A representation of the individual quantum trajectories that connect two points in quantum state space. Classical systems are unmoved when a measurement is performed. Not so quantum systems, where continuous monitoring can direct the quantum state along a random path. Steve Weber et al. have tracked the quantum trajectories in a qubit, consisting of two aluminum paddles connected by a tunable Josephson junction deposited on silicon. The authors manage to determine which of the possible paths between an initial and a final quantum state is the most probable and show that these optimal paths are in agreement with the route predicted by theory, a quantum relative of the principle of least action that defines the correct path linking two points in space and time in classical mechanics. As well as giving insights into the interplay between measurement dynamics and evolution of a system, this work opens up new possibilities for first-principles synthesis of control sequences for complex quantum systems and in information processing. (Cover: Kater Murch)

Antarctic fur seals (Arctocephalus gazella) on an iceberg at Bird Island, South Georgia. This species was hunted almost to extinction by the early twentieth century but numbers began to recover when sealing operations stopped, and thanks to an abundant food supply it has survived in large numbers. But fur seals are particularly vulnerable to climate change as they inhabit a region with fast-changing temperatures, and their relatively long generation time limits their ability to adapt evolutionarily. An analysis of three decades of data from South Georgia now shows that the seals are in decline again, with female numbers down by some 30% between 2003 and 2012. Harsh conditions have, however, selected for higher genetic heterozygosity among females. While this is not in itself an evolutionary response, as environmental conditions continue to worsen, heterozygote advantage could help maintain genetic variation, potentially buying time to allow the species to respond via adaptation. Cover photo: Jaume Forcada

The interior of the target chamber at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California � the object entering from the right is the target positioner, on which a centimetre-scale target is mounted. Knowledge of the behaviour of matter under conditions of extreme pressure is essential for describing the interior state of giant planets such as Jupiter and many extrasolar planets. The NIF is pursuing laboratory astrophysics with shock-free dynamic (ramp) compression up to 50 million atmospheres pressure. Working with the NIF at temperatures below those used in fusion experiments, Raymond Smith and colleagues have achieved a new experimental benchmark in the replication of conditions deep within giant planets. They describe properties of carbon compressed to an unprecedented density of 12 g cm−3. These results also provide some of the most direct experimental tests of quantum-statistical theories developed in the early days of quantum mechanics. [Cover: LLNL]

The fungal pathogen Batrachochytrium dendrobatidis, or Bd, has been implicated in the declines of many amphibian species worldwide. There has been little evidence that amphibians can acquire resistance to this pathogen, but now Jason Rohr and colleagues present experiments on several amphibian species, including the Cuban tree frog Osteopilus septentrionalis, shown here, that demonstrate that frogs can learn to avoid the pathogen, can overcome Bd-induced immunosuppression after repeated exposure, and can be immunized against it using dead pathogen. Conservation projects have removed threatened amphibian species from Bd-positive habitats and are breeding them in captivity. Using vaccines to induce resistance in captive-bred amphibians prior to a return to the wild could make it possible in the future to repopulate areas that have seen catastrophic declines. Cover photo: Joseph Gamble

The discovery of numerous feathered dinosaurs and early birds has set the iconic ‘Urvogel’ (or ‘first bird’) Archaeopteryx in a broader context. But this venerable taxon still has the capacity to surprise. A newly discovered specimen from the Solnhofen limestone in Bavaria - only the eleventh since 1861 - shows a generous covering of feathers all over the body. Of particular note is a hindlimb covering resembling feathered ‘trousers’. Analysis of feather distribution on the limbs and tail strongly suggests that pennaceous feathers - the type we are familiar with on birds today — evolved for reasons other than flight, perhaps for display. Cover photo: Helmut Tischlinger.