Chrysomelidial in the Opisthonotal Glands of the Oribatid Mite, Oribotritia berlesei

Gas chromatographic–mass spectrometric analyses of whole body extracts of Oribotritia berlesei, a large-sized soil-dwelling oribatid mite, revealed a consistent chemical pattern of ten components, probably originating from the well-developed opisthonotal glands. The three major components of the extract were the iridoid monoterpene, (3S,8S)-chrysomelidial (about 45% of the extract), the unsaturated hydrocarbon 6,9-heptadecadiene, and the diterpene β-springene (the latter two, each about 20–25% of the extract). The remaining minor components (together about 10% of the extract) included a series of hydrocarbons (tridecene, tridecane, pentadecene, pentadecane, 8-heptadecene, and heptadecane) and the tentatively identified 9,17-octadecadienal. In contrast, analysis of juveniles showed only two compounds, namely a 2:1 mixture of (3S,8S)-chrysomelidial and its epimer, epi-chrysomelidial (3S,8R-chrysomelidial). Unexpectedly, neither adult nor juvenile secretions contained the so-called astigmatid compounds, which are considered characteristic of secretions of oribatids above moderately derived Mixonomata. The chrysomelidials, as well as β-springene and octadecadienal, are newly identified compounds in the opisthonotal glands of oribatid mites and have chemotaxonomic potential for this group. This is the first instance of finding chrysomelidials outside the Coleoptera

Gonads and gametogenesis in astigmatic mites (Acariformes: Astigmata)

AbstractAstigmatans are a large group of mites living in nearly every environment and exhibiting very diverse reproductive strategies. In spite of an uniform anatomical organization of their reproductive systems, gametogenesis in each sex is highly variable, leading to gamete formation showing many peculiar features and emphasizing the distinct position of Astigmata. This review summarizes the contemporary knowledge on the structure of ovaries and testes in astigmatic mites, the peculiarities of oogenesis and spermatogenesis, as well as provides new data on several species not studied previously. New questions are discussed and approaches for future studies are proposed

DNA metabarcoding reveals modern and past eukaryotic communities in a high-mountain peat bog system

Peat bogs located in high mountains are suitable places to study local environmental responses to climate variability. These ecosystems host a large number of eukaryotes with diverse taxonomic and functional diversity. We carried out a metabarcoding study using universal 18S and COI markers to explore the composition of past and present eukaryotic communities of a Pyrenean peat bog ecosystem. We assessed the molecular biodiversity of four different moss micro-habitats along a flood gradient in the lentic Bassa Nera system (Central Pyrenees). Five samples collected from different sediment depths at the same study site were also analysed, to test the suitability of these universal markers for studying paleoecological communities recovered from ancient DNA and to compare the detected DNA sequences to those obtained from the modern community. We also compared the information provided by the sedimentary DNA to the reconstruction from environmental proxies such as pollen and macro-remains from the same record. We successfully amplified ancient DNA with both universal markers from all sediment samples, including the deepest one (~ 10,000 years old). Most of the metabarcoding reads obtained from sediment samples, however, were assigned to living edaphic organisms and only a small fraction of those reads was considered to be derived from paleoecological communities. Inferences from ancient sedimentary DNA were complementary to the reconstruction based on pollen and macro-remains, and the combined records reveal more detailed information. This molecular study yielded promising findings regarding the diversity of modern eukaryotic peat bog communities. Nevertheless, even though information about past communities could be retrieved from sediment samples, preferential amplification of DNA from living communities is a caveat for the use of universal metabarcoding markers in paleoecology

Development and function of the genital organs in the parthenogenetic oribatid mite Archegozetes longisetosus Aoki 1965

Archegozetes longisetosus Aoki 1965 is a parthenogenetic oribatid mite, that has a pantropical-disjunct distribution. It is a member of the family of Trhypochthoniidae. Its ease of rearing, rapid succession of generations and high fecundity fulfill central requirements of a suitable model organism. Roy A. Norton in 1993 founded a laboratory strain from a single puertorican female, Archegozetes longisetosus ran, which is since kept in laboratories worldwide. This laboratory strain lead to A. longisetosus being the most thoroughly studied oribatid mite. The species is of special interest in studies on evolutionary biology, as it is a member of a cluster of obligatory parthenogenetic species, for which molecular studies have indicated a very old age of probably more than a hundred million years. Detailed insight in the reproduction of A. longisetosus therefore does not only broaden our knowledge of a model organism, but may also contribute to a better understanding of the ancillary conditions of uni- vs. bisexual propagation, as well as the differential likelihood of long term stability in different forms of unisexual propagation. One step on the way towards this goal, and a necessary condition for future studies, is the acquisition of anatomical data regarding structure, function and development of organs and tissues. This cognitive interest lay at the starting point of the study at hand. With the aid of high-resolution synchrotron X-ray micro computer tomographies (SR-μCT), three-dimensional models of the genital organs and their precursors were obtained from all freeliving instars (larva to adult). As several models per instar at intervals of several days were obtained, important insight in developmental processes was gained. Already in the larva, germinative and somatic portions of the genital anlage can be distinguished. Further development proceeds continously, and largely independent from cuticular moulting. Precursors of the oviducts start to develop in the protonymphal stage, whereas proliferation of the germcells takes place during the deutonymphal stage. Ectodermal portions of the genital systems start development in the tritonymphal stage. The oviducts apparently do not form as evaginations of a coelomic sac containing germline cells, but either as lateral folds of the coelomic cavity or as lateral evaginations, which retrogradally form secondary contact sites to the germinative portion. Further investigations are needed to establish the mode of oviduct formation unequivocally. Three-dimensional models also facilitated the planning of semi- and ultrathin serial sectionings, which yielded histological and functional information. Observations made using electron- and lightmicroscopy included the onset of meiosis I in the tritonymphal stage, uptake of yolk precursors from the fat body into the oocyte via microvilli and coated pits, accumulation of egg shell material simultaneous to yolk accumulation, and the solidification of the egg shell upon passing into the oviduct. These observations justified a nomenclature of the genital system and the classification of the ovary as panoistic. Additionally, the oviducts could be described as a sheltered space for embryonal development. In summary, the results indicate that the loss of fertilization in the reproduction of A. longisetosus permits both anatomical and temporal compaction of the related processes, enabling relatively high average reproductive rate, even in the face of short-term unstable environmental conditions. The selection of methods permitted to demonstrate the mechanism of thelytoky by terminal fusion automixis with inverted (postreductional) meiosis in a functional context, and to present A. longisetosus as a promising model system also for questions beyond the borders of the taxon chelicerata.Archegozetes longisetosus Aoki 1965 ist eine parthenogenetische Hornmilbe mit pantropisch-disjunkter Verbreitung aus der Familie der Trhypochthoniidae. Durch ihre einfache Haltung, schnelle Generationenfolge und hohe Fruchtbarkeit erfüllt sie wesentliche Merkmale eines geeigneten Modellorganismus. 1993 wurde von Roy A. Norton aus einem einzelnen puertoricanischen Weibchen ein Laborstamm etabliert, A. longisetosus ran, der inzwischen weltweit in Laboren vertreten ist, was mit dazu führte, dass A. longisetosus mittlerweile die insgesamt am besten untersuchte Hornmilbe darstellt. Von besonderem Interesse ist die Art für evolutionsbiologische Studien, Da sie zu einem Schwarm obligat parthenogenetischer Linien gehört, für die molekulare Studien ein sehr hohes Alter von evtl. über hundert Millionen Jahren nahelegen. Ein genaues Verständnis der Fortpflanzungsvorgänge von A. longisetosus dient also nicht nur der Erweiterung unserer allgemeinen Kenntnis eines Modellorganismus, sondern darüber hinaus dem besseren Verständnis der Randbedingungen ein- und zweigeschlechtlicher Fortpflanzung, sowie der unterschiedlich langen Überlebenswahrscheinlichkeit der verschiedenen Formen eingeschlechtlicher Fortpflanzung. Ein Schritt auf dem Weg zu diesem Verständnis, und notwendige Bedingung für weiterführende Studien, ist der Aufbau einer anatomischen Datengrundlage zu Aufbau, Funktion und Entwicklung der an der Fortpflanzung beteiligten Organe und Gewebe. Dieses Erkenntnisinteresse lag der vorliegenden Arbeit zugrunde. Anhand hochauflösender Synchrotron- Röntgen- Mikro- Computer- Tomographien (SR-μCT) wurden dreidimensionale Modelle der Genitalorgane und ihrer Anlagen in allen freilebenden Stadien von der Larve bis zum Adultus erstellt. Da pro Entwicklungsstadium mehrere Modelle im Abstand weniger Tage erstellt werden konnten, konnten so wichtige Erkenntnisse über die Entwicklung der Genitalorgane gewonnen werden. So zeigte sich, dass schon in Larvenstadien ein somatischer und ein germinativer Anteil der Genitalanlage unterschieden werden kann. Die weitere Entwicklung dieser Anlage verläuft kontinuierlich, und weitgehend unabhängig von den Häutungen der Körperhülle. Vorläufer der Ovidukte beginnen sich ab der Protonymphe zu entwickeln, während die Vermehrung der Eizellen in der Deutonymphe stattfindet. Ab der Tritonymphe bilden sich auch die ektodermalen Anteile des Genitalsystems aus. Die Ovidukte bilden sich dabei wohl nicht als Evaginationen eines die Eizellen enthaltenden Coelomsackes, sondern entweder als randliche Abfaltungen des Genitalcoeloms, oder als laterale Evaginationen, die retrograd sekundären Kontakt zum germinativen Teil aufnehmen, eine Beobachtung, die noch weiterer Klärung bedarf. Sehr erleichtert durch die Modellserie wurde auch die Planung von Semi- und Ultradünnschnittserien ausgewählter Strukturen, die histologische und funktionelle Einsichten lieferten. So konnte das Einsetzen der Meiose in der Tritonymphe, die Aufnahme von Dottervorstufen aus dem Fettkörper in die Eizelle durch Mikrovilli und ‘coated pitsˊ, die Ablagerung von Eihüllenmaterial und dessen Verfestigung beim Übergang ins Ovidukt beobachtet werden. Durch diese Erkenntnisse konnte eine Nomenklatur des Genitalsystems begründet werden, das Ovar als funktionell panoistisch klassifiziert und die Ovidukte als geschützter Raum der Embryonalentwicklung beschrieben. Insgesamt ergeben sich Hinweise darauf, dass der Reproduktionsmodus durch Wegfall der Befruchtung die anatomische Verdichtung und Verschränkung der Prozesse erlaubt, was eine konstant hohe Reproduktionsrate auch unter kurzfristig wechselnden Lebensbedingungen ermöglicht. Mit der vorgestellten Methodenauswahl konnte der Reproduktionsmodus der Thelytokie mit terminaler Fusion und invertierter (postreduktionaler) Meiose im funktionalen Zusammenhang dargestellt, und A. longisetosus als aussichtsreiches Modellsystem für auch über den Bereich der Cheliceraten hinausweisenden Fragestellungen vorgestellt werden

Partenogeneettisen lajin evoluutiomahdollisuudet – uusia havaintoja suopursukempiltä, Cacopsylla ledi, (Flor 1861) (Hemiptera, Sternorrhyncha, Psylloidea)

Suopursukemppejä (Cacopsylla ledi, (Flor 1861)) tavataan pohjoisella pallonpuoliskolla aina Fennoskandiasta Alaskaan. Ne lisääntyvät obligatorisella partenogeneesillä. Tarkemmin ottaen kempit lisääntyvät telytokisesti, eli naaraat tuottavat naarasyksilöitä hedelmöittymättömistä munasoluista. Telytokisten lajien populaatioissa voi esiintyä naaraiden ohella niin kutsuttuja harvinaisia koiraita, joita on löydetty myös suopursukemppien populaatioista. Harvinaiset koiraat voivat olla funktionaalisia, eli ne tuottavat normaaleja toimivia gameetteja, tai ei-funktionaalisia, jolloin niiden gameetit ovat toimimattomia. Suopursukempillä harvinaisten koiraiden lisäksi samaisista populaatioista on löydetty myös harvinaisia diploideja naaraita triploidien partenogeneettisesti lisääntyvien naaraiden ohella. Partenogeneettistä lisääntymistä on pidetty pitkään evolutiivisena umpikujana, sillä syntyvät jälkeläiset ovat emonsa klooneja. Biseksuaalisen lisääntymisen on todettu antavan lajille suuremman evolutiivisen potentiaalin rekombinaation myötä. Tämän tutkimuksen tarkoituksena oli selvittää, voisivatko partenogeneettisissä populaatioissa esiintyvät harvinaiset funktionaaliset koiraat ja harvinaiset diploidit naaraat lisääntyä keskenään. Tutkimuksen aineistona käytettiin Varinais-Suomesta Lammenrahkalta ja Laustinrahkalta sekä Lapista Sevettijärveltä kerättyjä naaraita ja koiraita. Naaraiden ploidiataso määritettiin sytologisesti, minkä jälkeen niille tehtiin haplotyyppianalyysi. Haplotyyppianalyysissä sekvensoitiin 638 nukleotidin pituinen mitokondriaalinen COI -geenialue. Sevettijärven populaation todettiin olevan partenogeneettinen. Lammenrahkan ja Laustinrahkan populaatioista puolestaan löydettiin funktionaalisia koiraita ja diploideja naaraita, jotka edustivat kokonaan omaa haplotyyppiään, mistä voitiin päätellä, että näissä kahdessa populaatiossa esiintyi aitoa biseksuaalista lisääntymistä partenogeneettisen lisääntymisen rinnalla. Kyseessä ovat ensimmäiset partenogeneettisen lajin luonnosta löydetyt populaatiot, joissa biseksuaalinen lisääntyminen on voitu todentaa kromosomianalyysin ja COI-haplotyyppianalyysin avulla. Lammenrahkan populaatiossa biseksuaalinen lisääntyminen on lähes syrjäyttänyt partenogeneettisen lisääntymisen, mitä ilmeisimmin paremman sopeutumiskykynsä ansiosta. Partenogeneettisten naarai-den tuottamat harvinaiset funktionaaliset koiraat ja diploidit naaraat antavat lajille mahdollisuuden kehittyä joko uudeksi partenogeneettiseksi, tai jopa biseksuaaliseksi lajiksi

Effective purifying selection in ancient asexual oribatid mites.

Sex is beneficial in the long term because it can prevent mutational meltdown through increased effectiveness of selection. This idea is supported by empirical evidence of deleterious mutation accumulation in species with a recent transition to asexuality. Here, we study the effectiveness of purifying selection in oribatid mites which have lost sex millions of years ago and diversified into different families and species while reproducing asexually. We compare the accumulation of deleterious nonsynonymous and synonymous mutations between three asexual and three sexual lineages using transcriptome data. Contrasting studies of young asexual lineages, we find evidence for strong purifying selection that is more effective in asexual as compared to sexual oribatid mite lineages. Our results suggest that large populations likely sustain effective purifying selection and facilitate the escape of mutational meltdown in the absence of sex. Thus, sex per se is not a prerequisite for the long-term persistence of animal lineages.Asexual reproduction is thought to be an evolutionary dead end in eukaryotes because deleterious mutations will not be purged effectively. Here, Brandt and colleagues show that anciently asexual oribatid mites in fact have reduced accumulation of deleterious mutations compared to their sexual relatives

Characteristics of parthenogenesis in Cacopsylla ledi (Flor, 1861) (Hemiptera, Sternorryncha, Psylloidea): cytological and molecular approaches

Characteristics of parthenogenesis in Cacopsylla ledi (Flor, 1861) were analyzed using cytological and molecular approaches. In all three populations studied from Finland, i.e. Turku, Kustavi and Siikajoki, males were present at a low frequency but were absent from a population from Vorkuta, Russia. In a follow-up study conducted in the Turku population during 2010–2016, the initial frequency of males was ca. 10 % and showed no intraseasonal variation, but then dramatically decreased down to approximately 1–2 % level in seasons 2015–2016. Male meiosis was chiasmate with some traces of chromosomal fragmentation and subsequent fusions. In most females, metaphase in mature eggs included 39 univalent chromosomes which indicated apomictic triploidy. Only a small fraction of females was diploid with 13 chiasmate bivalents. The frequency of diploid females approximately equaled that of males. COI barcode analyses showed that triploid females (N = 57) and diploids (7 females and 5 males) displayed different haplotypes, demonstrating that triploid females reproduced via obligate parthenogenesis. The rarity of diploids, along with the lack of males’ preference towards diploid females, suggested that most likely diploids were produced by rare triploid females which shared the same haplotype with the diploids (not found in the present analysis). Minimum haplotype diversity was detected in the Turku population, but it was much higher in Vorkuta with some indication for the mixed origin of the population. We suggest that functional diploids produced in a parthenogenetic population can give rise either to a new parthenogenetic lineage or even to a new bisexual species.</p