Ultrastructure of spermatozoa of solifuges (Arachnida, Solifugae): Possible characters for their phylogeny?

Neglected no longer: Phylogenomic resolution of higher-level relationships in Solifugae

Advanced sequencing technologies have expedited resolution of higher-level arthropod relationships. Yet, dark branches persist, principally among groups occurring in cryptic habitats. Among chelicerates, Solifugae ("camel spiders") is the last order lacking a higher-level phylogeny and have thus been historically characterized as "neglected [arachnid] cousins". Though renowned for aggression, remarkable running speed, and xeric adaptation, inferring solifuge relationships has been hindered by inaccessibility of diagnostic morphological characters, whereas molecular investigations have been limited to one of 12 recognized families. Our phylogenomic dataset via capture of ultraconserved elements sampling all extant families recovered a well-resolved phylogeny, with two distinct groups of New World taxa nested within a broader Paleotropical radiation. Divergence times using fossil calibrations inferred that Solifugae radiated by the Permian, and most families diverged prior to the Paleogene-Cretaceous extinction, likely driven by continental breakup. We establish Boreosolifugae new suborder uniting five Laurasian families, and Australosolifugae new suborder uniting seven Gondwanan families using morphological and biogeographic signal.

Outsourcing a visual neuropil - The central visual system of the median eyes of Galeodes granti Pocock, 1903 (Arachnida: Solifugae)

Only a few studies have examined the central visual system of Solifugae until now. To get new insights suitable for phylogenetic analysis we studied the R-cell (or retinula cell) projections and visual neuropils of Galeodes granti using various methods. G. granti possesses large median eyes and rudimentary lateral eyes. In this study, only the R-cells and neuropils of the median eyes were successfully stained. The R-cells terminate in two distinct visual neuropils. The first neuropil is located externally to the protocerebrum directly below the retina, the second neuropil lies in the cell body rind of the protocerebrum, and immediately adjacent is the arcuate body. This layout of the median eye visual system differs from Arachnopulmonata (Scorpiones + Tetrapulmonata). However, there are several similarities with Opiliones. In both, (1) the R-cells are connected to a first and second visual neuropil and not to any other region of the brain, (2) the first neuropil is not embedded in the cell body rind of the protocerebrum, it is rather external to the protocerebrum, (3) the second visual neuropil is embedded in the cell body rind, and (4) the second neuropil abuts the arcuate body. These findings may provide important new characters for the discussion on arachnid phylogeny.

Mitochondrial DNA phylogeny of camel spiders (Arachnida: Solifugae) from Iran

In the present study, the mitochondrial DNA phylogeny of five solifuge families of Iran is presented using phylogenetic analysis of mitochondrial cytochrome c oxidase, subunit 1 (COI) sequence data. Moreover, we included available representatives from seven families from GenBank to examine the genetic distance between Old and New World taxa and test the phylogenetic relationships among more solifuge families. Phylogenetic relationships were reconstructed based on the two most probabilistic methods, Maximum Likelihood (ML) and Bayesian inference (BI) approaches. Resulting topologies demonstrated the monophyly of the families Daesiidae, Eremobatidae, Galeodidae, Karschiidae and Rhagodidae, whereas the monophyly of the families Ammotrechidae and Gylippidae was not supported. Also, within the family Eremobatidae, the subfamilies Eremobatinae and Therobatinae and the genus Hemerotrecha were paraphyletic or polyphyletic. According to the resulted topologies, the taxonomic placements of Trichotoma michaelseni (Gylippidae) and Nothopuga sp. 1 (Ammotrechidae) are still remain under question and their revision might be appropriate. According to the results of this study, within the family Galeodidae, the validity of the genus Galeodopsis is supported, while the validity of the genus Paragaleodes still remains uncertain. Moreover, our results revealed that the species Galeodes bacillatus, and Rhagodes melanochaetus are junior synonyms of G. caspius, and R. eylandti, respectively.

Fine structure of the male genital system of the predatory mite Rhagidia halophila (Rhagidiidae, Prostigmata, Actinotrichida)

The male genital system of the actinotrichid mite Rhagidia halophila is described and compared with other mites and arachnids. The large testes are composed of germinal and glandular parts and produce numerous small sperm cells. The glandular parts are connected via a testicular bridge. Spermiogenesis occurs in cysts containing spermatids in equal stages of development. Cysts of spermatids are embedded in huge somatic cells. The nuclei of the spermatids loose their envelope. Mature sperm cells are simple exhibiting a ring-shaped chromatin body and lacking an acrosomal complex. They are most similar to the sperm cells of the related mite Linopodes motatorius. The spermatopositor contains the ejaculatory duct divided into a dorsal channel and a ventral channel that are connected via a narrow passage. At its distal end, the spermatopositor is divided into three eugenital lips. The function of the spermatopositor during deposition of the peculiar thread-like spermatophores is discussed. Details of the sensilla of the spermatopositor and the progenital lips are reported. The genital papillae located on the inner side of the progenital lips exhibit characteristics of cells performing transport of ions and/or water. The results confirm the overall similarity of actinotrichid genital systems, which is profoundly different from that of anactinotrichid mites. With reference to other Arachnida it is corroborated that testes and sperm structure of Actinotrichida are most similar to that of Solifugae. However, synapomorphies between sperm cells of Rhagidia and Solifugae that could suggest a closer relationship between these two taxa as was suggested in earlier studies were not recognizable. On the contrary, the sperm cells of Rh. halophila being devoid of an acrosomal complex appeared to be more apomorphic than those of many other actinotrichid mites as well as Solifugae.

Evolutionary morphology of the male reproductive system, spermatozoa and seminal fluid of spiders (Araneae, Arachnida)--current knowledge and future directions

The male reproductive system and spermatozoa of spiders are known for their high structural diversity. Spider spermatozoa are flagellate and males transfer them to females in a coiled and encapsulated state using their modified pedipalps. Here, we provide a detailed overview of the present state of knowledge of the primary male reproductive system, sperm morphology and the structural diversity of seminal fluids with a focus on functional and evolutionary implications. Secondly, we conceptualized characters for the male genital system, spermiogenesis and spermatozoa for the first time based on published and new data. In total, we scored 40 characters for 129 species from 56 families representing all main spider clades. We obtained synapomorphies for several taxa including Opisthothelae, Araneomorphae, Dysderoidea, Scytodoidea, Telemidae, Linyphioidea, Mimetidae, Synotaxidae and the Divided Cribellum Clade. Furthermore, we recovered synspermia as a synapomorphy for ecribellate Haplogynae and thus propose Synspermiata as new name for this clade. We hope that these data will not only contribute to future phylogenetic studies but will also stimulate much needed evolutionary studies of reproductive systems in spiders.

A review of Cunaxidae (Acariformes, Trombidiformes): Histories and diagnoses of subfamilies and genera, keys to world species, and some new locality records

Cunaxidae are predaceous mites found in a variety of habitats. This work provides comprehensive keys to world subfamilies, genera, and species. Diagnoses and historical reviews are provided for subfamilies and genera. Cunaxa boneti, C. denmarki, C. exoterica, C. floridanus, C. lehmanae, C. lukoschusi, C. metzi, C. myabunderensis, C newyorkensis, C. rackae, C. reevesi, and C. reticulatus are moved to Rubroscirus and C. otiosus, C. valentis, and C. rasile are returned to Rubroscirus. Cunaxoides neopectinatus is moved to Pulaeus. Neocunaxoides pradhani and N. gilbertoi are transferred to Scutopalus. Pulaeus minutus and P. subterraneus are moved to Lupaeus. Pseudobonzia bakari, P. malookensis, and P. shamshadi are transferred to Neobonzia. Dactyloscirus bifidus is transferred to Armascirus. Scirula papillata is reported from the Western Hemisphere for the first time. Armascirus ozarkensis, A. primigenius, and Dactyloscirus dolichosetosus are reported from new localities.

Pseudoscorpion mitochondria show rearranged genes and genome-wide reductions of RNA gene sizes and inferred structures, yet typical nucleotide composition bias

BACKGROUND

Pseudoscorpions are chelicerates and have historically been viewed as being most closely related to solifuges, harvestmen, and scorpions. No mitochondrial genomes of pseudoscorpions have been published, but the mitochondrial genomes of some lineages of Chelicerata possess unusual features, including short rRNA genes and tRNA genes that lack sequence to encode arms of the canonical cloverleaf-shaped tRNA. Additionally, some chelicerates possess an atypical guanine-thymine nucleotide bias on the major coding strand of their mitochondrial genomes.

RESULTS

We sequenced the mitochondrial genomes of two divergent taxa from the chelicerate order Pseudoscorpiones. We find that these genomes possess unusually short tRNA genes that do not encode cloverleaf-shaped tRNA structures. Indeed, in one genome, all 22 tRNA genes lack sequence to encode canonical cloverleaf structures. We also find that the large ribosomal RNA genes are substantially shorter than those of most arthropods. We inferred secondary structures of the LSU rRNAs from both pseudoscorpions, and find that they have lost multiple helices. Based on comparisons with the crystal structure of the bacterial ribosome, two of these helices were likely contact points with tRNA T-arms or D-arms as they pass through the ribosome during protein synthesis.The mitochondrial gene arrangements of both pseudoscorpions differ from the ancestral chelicerate gene arrangement. One genome is rearranged with respect to the location of protein-coding genes, the small rRNA gene, and at least 8 tRNA genes. The other genome contains 6 tRNA genes in novel locations. Most chelicerates with rearranged mitochondrial genes show a genome-wide reversal of the CA nucleotide bias typical for arthropods on their major coding strand, and instead possess a GT bias. Yet despite their extensive rearrangement, these pseudoscorpion mitochondrial genomes possess a CA bias on the major coding strand. Phylogenetic analyses of all 13 mitochondrial protein-coding gene sequences consistently yield trees that place pseudoscorpions as sister to acariform mites.

CONCLUSION

The well-supported phylogenetic placement of pseudoscorpions as sister to Acariformes differs from some previous analyses based on morphology. However, these two lineages share multiple molecular evolutionary traits, including substantial mitochondrial genome rearrangements, extensive nucleotide substitution, and loss of helices in their inferred tRNA and rRNA structures.

The male reproductive system of Zorotypus caudelli Karny (Zoraptera): Sperm structure and spermiogenesis

Considering the overall uniformity of the morphology of Zoraptera, the structural diversity of the male genital system is remarkable. Structures related to the male reproductive system of Zorotypus caudelli differ profoundly from those of Zorotypus hubbardi. The testes are elongated rather than spherical, the seminal vesicle is apparently absent, and the deferent ducts are very long. A feature shared by these two species and other zorapterans examined is that the two accessory glands are closely adherent to each other and form a single large structure, from which the ejaculatory duct originates. This is a potential zorapteran autapomorphy. Another feature possibly present in the groundplan of the order is the strong elongation of the sperm cells. This may be connected with a reproductive strategy of males trying to avoid re-mating of females with other males after the first copulation. The extremely long and coiled spermathecal duct of Z. caudelli and other zorapteran species is possibly correlated with the sperm elongation, and both features combined may result in a sexual isolating mechanism. The short duration of mating of Zorotypus barberi and Zorotypus gurneyi suggests that the male introduces sperm into the female tract up to the opening of the spermathecal duct using their long coiled aedeagus. A thick glycocalyx around the sperm in the distal part of the deferent ducts probably protects the sperm cells during their forward progression towards the long spermathecal duct, and is removed when they reach the apical receptacle. The spermatogenesis of Z. caudelli follows a pattern commonly found in insects, but differs distinctly from that of Z. hubbardi in the number of spermatids in each sperm cyst. An unusual and possibly autapomorphic feature of Z. caudelli is a disconnection of sub-tubules A and B at the level of microtubule doublets 1 and 6 of the mature sperm cells. It is conceivable that this results in a shorter period of sperm motility. The character combination found in different zorapteran species supports the view that the sperm, a very compact functional unit, does not evolve as a unit, but like in other more complex body regions, sperm components can also be modified independently from each other. This results in different mosaic patterns of plesiomorphic and derived features in a very compact entity in different species of the very small and otherwise uniform order Zoraptera. In Z. caudelli, for instance, the bi-layered acrosome and small accessory bodies are plesiomorphic states among several others, whereas the mitochondrial derivatives and the elongate nucleus are apparently derived conditions. Other combinations likely occur in other zorapteran species. Only few but noteworthy sperm characters indicate possible phylogenetic affinities of Zoraptera. A possible synapomorphic feature, the presence of dense laminae radiating in a cartwheel array between neighbouring centriolar triplets, is shared with Phasmatodea and Embioptera. Another potential synapomorphy shared with Phasmatodea is the presence of 17 protofilaments in the tubular wall of the outer accessory microtubules.

Sperm accessory microtubules suggest the placement of Diplura as the sister-group of Insecta s.s

Sperm ultrastructure and spermiogenesis of the dipluran Japygidae (Japyx solifugus, Metajapyx braueri and Occasjapyx japonicus) and Campodeidae (Campodea sp.) were studied with the aim of looking for potential characters for the reconstruction of the phylogenetic relationships of basal hexapods. Both Japygidae and Campodeidae share a common sperm axonemal model 9+9+2, provided with nine accessory microtubules. These microtubules, however, after their formation lose the usual position around the 9+2 and migrate between the two mitochondria. In Japygidae, four of these microtubules are very short and were observed beneath the nucleus after negative staining and serial sections. Accessory microtubules have 13 protofilaments in their tubular wall. Diplura have a sperm morphology which is very different from that of the remaining Entognatha (Protura+Collembola). On the basis of the present results, the presence of accessory microtubules suggests that Diplura are the sister-group of the Insecta s.s.. Moreover, Japygidae and Campodeidae differ with regards to the relative position of the sperm components, the former having the axoneme starting from beneath the nucleus (above which sits the short acrosome), while the latter having a long apical acrosome and a nucleus running parallel with the proximal part of the axoneme. The present study also allowed to redescribe the male genital system of Japyx.

Spermatozoa of an Old World Ricinulei (Ricinoides karschii, Ricinoidae) with notes about the relationships of Ricinulei within the Arachnida

The ultrastructure of spermatozoa is a valuable tool for phylogenetic and systematic studies. Ricinulei are enigmatic and poorly studied arachnids. So far, spermatozoa are only known from New World ricinuleids. The goals were to study, by means of light and transmission electron microcopy, the spermatozoa of an Old World species with regard to their phylogenetic implications, e.g., does the sperm structure contribute to the debated sister-group relationship of Acari and Ricinulei. The spermatozoa are coiled-flagellate and characterized by a cap-like acrosomal vacuole covered by electron-dense material, an elongated nucleus covered by a manchette of microtubules during spermiogenesis, an axoneme with a 9+2 microtubular pattern, a nuclear tube and axonemal basis which both originate underneath the acrosomal vacuole and cleistospermia as transfer form equipped with three intracellular plates. The data of the present study did not support a close relationship of Ricinulei and Acari which have aflagellate sperm with various synapomorphies as e.g., lacking nuclear envelopes/membranes in Actinotrichida (very similar to Solifugae) or vacuolated spermatozoa in Anactinotrichida. Affinities of Ricinulei are discussed in the light of the ultrastructure of arachnid spermatozoa.

Phylogenetic position of the acariform mites: sensitivity to homology assessment under total evidence

BACKGROUND

Mites (Acari) have traditionally been treated as monophyletic, albeit composed of two major lineages: Acariformes and Parasitiformes. Yet recent studies based on morphology, molecular data, or combinations thereof, have increasingly drawn their monophyly into question. Furthermore, the usually basal (molecular) position of one or both mite lineages among the chelicerates is in conflict to their morphology, and to the widely accepted view that mites are close relatives of Ricinulei.

RESULTS

The phylogenetic position of the acariform mites is examined through employing SSU, partial LSU sequences, and morphology from 91 chelicerate extant terminals (forty Acariformes). In a static homology framework, molecular sequences were aligned using their secondary structure as guide, whereby regions of ambiguous alignment were discarded, and pre-aligned sequences analyzed under parsimony and different mixed models in a Bayesian inference. Parsimony and Bayesian analyses led to trees largely congruent concerning infra-ordinal, well-supported branches, but with low support for inter-ordinal relationships. An exception is Solifugae + Acariformes (P. P = 100%, J. = 0.91). In a dynamic homology framework, two analyses were run: a standard POY analysis and an analysis constrained by secondary structure. Both analyses led to largely congruent trees; supporting a (Palpigradi (Solifugae Acariformes)) clade and Ricinulei as sister group of Tetrapulmonata with the topology (Ricinulei (Amblypygi (Uropygi Araneae))). Combined analysis with two different morphological data matrices were run in order to evaluate the impact of constraining the analysis on the recovered topology when employing secondary structure as a guide for homology establishment. The constrained combined analysis yielded two topologies similar to the exclusively molecular analysis for both morphological matrices, except for the recovery of Pedipalpi instead of the (Uropygi Araneae) clade. The standard (direct optimization) POY analysis, however, led to the recovery of trees differing in the absence of the otherwise well-supported group Solifugae + Acariformes.

CONCLUSIONS

Previous studies combining ribosomal sequences and morphology often recovered topologies similar to purely morphological analyses of Chelicerata. The apparent stability of certain clades not recovered here, like Haplocnemata and Acari, is regarded as a byproduct of the way the molecular homology was previously established using the instrumentalist approach implemented in POY. Constraining the analysis by a priori homology assessment is defended here as a way of maintaining the severity of the test when adding new data to the analysis. Although the strength of the method advocated here is keeping phylogenetic information from regions usually discarded in an exclusively static homology framework; it still has the inconvenience of being uninformative on the effect of alignment ambiguity on resampling methods of clade support estimation. Finally, putative morphological apomorphies of Solifugae + Acariformes are the reduction of the proximal cheliceral podomere, medial abutting of the leg coxae, loss of sperm nuclear membrane, and presence of differentiated germinative and secretory regions in the testis delivering their products into a common lumen.