutionary significance of parthenogenesis in oribatid mites

Highly derived oribatid mites (Brachypylina) seem to fit most predictions of evolutionary theory regarding the ecological, geographical and taxonomic distribution of parthenogenesis. Earlier derivative groups generally do not. We suggest that the ancestors of large, completely parthenogenetic families (for example, Brachychthoniidae, Lohmanniidae, Camisiidae, Trhypoch-thoniidae, Malaconothridae, Nanhermanniidae) were themselves parthenogenetic, and that’ speciation’ and radiation occurred in the absence of sexual reproduction. Further, it is speculated that automixy (meiotic thelytoky) was the process involved — even though some extant species may prove to be secondarily apomictic, just as apomicts evolve from sexually reproducing lineages. If mechanisms for maintaining heterozygosity are effective, automixy can provide all the advantages of parthenogenesis, plus the DNA-repair advantage of meiosis. Genotypes can be diversified by the formation of distinct clones, thereby providing the raw material for successful radiation. The disadvantage of such a system would be its slow rate of change due to the absence of an allele-recruitment mechanism. Much of the above remains speculative since available data are meagre. Future work should include surveys of thelytokous mechanisms in oribatid mites, the genetic characterization of populations of a variety of parthenogenetic and sexual species, and the refinement of hypotheses on phylogenetic relationships of parthenogenetic taxa.

High genetic divergences indicate ancient separation of parthenogenetic lineages of the oribatid mite Platynothrus peltifer (Acari, Oribatida)

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.

Reevolution of sexuality breaks Dollo's law.

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 Dollos 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.

Molecular phylogeny of oribatid mites (Oribatida, Acari): evidence for multiple radiations of parthenogenetic lineages

Nucleotide sequences of the D3 expansion segment and its flanking regions of the 28S rDNA gene were used to evaluate phylogenetic relationships among representative sexual and asexual oribatid mites (Oribatida, Acariformes). The aim of this study was to investigate the hypothesis that oribatid mites consist of species rich clusters of asexual species that may have radiated while being parthenogenetic. Furthermore, the systematic position of the astigmate mites (Astigmata, Acariformes) which have been hypothesised to represent a paedomorphic lineage within the oribatid mites, is investigated. This is the first phylogenetic tree for oribatid mites s.1. (incl. Astigmata) based on nucleotide sequences. Intraspecific genetic variation in the D3 region was very low, confirming the hypothesis that this region is a good species marker. Results from neighbour joining (NJ) and maximum parsimony (MP) algorithms indicate that several species rich parthenogenetic groups like Camisiidae, Nanhermanniidae and Malaconothridae are monophyletic, consistent with the hypothesis that some oribatid mite groups diversified despite being parthenogenetic. The MP and maximum likelihood (ML) method indicated that the D3 region is a good tool for elucidating the relationship of oribatid mite species on a small scale (genera, families) but is not reliable for large scale taxonomy because branches from the NJ algorithm collapsed in the MP and ML tree. In all trees calculated by different algorithms the Astigmata clustered within the oribatid mites, as proposed earlier.

Observations on phoresy by oribatid mites (Acari: Oribatei)

Abstract Phoretic oribatid mites are recorded from specimens of 31 insect species, mostly passalid beetles. Mites were predominantly of the families Mesoplophoridae, Oppiidae and Oribatulidae. The former attaches by grasping a hair between the aspis and genital plate. A degree of attachment site specificity, but not host-species specificity, is exhibited by certain mites.

Cytogenetics of Holokinetic Chromosomes and Inverted Meiosis: Keys to the Evolutionary Success of Mites, with Generalizations on Eukaryotes

The evolution of sexual reproduction has seen a recent and major resurgence as a topic of interest. Many authors (e.g. Ghiselin 1974, Williams 1975, Maynard Smith 1978, Bell 1982, Shields 1982, Bull 1983, Michod and Levin 1988) have refined the now-familiar arguments that generally cast sexual reproduction as the alternative to the asexual production of genetic clones. As theorists have moved further from the usual cytogenetic models (i.e. humans, mice, fruitflies and maize), we have learned that the many strange genetic systems and breeding biologies of plants, animals and protists blur the distinction between “sexual” and “asexual”.