Consequences of an amphibian malformity for development and fitness in complex environments

1. Environmental stressors have both lethal and sublethal effects, such as altered developmental rates and the induction of malformations. Ecological interactions, including predation and competition, often amplify such effects, for instance by inducing behavioural changes that increase susceptibility to the stress. 2. Using experimental mesocosms, we asked whether the density of conspecific competitors and predation risk from larval water beetles (Dytiscus spp.) affect the development of malformations in tadpoles of the wood frog (Rana sylvatica). We also examined whether such malformities increase the susceptibility of tadpoles to predation. 3. The risk of predation decreased the frequency of malformities in both low‐ and high‐density treatments, although this effect was greater at low density. Behavioural observations suggested that reductions in activity by amphibian larvae induced by predators mediated these responses by decreasing cumulative exposure to ultraviolet‐B radiation, the putative stressor causing the observed malformity. These results suggest that predators can reduce negative impacts of stressors by inducing behavioural changes in prey organisms. 4. Malformed individuals were twice as vulnerable to predators as non‐malformed individuals, suggesting that sublethal effects can ultimately cause increased mortality.     

Lower-limb joint work and power are modulated during load carriage based on load configuration and walking speed

Soldiers regularly transport loads weighing >20 kg at slow speeds for long durations. These tasks elicit high energetic costs through increased positive work generated by knee and ankle muscles, which may increase risk of muscular fatigue and decrease combat readiness. This study aimed to determine how modifying where load is borne changes lower-limb joint mechanical work production, and if load magnitude and/or walking speed also affect work production. Twenty Australian soldiers participated, donning a total of 12 body armor variations: six different body armor systems (one standard-issue, two commercially available [cARM1-2], and three prototypes [pARM1-3]), each worn with two different load magnitudes (15 and 30 kg). For each armor variation, participants completed treadmill walking at two speeds (1.51 and 1.83 m/s). Three-dimensional motion capture and force plate data were acquired and used to estimate joint angles and moments from inverse kinematics and dynamics, respectively. Subsequently, hip, knee, and ankle joint work and power were computed and compared between armor types and walking speeds. Positive joint work over the stance phase significantly increased with walking speed and carried load, accompanied by 2.3–2.6% shifts in total positive work production from the ankle to the hip (p < 0.05). Compared to using cARM1 with 15 kg carried load, carrying 30 kg resulted in significantly greater hip contribution to total lower-limb positive work, while knee and ankle work decreased. Substantial increases in hip joint contributions to total lower-limb positive work that occur with increases in walking speed and load magnitude highlight the importance of hip musculature to load carriage walking.     

Testing predictions from flight mechanical theory: a case study of Cory’s shearwater and Audouin’s gull

Predictions from flight mechanical theory concerning optimal flight speeds were tested in the field in two Mediterranean seabirds, the Cory’s shearwater Calonectris diomedea and the Audouin’s gull Larus audouinii. Both species were commuting off the coast of Isola di San Pietro, 6 km south-west of the coast of Sardinia. Heading and airspeed were obtained by vector calculation of flight tracks and measured wind. The Cory’s shearwater used a mixture of gliding and active flight. At low wind speeds the proportion of active flight was large but it decreased with increasing wind speed. The mean airspeed was 12.0 m s^–1, which is not significantly different from minimum power speed (V _mp) in active flight or the speed for best glide (V _bg) used in gliding flight. However, the shearwaters showed a significant response to wind increment/decrement, indicating that they were not flying at V _mp, which should be unaffected by head and tailwind. Furthermore, shearwaters can potentially reduce induced drag by the ground effect while flying close to the sea surface at weak winds, which leads to a reduction in characteristic flight speed. We suspect that the predictions for gliding flight are most valid for shearwaters at moderate to high wind speeds, when they should be maximising distance by using V _bg. Audouin’s gulls used active flight exclusively, with a mean airspeed of 11.3 m s^–1 that was significantly different from the predicted V _mp. Interestingly, though, the gulls did not show any significant wind response, indicating that they were flying close to their true V _mp when foraging along the coast. Received: 17 May 2000 / Received in revised form: 21 November 2000 / Accepted: 8 January 2001     

Changes in the Constitution of Thylakoid Membranes in Spruce Needles During an Open-top Chamber Experiment

The goal of the presented paper was to study the emission effects of natural air pollutants on the protein complexes of the thylakoid membrane. The tests were carried out in the frame of a long-term experiment in which spruce trees kept in open-top chambers with unfiltered ambient-air were compared to spruce trees in chambers with purified-air. The reaction centres of photosystem I (P-700), cytochrome f, cytochrome b-563, cytochrome b-559, as well as the oxidation speed of the antennae chlorophylls were quantified. The concentrations of the cytochromes f and b-563 indicate a marked annual rhythm with decreased concentrations during the summer months. The spruce trees in chambers with ambient-air showed a smaller amount of the studied redox components in relation to 1000 molecules of chlorophyll than did the spruce trees in chambers exposed to purified-air. In addition, increased oxidation speed of antennae chlorophylls could be observed on the isolated thylakoid membranes of the spruce trees in chambers with ambient-air conditions. A relationship between the oxidation speed and the ozone concentration of the ambient air could be observed, i.e. with increasing ozone levels the oxidation of the antennae chlorophylls accelerated. However, the damage occurred only with a temporary delay (the so-called memory effect). In case of the cytochromes f and b-563 (components of the cytochrome b₆f-complex), a chamber effect related to changed light conditions became obvious when comparing spruce trees kept in chambers to trees left in their natural surrounding. The reduced photosynthetically active radiation — it is reduced in the chambers by 10 ? 30% — led to a decrease of both cytochromes. In spite of the effects due to the chambers, the results indicate that ozone could be an effective damage factor and this will be of importance with regard to the situation in the low mountain range of Germany.