Multistage Reversible Tg Photomodulation and Hardening of Hydrazone-Containing Polymers.

The glass transition temperature (Tg) of a series of polyacrylate- and polymethacrylate-based polymers having bistable hydrazone photoswitches as pendants increases upon photoisomerization. The ensuing photohardening of the polymeric network was corroborated using nanoindentation measurements. The bistability of the switch allowed us to lock-in and sustain multiple Tg values in the same polymeric material as a function of the hydrazone switch's Z/E isomer ratio, even at elevated temperatures.

New molecular switch architectures.

In this paper we elaborate on recently developed molecular switch architectures and how these new systems can help with the realization of new functions and advancement of artificial molecular machines. Progress in chemically and photoinduced switches and motors is summarized and contextualized such that the reader may gain an appreciation for the novel tools that have come about in the past decade. Many of these systems offer distinct advantages over commonly employed switches, including improved fidelity, addressability, and robustness. Thus, this paper serves as a jumping-off point for researchers seeking new switching motifs for specific applications, or ones that address the limitations of presently available systems.

Shared and unique morphological responses of stream fishes to anthropogenic habitat alteration.

Understanding population-level responses to novel selective pressures can elucidate evolutionary consequences of human-altered habitats. Stream impoundments (reservoirs) alter riverine ecosystems worldwide, exposing stream fishes to uncommon selective pressures. Assessing phenotypic trait divergence in reservoir habitats will be a first step in identifying the potential evolutionary and ecological consequences of stream impoundments. We tested for body shape divergence in four stream-adapted fishes found in both habitats within three separate basins. Shape variation among fishes was partitioned into shared (exhibited by all species) and unique (species-specific) responses to reservoir habitats. All fishes demonstrated consistent significant shared and unique morphological responses to reservoir habitats. Shared responses were linked to fin positioning, decreased body depths and larger caudal areas; traits likely related to locomotion. Unique responses were linked to head shape, suggesting species-specific responses to abiotic conditions or changes to their trophic ecology in reservoirs. Our results highlight how human-altered habitats can simultaneously drive similar and unique trait divergence in native populations.

Cobweb-weaving spiders produce different attachment discs for locomotion and prey capture.

Spiders' cobwebs ensnare both walking and flying prey. While the scaffolding silk can entangle flying insects, gumfoot silk threads pull walking prey off the ground and into the web. Therefore, scaffolding silk needs to withstand the impact of the prey, whereas gumfoot silk needs to easily detach from the substrate when contacted by prey. Here we show that spiders accomplish these divergent demands by creating attachment discs of two distinct architectures using the same pyriform silk. A 'staple-pin' architecture firmly attaches the scaffolding silk to the substrate and a previously unknown 'dendritic' architecture weakly attaches the gumfoot silk to the substrate. Gumfoot discs adhere weakly, triggering a spring-loaded trap, while the strong adhesion of scaffolding discs compels the scaffolding threads to break instead of detaching. We describe the differences in adhesion for these two architectures using tape-peeling models and design synthetic attachments that reveal important design principles for controlled adhesion.