Cephalopod-inspired camouflage
Adaptive camouflage array in a flexible, bent configuration.
Mimicking the rapid, complex, adaptive camouflage systems of cuttlefish, octopus, and squid presents various technical challenges. Cunjiang Yu et al. (pp. 12998–13003) constructed an adaptive camouflage system inspired by the cellular mechanisms known to enable camouflage in cephalopods. The top layer of the artificial system is composed of a temperature-sensitive dye that appears black and opaque at low temperatures and clear at temperatures above 47 °C, mimicking the cephalopod chromatophore that expands and contracts to produce color. A layer of silver below the dye provides a white reflective surface, and an ultrathin silicon diode below the silver modulates the dye’s temperature and mimics natural muscle actuation. A base layer contains distributed, multiplexed photodetectors that offer functionality similar to the photosensitive opsin proteins in cephalopod cells. Arranged into a flexible array of unit cells, the adaptive camouflage system responds to various changing patterns of illumination within 1–2 seconds, without user input. The findings may lead to fully tunable, full-spectrum adaptive camouflage integrated into scalable, large-area electronics with commercial, military, and industrial applications, according to the authors. — P.G.
Quantifying poaching’s contribution to elephant declines
Male African elephant that was poached. Image courtesy of David Daballen (Save the Elephants, Nairobi).
The covert nature of illegal elephant killings have precluded attempts to quantify the contribution of poaching to population declines. To develop repeatable, data-based estimates of elephant poaching rates, George Wittemyer et al. (pp. 13117–13121) examined demographic data and analyzed cause of death for African elephant populations. To investigate elephant poaching rates at a local scale, the authors surveyed elephant carcasses in Kenya’s Samburu National Reserve to distinguish between illegal and natural sources of mortality. Locally, poaching rates increased with increases in the local market price for ivory and seizures of illegally harvested ivory throughout Kenya and the world. To estimate poaching at a continental scale, the authors extended their initial analysis by combining demographic data for the species with carcass survey data covering African elephant populations at 45 sites across Africa. At the continental scale, African elephant populations suffered illegal killing rates of approximately 7% each year from 2010 to 2012, and preliminary data from 2013 indicated a killing rate higher than 5%. According to the authors, illegal elephant killings drive annual declines in populations of 2%, a rate that is unsustainable for the species’ survival, yet the accurate estimate of population dynamics driven by poaching may help inform conservation measures and management actions. — J.P.J.
Mapping drug routes into a channel’s pore
The binding of local anesthetic benzocaine (pink) to the bacterial sodium channel NavAb via two distinct pathways.
Voltage-gated sodium (Nav) channels control neuronal signaling and are targets for several therapeutic drugs. The structures of several bacterial Nav channels have been solved, enabling investigations of channel–drug interactions. Céline Boiteux et al. (pp. 13057–13062) used the Anton supercomputer to simulate the interaction of the bacterial NavAb channel with two molecules: the local anesthetic benzocaine and the antiepileptic phenytoin. By sampling channel–drug interactions on a multimicrosecond time scale, the authors mapped the trajectory of drug entry and binding to the channel protein. Benzocaine entered the channel via two distinct routes, either slipping between adjacent transmembrane helices and through a fenestration or passing through the closed intracellular gate. The authors characterized seven binding sites for benzocaine on NavAb. At the highest affinity site, where benzocaine binding blocked the pore, the drug interacted with an amino acid residue called phenylalanine via aromatic ring stacking. A similar interaction with a conserved phenylalanine is observed in mammalian Nav channels. Phenytoin bound with high affinity outside the pore at sites that may control channel function, but failed to cross the closed gate. According to the authors, the identification of low-affinity sites and pathways of drug access suggests potential targets for Nav channel inhibition. — C.B.
Pathogenic pathway of type 2 diabetes
Mice lacking glucagon receptors on a high fat diet with insulin therapy (Left) and without (Right).
Type 2 diabetes (T2D) poses an increasing threat to health worldwide, but its underlying pathogenesis remains unclear. Patients with this genetic, diet-induced disease fail to respond to insulin, exhibiting elevated levels of insulin and blood glucose. Young Lee et al. (pp. 13217–13222) developed a rodent model of high fat diet-induced T2D lacking the action of glucagon, a hormone normally suppressed and opposed by insulin. The authors report that the obese, leptin receptor-defective rodents failed to develop hyperglycemia unless glucagon action was restored or the animals were administered high concentrations of insulin. The findings suggest that the unopposed glucagon action in T2D is necessary to support elevated blood glucose of diabetes. The authors conclude that glucagon plays two essential pathogenic roles in diet-induced T2D: maintaining a rate of hepatic glucose production that exceeds the rate of glucose clearance, and enabling diet-induced hyperinsulinemia. According to the authors, the findings suggest that suppressing glucagon or its action may benefit individuals with T2D. — A.G.
Bacterial defense against neutrophils
Neutrophils serve as one of the body’s lines of defense against infection, neutralizing pathogens via phagocytosis, secretion of antimicrobial compounds, or the formation of extracellular traps, and central to these mechanisms are neutrophil serine protease enzymes (NSP). Daphne Stapels et al. (pp. 13187–13192) investigated whether a common human bacterial pathogen and target of NSPs, Staphylococcus aureus, has evolved defenses against the actions of NSPs. The authors incubated S. aureus culture medium with an NSP in vitro and observed that S. aureus secretions contained a family of extracellular adherence proteins (Eap) that inhibited the NSP. X-ray crystallography of the interactions between Eap molecules and NSPs revealed that Eap molecules block the active sites of NSP enzymes. According to the authors, the results suggest a possible mechanism to treat conditions in which an overproduction of NSPs causes inflammation. In experiments in mice, the authors also found that S. aureus mutants that were unable to produce Eap proteins produced a weaker infection in the mice than did an S. aureus wild-type strain that produces multiple Eap proteins, suggesting that Eap production influences S. aureus pathogenicity. — J.P.J.
Trophy hunting and evolutionary selection in bighorn sheep
Bighorn sheep. Image courtesy of Wikimedia Commons/Philipp Haupt (Zug, Switzerland).
Trophy hunters, who target animals with coveted traits such as large bodies or horns, are thought to impose a form of artificial selection among bighorn sheep (Ovis canadensis) in Ram Mountain, Alberta, Canada, applying evolutionary pressure that disfavors rams with large horns, such as the prized 4/5 degree curled horn. Because the horn size of bighorn rams has steadily diminished in recent years in trophy-hunted swaths of Alberta and British Columbia, Lochran Traill et al. (pp. 13223–13228) attempted to discern whether hunting has indeed triggered an evolutionary response. Using body mass data collected since 1975 for most of the Ram Mountain bighorn population and a modeling method based on statistical relationships between quantitative trait inheritance and population survival and fecundity, the authors simulated selective hunting and found that body mass, a trait strongly linked to horn size in bighorn sheep, is weakly inherited among bighorns and that hunting likely removes heavy male rams from successive generations. Because evolution acts only on traits bequeathed to descendants, the authors suggest that trophy hunting likely does not result in a strong evolutionary response influencing bighorn body mass and, by association, horn size. According to the authors, the modeling approach might be widely applicable in conservation-related decision-making. — P.N.