An ultraconserved element probe set for velvet worms (Onychophora)

Onychophora are cryptic, soil-dwelling invertebrates known for their biogeographic affinities, diversity of reproductive modes, close phylogenetic relationship to arthropods, and peculiar prey capture mechanism. The 216 valid species of Onychophora are grouped into two families - Peripatopsidae and Peripatidae - and apart from a few relationships among major lineages within these two families, a stable phylogenetic backbone for the phylum has yet to be resolved. This has hindered our understanding of onychophoran biogeographic patterns, evolutionary history, and systematics. Neopatida, the Neotropical clade of peripatids, has proved particularly difficult, with recalcitrant nodes and low resolution, potentially due to rapid radiation of the group during the Cretaceous. Previous studies have had to compromise between number of loci and number of taxa due to limitations of Sanger sequencing and phylotranscriptomics, respectively. Additionally, aspects of their genome size and structure have made molecular phylogenetics difficult and data matrices have been affected by missing data. To address these issues, we leveraged recent, published transcriptomes and the first high quality genome for the phylum and designed a high affinity ultraconserved element (UCE) probe set for Onychophora. This new probe set, consisting of ∼ 20,000 probes that target 1,465 loci across both families, has high locus recovery and phylogenetic utility. Phylogenetic analyses recovered the monophyly of major clades of Onychophora and revealed a novel lineage from the Neotropics that challenges our current understanding of onychophoran biogeographic endemicity. This new resource could drastically increase the power of molecular datasets and potentially allow access to genomic scale data from archival museum specimens to further tackle the issues exasperating onychophoran systematics.

The venom and telopodal defence systems of the centipede Lithobius forficatus are functionally convergent serial homologues

BACKGROUND

Evolution of novelty is a central theme in evolutionary biology, yet studying the origins of traits with an apparently discontinuous origin remains a major challenge. Venom systems are a well-suited model for the study of this phenomenon because they capture several aspects of novelty across multiple levels of biological complexity. However, while there is some knowledge on the evolution of individual toxins, not much is known about the evolution of venom systems as a whole. One way of shedding light on the evolution of new traits is to investigate less specialised serial homologues, i.e. repeated traits in an organism that share a developmental origin. This approach can be particularly informative in animals with repetitive body segments, such as centipedes.

RESULTS

Here, we investigate morphological and biochemical aspects of the defensive telopodal glandular organs borne on the posterior legs of venomous stone centipedes (Lithobiomorpha), using a multimethod approach, including behavioural observations, comparative morphology, proteomics, comparative transcriptomics and molecular phylogenetics. We show that the anterior venom system and posterior telopodal defence system are functionally convergent serial homologues, where one (telopodal defence) represents a model for the putative early evolutionary state of the other (venom). Venom glands and telopodal glandular organs appear to have evolved from the same type of epidermal gland (four-cell recto-canal type) and while the telopodal defensive secretion shares a great degree of compositional overlap with centipede venoms in general, these similarities arose predominantly through convergent recruitment of distantly related toxin-like components. Both systems are composed of elements predisposed to functional innovation across levels of biological complexity that range from proteins to glands, demonstrating clear parallels between molecular and morphological traits in the properties that facilitate the evolution of novelty.

CONCLUSIONS

The evolution of the lithobiomorph telopodal defence system provides indirect empirical support for the plausibility of the hypothesised evolutionary origin of the centipede venom system, which occurred through functional innovation and gradual specialisation of existing epidermal glands. Our results thus exemplify how continuous transformation and functional innovation can drive the apparent discontinuous emergence of novelties on higher levels of biological complexity.

The Internal Structure of the Velvet Worm Projectile Slime: A Small-Angle Scattering Study

For prey capture and defense, velvet worms eject an adhesive slime which has been established as a model system for recyclable complex liquids. Triggered by mechanical agitation, the liquid bio-adhesive rapidly transitions into solid fibers. In order to understand this mechanoresponsive behavior, here, the nanostructural organization of slime components are studied using small-angle scattering with neutrons and X-rays. The scattering intensities are successfully described with a three-component model accounting for proteins of two dominant molecular weight fractions and nanoscale globules. In contrast to the previous assumption that high molecular weight proteins-the presumed building blocks of the fiber core-are contained in the nanoglobules, it is found that the majority of slime proteins exist freely in solution. Only less than 10% of the slime proteins are contained in the nanoglobules, necessitating a reassessment of their function in fiber formation. Comparing scattering data of slime re-hydrated with light and heavy water reveals that the majority of lipids in slime are contained in the nanoglobules with homogeneous distribution. Vibrating mechanical impact under exclusion of air neither leads to formation of fibers nor alters the bulk structure of slime significantly, suggesting that interfacial phenomena and directional shearing are required for fiber formation.

Biological Materials Processing: Time-Tested Tricks for Sustainable Fiber Fabrication

There is an urgent need to improve the sustainability of the materials we produce and use. Here, we explore what humans can learn from nature about how to sustainably fabricate polymeric fibers with excellent material properties by reviewing the physical and chemical aspects of materials processing distilled from diverse model systems, including spider silk, mussel byssus, velvet worm slime, hagfish slime, and mistletoe viscin. We identify common and divergent strategies, highlighting the potential for bioinspired design and technology transfer. Despite the diversity of the biopolymeric fibers surveyed, we identify several common strategies across multiple systems, including: (1) use of stimuli-responsive biomolecular building blocks, (2) use of concentrated fluid precursor phases (e.g., coacervates and liquid crystals) stored under controlled chemical conditions, and (3) use of chemical (pH, salt concentration, redox chemistry) and physical (mechanical shear, extensional flow) stimuli to trigger the transition from fluid precursor to solid material. Importantly, because these materials largely form and function outside of the body of the organisms, these principles can more easily be transferred for bioinspired design in synthetic systems. We end the review by discussing ongoing efforts and challenges to mimic biological model systems, with a particular focus on artificial spider silks and mussel-inspired materials.

Complete Sequences of the Velvet Worm Slime Proteins Reveal that Slime Formation is Enabled by Disulfide Bonds and Intrinsically Disordered Regions

The slime of velvet worms (Onychophora) is a strong and fully biodegradable protein material, which upon ejection undergoes a fast liquid-to-solid transition to ensnare prey. However, the molecular mechanisms of slime self-assembly are still not well understood, notably because the primary structures of slime proteins are yet unknown. Combining transcriptomic and proteomic studies, the authors have obtained the complete primary sequences of slime proteins and identified key features for slime self-assembly. The high molecular weight slime proteins contain cysteine residues at the N- and C-termini that mediate the formation of multi-protein complexes via disulfide bonding. Low complexity domains in the N-termini are also identified and their propensity for liquid-liquid phase separation is established, which may play a central role in slime biofabrication. Using solid-state nuclear magnetic resonance, rigid and flexible domains of the slime proteins are mapped to specific peptide domains. The complete sequencing of major slime proteins is an important step toward sustainable fabrication of polymers inspired by the velvet worm slime.

The Ties that Stick: Challenges and future promise in the field of bioadhesives

Bioadhesives are wet or dry polymeric compounds that rely upon physical and chemical properties to generate characteristic sticky forces. The past decade has seen a rapidly evolving field of research around the functions, genetics, biochemistry, and mimetics of bioadhesives, but challenges unique to this research area continue to arise. We polled the presenters of SICB Symposium #8 to describe the "Ties that Stick:" challenges and exciting prospects that most resonated with their research pursuits. Themes that emerged from the poll included difficulties working with adhesive-producing organisms, field inherent knowledge gaps in theoretical modeling, molecular interactions, technology, and the interdisciplinary rigor of the bioadhesives field. We address each challenge with a discussion of the opportunities and applications presented by bioadhesives research.

Complex fluids in animal survival strategies

Animals have evolved distinctive survival strategies in response to constant selective pressure. In this review, we highlight how animals exploit flow phenomena by manipulating their habitat (exogenous) or by secreting (endogenous) complex fluids. Ubiquitous endogenous complex fluids such as mucus demonstrate rheological versatility and are therefore involved in many animal behavioral traits ranging from sexual reproduction to protection against predators. Exogenous complex fluids such as sand can be used either for movement or for predation. In all cases, time-dependent rheological properties of complex fluids are decisive for the fate of the biological behavior and vice versa. To exploit these rheological properties, it is essential that the animal is able to sense the rheology of their surrounding complex fluids in a timely fashion. As timing is key in nature, such rheological materials often have clearly defined action windows matching the time frame of their direct biological behavior. As many rheological properties of these biological materials remain poorly studied, we demonstrate with this review that rheology and material science might provide an interesting quantitative approach to study these biological materials in particular in context towards ethology and bio-mimicking material design.

Adaptation and Evolution of Biological Materials

Research into biological materials often centers on the impressive material properties produced in Nature. In the process, however, this research often neglects the ecologies of the materials, the organismal contexts relating to how a biological material is actually used. In biology, materials are vital to organismal interactions with their environment and their physiology, and also provide records of their phylogenetic relationships and the selective pressures that drive biological novelties. With the papers in this symposium, we provide a view on cutting-edge work in biological materials science. The collected research delivers new perspectives on fundamental materials concepts, offering surprising insights into biological innovations and challenging the boundaries of materials’ characterization techniques. The topics, systems, and disciplines covered offer a glimpse into the wide range of contemporary biological materials work. They also demonstrate the need for progressive “whole organism thinking” when characterizing biological materials, and the importance of framing biological materials research in relevant, biological contexts.