Latitudinal, sex and inter-specific differences in mercury and other trace metal concentrations in Adélie and Emperor penguins in the Ross Sea, Antarctica.

We sought to determine mercury (Hg) and other trace metal concentrations in Adélie (Pygoscelis adeliae) and emperor penguin (Aptenodytes forsteri) breast feathers from the Ross Sea, Antarctica, and relate those concentrations to the trophic position and the habitats in which each of these species forage. Adélie penguin feathers from the southern Ross Sea colonies were higher in Hg than those sampled further north in the Ross Sea, potentially due to greater exposure to local sources, such as volcanism. Female Adélie penguins had lower feather total Hg concentrations than males. This may reflect female penguin's capacity to eliminate Hg through the egg development and laying process, or the larger and/or older prey items that male birds can consume, reflected by their higher trophic position. Emperor penguins have higher Hg concentrations than Adélie penguins which is also partially explained by Adélie penguins feeding at lower trophic levels than emperor penguins.

Flying south: Foraging locations of the Hutton's shearwater (Puffinus huttoni) revealed by Time-Depth Recorders and GPS tracking.

The Hutton's shearwater Puffinus huttoni is an endangered seabird endemic to Kaikoura, New Zealand, but the spatial and temporal aspects of its at-sea foraging behavior are not well known.To identify foraging areas and estimate trip durations, we deployed Global Positioning Systems (GPS) devices and Time-Depth Recorders (TDR) on 26 adult Hutton's shearwaters during the chick-rearing period in 2017 and 2018.We found Hutton's shearwaters traveled much further from their breeding grounds at Kaikoura than previously considered, with most individuals foraging in coastal and oceanic areas 125-365 km south and near Banks Peninsula. Trip durations varied from 1 to 15 days (mean = 5 days), and total track lengths varied from 264 to 2,157 km (mean = 1092.9 km).Although some diving occurred in near-shore waters near the breeding colony, most foraging was concentrated in four regions south of Kaikoura. Dive durations averaged 23.2 s (range 8.1 to 71.3 s) and dive depths averaged 7.1 m (range 1.5 to 30 m). Foraging locations had higher chlorophyll a levels and shallower water depths than nonforaging locations. Birds did not feed at night, but tended to raft in areas with deeper water than foraging locations.Mapping the spatial and temporal distribution of Hutton's shearwaters at sea will be fundamental to their conservation, as it can reveal potential areas of overlap with fisheries and other industrial users of the marine environment.

Juvenile Osprey Navigation during Trans-Oceanic Migration.

To compensate for drift, an animal migrating through air or sea must be able to navigate. Although some species of bird, fish, insect, mammal, and reptile are capable of drift compensation, our understanding of the spatial reference frame, and associated coordinate space, in which these navigational behaviors occur remains limited. Using high resolution satellite-monitored GPS track data, we show that juvenile ospreys (Pandion haliaetus) are capable of non-stop constant course movements over open ocean spanning distances in excess of 1500 km despite the perturbing effects of winds and the lack of obvious landmarks. These results are best explained by extreme navigational precision in an exogenous spatio-temporal reference frame, such as positional orientation relative to Earth's magnetic field and pacing relative to an exogenous mechanism of keeping time. Given the age (<1 year-old) of these birds and knowledge of their hatching site locations, we were able to transform Enhanced Magnetic Model coordinate locations such that the origin of the magnetic coordinate space corresponded with each bird's nest. Our analyses show that trans-oceanic juvenile osprey movements are consistent with bicoordinate positional orientation in transformed magnetic coordinate or geographic space. Through integration of movement and meteorological data, we propose a new theoretical framework, chord and clock navigation, capable of explaining the precise spatial orientation and temporal pacing performed by juvenile ospreys during their long-distance migrations over open ocean.

Respiratory flexibility and efficiency are affected by simulated global change in Arctic plants.

Laboratory studies indicate that, in response to environmental conditions, plants modulate respiratory electron partitioning between the 'energy-wasteful' alternative pathway (AP) and the 'energy-conserving' cytochrome pathway (CP). Field data, however, are scarce. Here we investigate how 20-yr field manipulations simulating global change affected electron partitioning in Alaskan Arctic tundra species. We sampled leaves from three dominant tundra species - Betula nana, Eriophorum vaginatum and Rubus chamaemorus - that had been strongly affected by manipulations of soil nutrients, light availability, and warming. We measured foliar dark respiration, in-vivo electron partitioning and alternative oxidase/cytochrome c oxidase concentrations in addition to leaf traits and mitochondrial ultrastructure. Changes in leaf traits and ultrastructure were similar across species. Respiration at 20°C (R(20)) was reduced 15% in all three species grown at elevated temperature, suggesting thermal acclimation of respiration. In Betula, the species with the largest growth response to added nutrients, CP activity increased from 9.4 ± 0.8 to 16.6 ± 1.6 nmol O(2) g(-1) DM s(-1) whereas AP activity was unchanged. The ability of Betula to selectively increase CP activity in response to the environment may contribute to its overall ecological success by increasing respiratory energy efficiency, and thus retaining more carbon for growth.

Modulation of respiratory metabolism in response to nutrient changes along a soil chronosequence.

Laboratory studies indicate that plant respiratory efficiency may decrease in response to low nutrient availability due to increased partitioning of electrons to the energy-wasteful alternative oxidase (AOX); however, field confirmation of this hypothesis is lacking. We therefore investigated plant respiratory changes associated with succession and retrogression in soils aged from 10 to 120 000 years along the Franz Josef soil chronosequence, New Zealand. Respiration rates and electron partitioning were determined based on oxygen isotopic fractionation. Leaf structural traits, foliar nutrient status, carbohydrates and species composition were measured as explanatory variables. Although soil nutrient levels and species composition varied by site along the chronosequence, foliar respiration across all sites and species corresponded strongly with leaf nitrogen concentration (r(2) = 0.8). In contrast, electron partitioning declined with increasing nitrogen/phosphorus (r(2) = 0.23) and AOX activity correlated with phosphorus (r(2) = 0.64). Independently, total respiration was further associated with foliar Cu, possibly linked to its effect on AOX. Independent control of AOX and cytochrome pathway activities is also discussed. These responses of plant terminal respiratory oxidases - and therefore respiratory carbon efficiency - to multiple nutrient deficiencies demonstrate that modulation of respiratory metabolism may play an important role in plant responses to nutrient gradients.

A field-compatible method for measuring alternative respiratory pathway activities in vivo using stable O2 isotopes.

Plants can alter rates of electron transport through the alternative oxidase (AOX) pathway in response to environmental cues, thus modulating respiratory efficiency, but the (18)O discrimination method necessary for measuring electron partitioning in vivo has been restricted to laboratory settings. To overcome this limitation, we developed a field-compatible analytical method. Series of plant tissue subsamples were incubated in 12 mL septum-capped vials for 0.5-4 h before aliquots of incubation air were injected into 3.7 mL evacuated storage vials. Vials were stored for up to 10 months before analysis by mass spectrometry. Measurements were corrected for unavoidable contamination. Additional mathematical tools were developed for detecting and addressing non-linearity (whether intrinsic or due to contamination) in the data used to estimate discrimination values. Initial contamination in the storage vials was 0.03 ± 0.01 atm; storing the gas samples at -17 °C eliminated further contamination effects over 10 months. Discrimination values obtained using our offline incubation and computation method replicated previously reported results over a range of 10-31‰, with precision generally better than ±0.5‰. Our method enables large-scale investigations of plant alternative respiration along natural environmental gradients under field conditions.

Correcting for nonlinearity effects of continuous flow isotope ratio mass spectrometry across a wide dynamic range.

RATIONALE: Environmental and biological investigations may require samples that vary over a wide range of concentrations and isotope ratios, making measurements using continuous flow isotope ratio mass spectrometry (CF-IRMS) problematic due to nonlinear signal response. We therefore developed a mathematical approach for correcting nonlinearities over a wide range of sample concentrations and actual δ values. METHODS: Dilution series for two standards were prepared in septum-capped vials and introduced into the mass spectrometer via the standard sampling pathway. Parameters for a nonlinear signal correction were determined by regression on measured isotope ratio vs. both signal strength and actual isotope ratio. We further extended the dynamic range by adjusting the position of an open split based on analyte concentration. Effects of the open split setting required additional mathematical correction. RESULTS: The nonlinearities were corrected over a 100-fold range of sample concentrations and across a 600‰ change in isotope ratios (for δO(2) /N(2) values). The precision, measured as standard deviation, across the upper 90% of the concentration range was ±0.08‰, ±0.05‰, and ±2.6‰ for δ(18) O, δ(15) N, and δO(2) /N(2) values, respectively; the precision across the lower 10% of the range was ±0.22‰, ±0.07‰, and ±7.6‰, respectively. In all cases the linearity correction represented only a small fraction of these precision values. CONCLUSIONS: The empirical correction described here provides a relatively simple yet effective way to increase the usable signal range for CF-IRMS applications. This improvement in dynamic range should be especially helpful for environmental and biological field studies, where sampling methods may be constrained by external factors.

Straight as an arrow: humpback whales swim constant course tracks during long-distance migration.

Humpback whale seasonal migrations, spanning greater than 6500 km of open ocean, demonstrate remarkable navigational precision despite following spatially and temporally distinct migration routes. Satellite-monitored radio tag-derived humpback whale migration tracks in both the South Atlantic and South Pacific include constant course segments of greater than 200 km, each spanning several days of continuous movement. The whales studied here maintain these directed movements, often with better than 1° precision, despite the effects of variable sea-surface currents. Such remarkable directional precision is difficult to explain by established models of directional orientation, suggesting that alternative compass mechanisms should be explored.