A Novel Expression Domain of extradenticle Underlies the Evolutionary Developmental Origin of the Chelicerate Patella.

Neofunctionalization of duplicated gene copies is thought to be an important process underlying the origin of evolutionary novelty and provides an elegant mechanism for the origin of new phenotypic traits. One putative case where a new gene copy has been linked to a novel morphological trait is the origin of the arachnid patella, a taxonomically restricted leg segment. In spiders, the origin of this segment has been linked to the origin of the paralog dachshund-2, suggesting that a new gene facilitated the expression of a new trait.

A novel expression domain of underlies the evolutionary developmental origin of the chelicerate patella.

Neofunctionalization of duplicated gene copies is thought to be an important process underlying the origin of evolutionary novelty and provides an elegant mechanism for the origin of new phenotypic traits. One putative case where a new gene copy has been linked to a novel morphological trait is the origin of the arachnid patella, a taxonomically restricted leg segment. In spiders, the origin of this segment has been linked to the origin of the paralog , suggesting that a new gene facilitated the expression of a new trait.

Vestigial organs alter fossil placements in an ancient group of terrestrial chelicerates.

Vestigial organs provide a link between ancient and modern traits and therefore have great potential to resolve the phylogeny of contentious fossils that bear features not seen in extant species. Here we show that extant daddy-longlegs (Arachnida, Opiliones), a group once thought to possess only one pair of eyes, in fact additionally retain a pair of vestigial median eyes and a pair of vestigial lateral eyes. Neuroanatomical gene expression surveys of eye-patterning transcription factors, opsins, and other structural proteins in the daddy-longlegs Phalangium opilio show that the vestigial median and lateral eyes innervate regions of the brain positionally homologous to the median and lateral eye neuropils, respectively, of chelicerate groups like spiders and horseshoe crabs.

A plurality of morphological characters need not equate with phylogenetic accuracy: A rare genomic change refutes the placement of Solifugae and Pseudoscorpiones in Haplocnemata.

Recent advances in higher-level invertebrate phylogeny have leveraged shared features of genomic architecture to resolve contentious nodes across the tree of life. Yet, the interordinal relationships within Chelicerata have remained recalcitrant given competing topologies in recent molecular analyses. As such, relationships between topologically unstable orders remain supported primarily by morphological cladistic analyses.

Dual Functions of labial Resolve the Hox Logic of Chelicerate Head Segments.

Despite an abundance of gene expression surveys, comparatively little is known about Hox gene function in Chelicerata. Previous investigations of paralogs of labial (lab) and Deformed (Dfd) in a spider have shown that these play a role in tissue maintenance of the pedipalp segment (lab-1) and in patterning the first walking leg identity (Dfd-1), respectively. However, extrapolations of these data across chelicerates are hindered by the existence of duplicated Hox genes in arachnopulmonates (e.

In the land of the blind: Exceptional subterranean speciation of cryptic troglobitic spiders of the genus Tegenaria (Araneae: Agelenidae) in Israel.

Caves have long been recognized as a window into the mechanisms of diversification and convergent evolution, due to the unique conditions of isolation and life in the dark. These lead to adaptations and reduce dispersal and gene flow, resulting in high levels of speciation and endemism. The Israeli cave arachnofauna remains poorly known, but likely represents a rich assemblage.

Recent speciation and phenotypic plasticity within a parthenogenetic lineage of levantine whip spiders (Chelicerata: Amblypygi: Charinidae).

Caves constitute ideal study systems for investigating adaptation and speciation, as the abiotic conditions shared by aphotic habitats exert a set of environmental filters on their communities. Arachnids constitute an important component of many cave ecosystems worldwide. We investigated the population genomics of two whip spider species: Sarax ioanniticus, a widely distributed parthenogenetic species found across the eastern Mediterranean; and S.

Phylogenomics of Scorpions Reveal Contemporaneous Diversification of Scorpion Mammalian Predators and Mammal-Active Sodium Channel Toxins.

Scorpions constitute a charismatic lineage of arthropods and comprise more than 2500 described species. Found throughout various tropical and temperate habitats, these predatory arachnids have a long evolutionary history, with a fossil record that began in the Silurian. While all scorpions are venomous, the asymmetrically diverse family Buthidae harbors nearly half the diversity of extant scorpions, and all but one of the 58 species that are medically significant to humans.

Eggs to long-legs: embryonic staging of the harvestman Phalangium opilio (Opiliones), an emerging model arachnid.

Background: The comparative embryology of Chelicerata has greatly advanced in recent years with the integration of classical studies and genetics, prominently spearheaded by developmental genetic works in spiders. Nonetheless, the understanding of the evolution of development and polarization of embryological characters in Chelicerata is presently limited, as few non-spider species have been well studied. A promising focal species for chelicerate evo-devo is the daddy-long-legs (harvestman) Phalangium opilio, a member of the order Opiliones.

Comprehensive Species Sampling and Sophisticated Algorithmic Approaches Refute the Monophyly of Arachnida.

Deciphering the evolutionary relationships of Chelicerata (arachnids, horseshoe crabs, and allied taxa) has proven notoriously difficult, due to their ancient rapid radiation and the incidence of elevated evolutionary rates in several lineages. Although conflicting hypotheses prevail in morphological and molecular data sets alike, the monophyly of Arachnida is nearly universally accepted, despite historical lack of support in molecular data sets. Some phylotranscriptomic analyses have recovered arachnid monophyly, but these did not sample all living orders, whereas analyses including all orders have failed to recover Arachnida.

The genome of a daddy-long-legs (Opiliones) illuminates the evolution of arachnid appendages.

Chelicerate arthropods exhibit dynamic genome evolution, with ancient whole-genome duplication (WGD) events affecting several orders. Yet, genomes remain unavailable for a number of poorly studied orders, such as Opiliones (daddy-long-legs), which has hindered comparative study. We assembled the first harvestman draft genome for the species , which bears elongate, prehensile appendages, made possible by numerous distal articles called tarsomeres.

Taxonomic Sampling and Rare Genomic Changes Overcome Long-Branch Attraction in the Phylogenetic Placement of Pseudoscorpions.

Long-branch attraction is a systematic artifact that results in erroneous groupings of fast-evolving taxa. The combination of short, deep internodes in tandem with long-branch attraction artifacts has produced empirically intractable parts of the Tree of Life. One such group is the arthropod subphylum Chelicerata, whose backbone phylogeny has remained unstable despite improvements in phylogenetic methods and genome-scale data sets.

Systemic paralogy and function of retinal determination network homologs in arachnids.

Background: Arachnids are important components of cave ecosystems and display many examples of troglomorphisms, such as blindness, depigmentation, and elongate appendages. Little is known about how the eyes of arachnids are specified genetically, let alone the mechanisms for eye reduction and loss in troglomorphic arachnids. Additionally, duplication of Retinal Determination Gene Network (RDGN) homologs in spiders has convoluted functional inferences extrapolated from single-copy homologs in pancrustacean models.

Phylogenomic Resolution of Sea Spider Diversification through Integration of Multiple Data Classes.

Despite significant advances in invertebrate phylogenomics over the past decade, the higher-level phylogeny of Pycnogonida (sea spiders) remains elusive. Due to the inaccessibility of some small-bodied lineages, few phylogenetic studies have sampled all sea spider families. Previous efforts based on a handful of genes have yielded unstable tree topologies.

Genomic resources and toolkits for developmental study of whip spiders (Amblypygi) provide insights into arachnid genome evolution and antenniform leg patterning.

Background: The resurgence of interest in the comparative developmental study of chelicerates has led to important insights, such as the discovery of a genome duplication shared by spiders and scorpions, inferred to have occurred in the most recent common ancestor of Arachnopulmonata (a clade comprising the five arachnid orders that bear book lungs). Nonetheless, several arachnid groups remain understudied in the context of development and genomics, such as the order Amblypygi (whip spiders). The phylogenetic position of Amblypygi in Arachnopulmonata posits them as an interesting group to test the incidence of the proposed genome duplication in the common ancestor of Arachnopulmonata, as well as the degree of retention of duplicates over 450 Myr.

Two new species of Manahunca, redescription of its type species, current conservation status of the genus and a survey of male glands in Stenostygninae (Opiliones: Laniatores: Biantidae).

Manahunca bielawskii Šilhavý, 1973, the type species of the genus Manahunca Šilhavý, 1973, is redescribed based on abundant material from the type locality, including new data on its morphological variability and penis morphology. A neotype for M. bielawskii is herein designated due to the unknown whereabouts of the original holotype.

The sensory equipment of a sandokanid: An extreme case of tarsal reduction in harvestmen (Arachnida, Opiliones, Laniatores).

The study of sensory structures has the potential to provide insights into the natural history and evolution of animals. The sensory structures of arachnids are usually concentrated on the pedipalps (the tritocerebral appendages) or on the distal podomere (tarsus) of the anterior walking legs, the latter being the case for armored harvestmen (Opiliones, Laniatores). Therefore, modifications of the tarsus could have direct impacts on the sensory equipment of these animals.

Ultrastructure of chemoreceptive tarsal sensilla in an armored harvestman and evidence of olfaction across Laniatores (Arachnida, Opiliones).

Harvestmen (Arachnida, Opiliones) are especially dependent on chemical cues and are often regarded as animals that rely mainly on contact chemoreception. Information on harvestman sensilla is scarce when compared to other arachnid orders, especially concerning internal morphology. Using scanning (SEM) and transmission (TEM) electron microscopy, we investigated tarsal sensilla on the distal tarsomeres (DT) of all leg pairs in Heteromitobates discolor (Laniatores, Gonyleptidae).

Walk it off: predictive power of appendicular characters toward inference of higher-level relationships in Laniatores (Arachnida: Opiliones).

Morphological characters are essential for establishing phylogenetic relationships, delimiting higher-level taxa, and testing phylogenetic relationships inferred from molecular sequence data. In cases where relationships between large clades remain unresolved, it becomes imperative to establish which character systems are sound predictors of phylogenetic signal. In the case of Laniatores, the largest suborder of Opiliones, some superfamilial relationships remain unresolved or unsupported, and traditionally employed phenotypic characters are typically of utility only at the family level.