Gerd Weigmann

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.

Radiation in sexual and parthenogenetic oribatid mites (Oribatida, Acari) as indicated by genetic divergence of closely related species

The D3 domain and its flanking regions of 28S rRNA of four pairs of closely related sexual species (Eupelops hirtus and E. torulosus; Oribatella calcarata and O. quadricornuta; Chamobates voigtsi and Ch. borealis; Liacarus coracinus and L. subterraneus) and four pairs of closely related parthenogenetic species (Nanhermannia nana and Na. coronata; Nothrus silvestris and No. palustris; Tectocepheus sarekensis and T. minor; Camisia spinifer and Ca. segnis) of oribatid mites were sequenced to investigate (1) if the D3 region can be used as a species marker and (2) if there is genetic variation among closely related species pairs and if its magnitude is related to reproductive mode. Furthermore, we investigated the world-wide genetic variation of the D3 region from the oribatid mite species Platynothrus peltifer. There was no intraspecific genetic variation in the D3 region in any of the species studied; it was even identical in two closely related parthenogenetic species (Na. nana and Na. coronata) and two closely related sexual species (E. hirtus and E. torulosus). The genetic differences of the other species pairs indicated that both parthenogenetic and sexual lineages have various ages. On average, however, the differences between the closely related parthenogenetic species were larger than those between closely related sexual species, indicating that parthenogenetic lineages exist historically and may radiate slower than sexual species. The findings of this study support the hypothesis that some of the parthenogenetic oribatid mite taxa (Tectocepheus, Nothrus) are ‘ancient asexuals’. The absence of intraspecific or intra-individual variation in the D3 region of parthenogenetic species is consistent with the presence of concerted evolution in the 28S rRNA gene. From this we infer the existence of a meiotic process, which is consistent with the automixy known from several other parthenogenetic oribatid species.

Integrative taxonomy: Combining morphological, molecular and chemical data for species delineation in the parthenogenetic Trhypochthonius tectorum complex (Acari, Oribatida, Trhypochthoniidae)

BackgroundThere is a long-standing controversial about how parthenogenetic species can be defined in absence of a generally accepted species concept for this reproductive mode. An integrative approach was suggested, combining molecular and morphological data to identify distinct monophyletic entities. Using this approach, speciation of parthenogenetic lineages was recently demonstrated for groups of bdelloid rotifers and oribatid mites. Trhypochthonius tectorum, an oribatid mite from the entirely parthenogenetic desmonomatan family Trhypochthoniidae, is traditionally treated as a single species in Central Europe. However, two new morphological lineages were recently proposed for some Austrian populations of T. tectorum, and were described as novel subspecies (T. silvestris europaeus) or form (T. japonicus forma occidentalis). We used the morphological and morphometrical data which led to this separation, and added mitochondrial and nuclear DNA sequences and the chemical composition of complex exocrine oil gland secretions to test this taxonomical hypothesis. This is the first attempt to combine these three types of data for integrative taxonomical investigations of oribatid mites.ResultsWe show that the previous European species T. tectorum represents a species complex consisting of three distinct lineages in Austria (T.tectorum, T. silvestris europaeus and T. japonicus forma occidentalis), each clearly separated by morphology, oil gland secretion profiles and mitochondrial cox1 sequences. This diversification happened in the last ten million years. In contrast to these results, no variation among the lineages was found in the nuclear 18S rDNA.ConclusionsOur approach combined morphological, molecular and chemical data to investigate diversity and species delineation in a parthenogenetic oribatid mite species complex. To date, hypotheses of a general oribatid mite phylogeny are manifold, and mostly based on single-method approaches. Probably, the integrative approach proposed here can be used to uncover further hidden biodiversity of glandulate Oribatida and help to build up more stable phylogenetic hypotheses in the future.

Morphology of adult and juvenile instars of Galumna obvia (Acari, Oribatida, Galumnidae), with discussion of its taxonomic status

Abstract The adult instar of the oribatid mite, Galumna obvia (Berlese, 1914), is redescribed in detail, on the basis of specimens from Finland. The morphology of juvenile instars of G. obvia is described and illustrated for the first time, and compared to that of other species of the family Galumnidae. The position of the insertion of the lamellar seta in adults proved variable in studied European populations, being either on or medial to the lamellar line. Since the genera Galumna and Pergalumna are currently distinguished only by the relative positions of the seta and line, specimens of G. obvia in some populations show an intermediate situation between other studied Galumna species – with lamellar seta on or lateral of lamellar line – and Pergalumna with lamellar seta at a distinct distance medially of lamellar line. A detailed reevaluation of the two genera is needed.

Acari: Limnic Oribatida

In Europe (excluding Caucasus and Macaronesian Islands) SCHATZ (2005) calculates in total about 2100 species of described oribatid mite species, worldwide about 10.000 species. In Germany about 520 species are determined and evaluated (without several synonyms; after WEIGMANN 2006). The considered geographical region of this chapter is Central Europe, i. e. Germany and the surrounding countries; other Eastern European countries are excluded, as well as the mediterranean region, if not mentioned especially.

Anomalies of notogastral structures in poronotic oribatid mites (Oribatida: Poronota) interpreted as cryptic ancestral characters modulated by regulatory genes

Occasionally, specimens of oribatid mites have abnormal asymmetric characters, e.g., regarding notogastral setation or the porose areas of the octotaxic system, similar to those in other more or less related taxa, or similar to those in ancestors. Exemplarily, anomalies in specimens of Scheloribatidae and Phenopelopidae are presented. A model is proposed involving chains of regulatory genes that explains evolutionary changes within branches of poronotic Oribatida as well as the notogastral anomalies discussed. This model may contribute towards a revised strategy for taxonomy and phylogenetical systematics.

Morphological variability in populations of a thelytokous mite, Trhypochthoniellus longisetus (Oribatida), with notes on synonymy

Two well-known morphs of Trhypochthoniellus in Europe, the first with developed bothridia and sensilli in adults (‘T. trichosus (Schweizer, 1922)’), and the second without (‘T. setosus Willmann, 1928’) are regarded as junior synonyms of the polymorphic and thelytokous species Trhypochthoniellus longisetus (Berlese, 1904). Three populations have been studied morphometrically. In one population all degrees of trichobothridial regression have been found, many of the specimens being asymmetrical. The species is considered to include morphologically different clones.

New Carabodidae (Acari: Oribatida) of Georgia

The Carabodidae is a large and globally distributed family of oribatid mites with about 34 genera (Mahunka 1986, 1987) and many species. Three genera of Carabodidae have been recorded from Georgia: Austrocarabodes Hammer, 1966, Carabodes C. L. Koch, 1835 and Odontocepheus Berlese, 1913, with 17 species in total (see Shtanchaeva 2001). Research carried out recently in different regions of Georgia provided additional knowledge on the taxonomy and distribution of these mites (Weigmann & Murvanidze 2003). In this paper we describe a new species (Carabodes djaparidzae sp. n.) and a new subspecies (Austrocarabodes foliaceisetus georgiensis subsp. n.) and additionally, a regional form of the Nearctic Carabodes granulatus Banks, 1895. This paper contributes to a revision of the regional fauna of Georgia, a region which links three Palaearctic biogeographical regions (Caucasian region, partly alpine – Turkish and Iranian regions, subtropic to tropic) and, therefore, is of high biogeographical interest. This revision includes critical discussion of earlier descriptions of Caucasian species and of Georgian records of species described from other regions originally. Material and methods The material was collected by soil samples; the mites were extracted by use of modified Berlese-funnels. The animals were stored in ethanol until preparation and were studied after clearance in lactic acid in open hollow-ground microscope slides covered partly with a cover slip, which allows to view the animal in different positions. Permanent slide preparations are mounted in modified Berlese-fluid. The terminology of morphological structures follows van der Hammen (1980) and Weigmann (2006).

Morphological variability between and within populations of Tectocepheus (Acari, Oribatida, Tectocepheidae) from the velatus-complex in Central Europe

The morphologically different forms of the Tectocepheus velatus complex are regarded by some authors to he a group of closely related species, in Europe, for instance, including T velatus s. str., T. sarekensis, T tennis, 2: knuellei and T alatus. Other authors summarize all these species under ‘T velatus (s. 1.)’. This opinion seems to be supported by the continuous expression of some morphological characters, such as body length, within a great range of variability.

A new species of Trhypochthoniellus (Acari: Oribatida: Trhypochthoniidae) from Chile, with remarks on diagnosis of the genus

Abstract A new species of oribatid mite of the genus Trhypochthoniellus (Oribatida: Trhypochthoniidae) is described from mosses in a swamp of vicinity of Punta Arenas, Chile. Trhypochthoniellus chilensis sp. n. differs from all species of the genus by the presence of monodactylous legs and notogastral setae p3, clearly greater distance between c1-c1 than d1-d1 and three pairs of setae on epimeres IV. Comparative morphological analysis of the species and a revised diagnosis of the genus are presented.