An Opiliones-specific ultraconserved element probe set with a near-complete family-level phylogeny

Two new species of Icaleptes (Opiliones: Laniatores: Icaleptidae) from Sierra Nevada de Santa Marta, Colombia

The genus Icaleptes was proposed by Kury & Pérez-González in 2002 to accommodate a single Colombian species, Icaleptes malkini, collected in the southeastern slope of Sierra Nevada de Santa Marta, Cesar Department. In this study, we describe two new species for this previously monotypic genus collected on the northwestern slope of the Sierra Nevada de Santa Marta, in the department of Magdalena. The new species Icaleptes dimorphicus sp. nov. and Icaleptes armasi sp. nov. were included within Icaleptes based on external and genital similarities such as male scutum magnum continuously convex and lacking the sulci; pedipalps with highly reduced setae; chelicerae stout and unarmed with a low, wide bulla; capsula externa of the penis modified into a robust stragulum with two widely separated apical lobes and a wide capsula interna visible from the dorsal aspect with a well-developed parastylar collar. In contrast to Icaleptes malkini, the two new species have the ventral plate of the penis differentiated into two regions, which we interpreted here as a wide pergula basally and a short stout rutrum apically. The new species also have other remarkable sexual dimorphisms such as males with a strong protuberance on coxa IV, an arched movable finger in the chelicerae, and enlarged basitarsomeres on leg III. The modification of coxa IV in males is a strong diagnostic character that facilitates the identification of both new species. The description of two new species that are closely related to the type species Icaleptes malkini helps us to understand the morphological variation of the current concept of Icaleptidae.

The Evolutionary Biology of Chelicerata

Chelicerata constitutes an ancient, biodiverse, and ecologically significant group of Arthropoda. The study of chelicerate evolution has undergone a renaissance in the past decade, resulting in major changes to our understanding of the higher-level phylogeny and internal relationships of living orders. Included among these conceptual advances are the discoveries of multiple whole-genome duplication events in a subset of chelicerate orders, such as horseshoe crabs, spiders, and scorpions. As a result, longstanding hypotheses and textbook scenarios of chelicerate evolution, such as the monophyly of Arachnida and a single colonization of land by the common ancestor of arachnids, have come into contention. The retention of ancient, duplicated genes across this lineage also offers fertile ground for investigating the role of gene duplication in chelicerate macroevolution. This new frontier of investigation is paralleled by the timely establishment of the first gene editing protocols for arachnid models, facilitating a new generation of experimental approaches.

Robustness to Leg Loss in Opiliones: A Review and Framework Considerations for Future Research

Animals have evolved behavioral and morphological traits that allow them to respond to environmental challenges. However, these traits may have long-term consequences that could impact an animal's performance, fitness, and welfare. Several species in a group of the arachnid order of Opiliones release their legs voluntarily to escape predators. These animals use their legs for locomotion, sensation, and reproduction. Here, we first compile data across species in the suborder Eupnoi, showing that more than half of individuals are found missing legs. Then, we review recent work on the ultimate and proximate implications of leg loss in Opiliones. Field and laboratory experiments showed that leg loss (a) did not affect their survival or mating success and (b) compromised the kinematics and energetics of locomotion, but individuals recovered velocity and acceleration quickly. These findings demonstrate that these animals display robustness, that is, the ability to withstand and overcome the potential consequences of bodily damage. This may explain why leg loss is so prevalent in Opiliones. Additionally, we encourage researchers to consider expanding their hypotheses beyond traditional adaptationist and ableist lenses and incorporate a comprehensive examination of animal welfare when studying animals' responses to bodily damage. Finally, we highlight avenues for future research in Opiliones, namely assessing how individuals move in three-dimensional environments, the neural plasticity aiding recovery post-leg loss, applications for bio-inspired design, and evidence-based animal welfare measures.

Reassessing the phylogeny of Cyphophthalmi with phylogenomics: A UCE-based phylogeny of mite harvesters (Opiliones)

Cyphophthalmi (the mite harvesters) are a group of Opiliones with broad interest due to their species being classic examples of short-range endemics and displaying model biogeographical patterns for poor dispersers. Cyphophthalmi phylogeny has received attention using morphology, Sanger-based sequencing data, or transcriptomics. Here we turn to a new type of data, ultraconserved elements (UCEs) and provide a first phylogeny for the entire suborder Cyphophthalmi using such data and including representatives from 36 of the 46 currently recognized genera. Phylogenetic analysis of four occupancy matrices (50%, 75%, 90% and 95%), for a total of 840, 567, 129, and 23 loci, respectively, yielded a well resolved phylogeny with monophyly of Pettalidae, Parasironidae, Stylocellidae and Troglosironidae. However, Neogoveidae appeared paraphyletic with respect to Ogoveidae in all datasets and to Troglosironidae in some, and the traditional Sironidae, which was monophyletic, now appeared paraphyletic with respect to the recently erected family Parasironidae. Our phylogenomic results using UCE data resolve the position of several problematic genera (e.g., Pettalus) and add support to other parts of the tree that received low support in Sanger-based phylogenies. Our work also stresses the possibility to add museum samples to phylogenies although methods for optimizing DNA yield from such small-bodied specimens need further improvement. Finally, this backbone phylogeny demonstrates the feasibility of an all-species phylogeny using UCEs for Cyphophthalmi, and by extension, for all Opiliones.

Testing ultraconserved elements (UCEs) for phylogenetic inference across bivalves (Mollusca: Bivalvia)

Bivalves constitute an important resource for fisheries and as cultural objects. Bivalve phylogenetics has had a long tradition using both morphological and molecular characters, and genomic resources are available for a good number of commercially important species. However, relationships among bivalve families have been unstable and major conflicting results exist between mitogenomics and results based on Sanger-based amplicon sequencing or phylotranscriptomics. Here we design and test an ultraconserved elements probe set for the class Bivalvia with the aim to use hundreds of loci without the need to sequence full genomes or transcriptomes, which are expensive and complex to analyze, and to open bivalve phylogenetics to museum specimens. Our probe set successfully captured 1,513 UCEs for a total of 263,800 bp with an average length of 174.59 ± 3.44 per UCE (ranging from 28 to 842 bp). Phylogenetic testing of this UCE probe set across Bivalvia and within the family Donacidae using different data matrices and methods for phylogenetic inference shows promising results at multiple taxonomic levels. In addition, our probe set was able to capture large numbers of UCEs for museum specimens collected before 1900 and from DNAs properly stored, of which many museums and laboratories are well stocked. Overall, this constitutes a novel and useful resource for bivalve phylogenetics.

New species of Paktongius and convergent evolution of the gonyleptoid-like habitus in Southeast Asian Assamiidae (Opiliones: Laniatores)

The armored harvestman family Assamiidae (Arachnida: Opiliones: Laniatores) is widely distributed throughout the Old World tropics, specifically throughout tropical Asia and Central Africa. However, the systematics and intrafamilial relationships of the group remain poorly understood. This can be largely attributed to the complicated taxonomic history of the group, which is exemplified by poorly supported subfamily classifications and the prevalence of monotypic genera. Here, we describe four new species of the formerly monotypic genus Paktongius Suzuki, 1969, using specimens collected from Laos, Thailand, and West Malaysia, suggesting a degree of microendemism within the group, which underscores the need for greater sampling of the southeast Asian arachnofauna. Recent phylogenetic analysis has also suggested that Mysorea thaiensis Suzuki, 1985 nests within a clade composed of Paktongius distinctus Suzuki, 1969 and the species described herein (P. suzukii sp. nov., P. spiculosus sp. nov., P. paritensis sp. nov., P. furculus sp. nov.). We therefore transfer Mysorea thaiensis to Paktongius (P. thaiensis comb. nov.). We also comment on the unique morphology of this highly derived group of harvestmen, which appears to suggest convergent evolution of the gonyleptoid-like morphology, complete with the characteristic exaggerated leg four coxae and laterally expanded scutum.