Genome evolution: groping in the soil interstices

Parallel decay of vision genes in subterranean water beetles

In the framework of neutral theory of molecular evolution, genes specific to the development and function of eyes in subterranean animals living in permanent darkness are expected to evolve by relaxed selection, ultimately becoming pseudogenes. However, definitive empirical evidence for the role of neutral processes in the loss of vision over evolutionary time remains controversial. In previous studies, we characterized an assemblage of independently-evolved water beetle (Dytiscidae) species from a subterranean archipelago in Western Australia, where parallel vision and eye loss have occurred. Using a combination of transcriptomics and exon capture, we present evidence of parallel coding sequence decay, resulting from the accumulation of frameshift mutations and premature stop codons, in eight phototransduction genes (arrestins, opsins, ninaC and transient receptor potential channel genes) in 32 subterranean species in contrast to surface species, where these genes have open reading frames. Our results provide strong evidence to support neutral evolutionary processes as a major contributing factor to the loss of phototransduction genes in subterranean animals, with the ultimate fate being the irreversible loss of a light detection system.

Soft Three-Dimensional Robots with Hard Two-Dimensional Materials

Inspired by biological organisms, soft engineered robots seek to augment the capabilities of rigid robots by providing safe, compliant, and flexible interfaces for human-machine interactions. Soft robots provide significant advantages in applications ranging from pick-and-place, prostheses, wearables, and surgical and drug-delivery devices. Conventional soft robots are typically composed of elastomers or gels, where changes in material properties such as stiffness or swelling control actuation. However, soft materials have limited electronic and optical performance, mechanical rigidity, and stability against environmental damage. Atomically thin two-dimensional layered materials (2DLMs) such as graphene and transition metal dichalcogenides have excellent electrical, optical, mechanical, and barrier properties and have been used to create ultrathin interconnects, transistors, photovoltaics, photocatalysts, and biosensors. Importantly, although 2DLMs have high in-plane stiffness and rigidity, they have high out-of-plane flexibility and are soft from that point of view. In this Perspective, we discuss the use of 2DLMs either in their continuous monolayer state or as composites with elastomers and hydrogels to create soft three-dimensional (3D) robots, with a focus on origami-inspired approaches. We classify the field, outline major methods, and highlight challenges toward seamless integration of hybrid materials to create multifunctional robots with the characteristics of soft devices.