Journal of Experimental Biology - Latest Issue

• Galápagos marine iguanas reduce metabolism to conserve energy during El Niño

• Falcons can use olfaction to detect food in a test setting

  ABSTRACT

  Falcons, along with many other raptors, have long been considered to have little or no olfactory sense. A controlled experiment in which peregrine falcons, Falco peregrinus peregrinus, and peregrine falcon/gyrfalcon hybrids F. peregrinus×rusticolus used smell to detect their food showed that all the test birds had a sense of smell. The results add to a growing body of evidence that birds, including falcons, do indeed possess and utilise an olfactory sense.

• Marine iguanas have lower metabolic rates during El Niño

  ABSTRACT

  The Galápagos marine iguana (Amblyrhynchus cristatus), the world's only marine lizard, feeds predominantly on algae. Owing to warming waters and reduced upwelling, algal abundance is reduced during El Niño events, causing high iguana mortality. During such periods, adult iguanas may shrink in size, a compelling phenomenon that has been suggested as an adaptation to reduce energetic needs. However, shifts in energy consumption have never been tested directly. We measured the body condition and metabolic rates of marine iguanas during an El Niño year and the subsequent neutral year. During El Niño, body mass relative to length was 17% lower, girth relative to length was 12% lower, and resting metabolic rates were 20% lower. This supports the hypothesis that marine iguanas partly offset the adverse effect of El Niño by an active response aimed at reducing their energy consumption, complementary to the energy-saving effect of body size reduction. Future ocean warming could force this endemic species to resort to such strategies increasingly often, and will likely exacerbate the already-high mortality rates caused by these events.

• The energetics and mechanics of trunk angle during flat and inclined walking in humans

  ABSTRACT

  During flat walking, the trunk typically maintains an upright posture. However, when walking up slopes, humans tend to increase trunk flexion. This behaviour is not easily understood as increasing trunk flexion increases the torque required at the hip joint to stop the trunk from falling forwards. In this study, we investigated how trunk flexion affected metabolic cost and mechanical work during flat and inclined walking. Seven healthy subjects walked on a flat and inclined surface while trunk flexion angle was enforced using visual feedback. We found that healthy individuals tended to walk at the trunk angle that minimizes metabolic cost, and this trunk angle increased with the incline angle of the walking surface. As trunk flexion increased, hip work rate increased whereas knee and ankle work rate decreased. This study suggests that trunk flexion angle is another feature of gait controlled to maintain energetic efficiency by altering joint level mechanics.

• Comparison of ankle dorsiflexion using XROMM and external angular kinematics in a quadrupedally walking macaque

  ABSTRACT

  Movement at complex joints, such as the ankle, can be challenging to quantify from external kinematics alone. We compared X-ray reconstruction of moving morphology (XROMM) and angles derived from high-speed video footage to study dorsiflexion in the ankle of a rhesus macaque (Macaca mulatta) during stance phase. We found inconsistent correspondence between angles measured on standard videos using five approaches and those measured directly on the talocrural joint using XROMM, indicating that different measurement methods capture different kinematic processes. Many externally measured angles indicate a range of motion of 30 deg during stance phase. The XROMM data, however, demonstrate that the talocrural joint itself only dorsiflexes about 15 deg through stance phase, with much greater mobility during swing phase. This suggests that other parts of the foot, likely the midfoot, contribute substantially to dorsiflexion in stance phase, while the talocrural joint is actively held in place.