Clutter resilience via auditory stream segregation in echolocating greater mouse-eared bats.

Bats use echolocation to navigate and hunt in darkness, and must in that process segregate target echoes from unwanted clutter echoes. Bats may do this by approaching a target at steep angles relative to the plane of the background, utilizing their directional transmission and receiving systems to minimize clutter from background objects, but it remains unknown how bats negotiate clutter that cannot be spatially avoided. Here, we tested the hypothesis that when movement no longer offers spatial release, echolocating bats mitigate clutter by calling at lower source levels and longer call intervals to ease auditory streaming. We trained five greater mouse-eared bats (Myotis myotis) to land on a spherical loudspeaker with two microphones attached. We used a phantom-echo setup, where the loudspeaker/target transmitted phantom clutter echoes by playing back the bats' own calls at time delays of 1, 3 and 5 ms with a virtual target strength 7 dB higher than the physical target. We show that the bats successfully landed on the target, irrespective of the clutter echo delays. Rather than decreasing their source levels, the bats used similar source level distributions in clutter and control trials. Similarly, the bats did not increase their call intervals, but instead used the same distribution of call intervals across control and clutter trials. These observations reject our hypothesis, leading us to conclude that bats display great resilience to clutter via short auditory integration times and acute auditory stream segregation rather than via biosonar adjustments.

Whistling is metabolically cheap for communicating bottlenose dolphins (Tursiops truncatus).

Toothed whales depend on sound for communication and foraging, making them potentially vulnerable to acoustic masking from increasing anthropogenic noise. Masking effects may be ameliorated by higher amplitudes or rates of calling, but such acoustic compensation mechanisms may incur energetic costs if sound production is expensive. The costs of whistling in bottlenose dolphins (Tursiops truncatus) have been reported to be much higher (20% of resting metabolic rate, RMR) than theoretical predictions (0.5-1% of RMR). Here, we address this dichotomy by measuring the change in the resting O2 consumption rate (V̇O2 ), a proxy for RMR, in three post-absorptive bottlenose dolphins during whistling and silent trials, concurrent with simultaneous measurement of acoustic output using a calibrated hydrophone array. The experimental protocol consisted of a 2-min baseline period to establish RMR, followed by a 2-min voluntary resting surface apnea, with or without whistling as cued by the trainers, and then a 5-min resting period to measure recovery costs. Daily fluctuations in V̇O2  were accounted for by subtracting the baseline RMR from the recovery costs to estimate the cost of apnea with and without whistles relative to RMR. Analysis of 52 sessions containing 1162 whistles showed that whistling did not increase metabolic cost (P>0.1, +4.2±6.9%) as compared with control trials (-0.5±5.9%; means±s.e.m.). Thus, we reject the hypothesis that whistling is costly for bottlenose dolphins, and conclude that vocal adjustments such as the Lombard response to noise do not represent large direct energetic costs for communicating toothed whales.

Plasma amino acids in Greenlanders and Danes: influence of seasons, residence, ethnicity, and diet.

Basal metabolic rate is elevated among circumpolar populations. It has been our hypotheses that this is reflected in the levels of plasma amino acids, that amino acid concentration in plasma differs between Greenlanders and Danes, and that this difference is related to residence, ethnicity, diet, and season. The purpose of the study was to measure plasma amino acids in Greenlanders and Danes and to analyze the influence of residence, ethnicity, diet, and season. Amino acids in plasma were measured in four groups of healthy subjects both during summer and winter: Group 1, Danes living in Denmark consuming European food; Group 2, Greenlanders living in Denmark consuming European food; Group 3, Greenlanders living in Greenland consuming European food; and Group 4, Greenlanders living in Greenland consuming mainly traditional Greenlandic food. Amino acids were determined by pre-column derivatization with o-phthaldialdehyde and reverse-phase high-performance liquid chromatography with gradient elution and fluorescence detection. Most plasma amino acids were lower during summer than winter in Greenlanders living in Greenland. Comparison of the four groups showed that residence in Greenland was the most important influencing factor for the concentration of plasma amino acids, whereas ethnicity and diet had only a very modest or no effect. These findings could not be attributed to changes in thyroid function. However, the level of physical activity was significantly higher in Groups 3 and 4 than in Groups 1 and 2. Because exercise reduces the amino acid pool in plasma, it is possibly that the higher physical activity among Greenlanders living in Greenland explains the reduction in plasma amino acids during summer. It is concluded that plasma amino acids were lower during summer than winter in Greenlanders living in Greenland compared with Greenlanders in Denmark and Danes. This difference might be due to the higher level of physical activity among Greenlanders in Greenland during the summer period.

Relationship between mercury in blood and 24-h ambulatory blood pressure in Greenlanders and Danes.

BACKGROUND: Intake of mercury with food items from sea mammals and fish has been suggested to be involved in cardiovascular disease, but the relationship between mercury in blood and 24-h ambulatory blood pressure (BP) has never been studied. METHODS: We measured mercury in blood and 24-h BP in four groups of healthy subjects: group 1, Danes living in Denmark consuming European food; group 2, Greenlanders living in Denmark consuming European food; group 3, Greenlanders living in Greenland consuming European food; and group 4, Greenlanders living in Greenland consuming mainly traditional Greenlandic food. RESULTS: Mercury in blood was highest in Greenlanders and increased when they lived in Greenland and consumed traditional Greenlandic food (group 1: 2.2 microg/L (median), group 2: 4.8 microg/L, group 3: 10.8 microg/L, and group 4: 24.9 microg/L). The 24-h BP was the same in all three groups of Greenlanders. However, 24-h diastolic BP was lower among Greenlanders than Danes (71 v 76 mm Hg, P < .000) and 24-h pulse pressure was higher (54 v 50 mm Hg, P < .000). Mercury in blood was significantly and positively correlated to pulse pressure (rho = 0.272, P < .01). CONCLUSIONS: Pulse pressure was higher and diastolic BP was lower in Greenlanders than Danes. Pulse pressure increased with higher mercury content in the blood. Although genetic factors must be responsible to some extent for the difference in pulse pressure between Greenlanders and Danes, the present results seem to support the hypothesis that mercury intake from maritime food is involved in cardiovascular disease.

Ethnic, geographic and dietary influences upon vasoactive hormones and blood pressure among Greenland Inuit and Danes.

AIM: To study levels of vasoactive hormones and urinary excretion of sodium and potassium between groups of Greenland Inuit and Danes, and to analyse the relationship between these hormones and 24-h blood pressure, including nightly blood pressure dips and pulse pressure. METHODS: 145 Greenlandic participants were categorized in three groups according to degree of westernization, based on dietary habits and current place of residence; 41 Danes were included as controls. Twenty-four-hour blood pressure was measured. Venous plasma concentrations of vasoactive hormones were measured. Urine was collected for 24 hours for analysis of excretion of sodium and potassium. RESULTS: The Inuit population of Greenland had a lower diastolic blood pressure, a higher pulse pressure and lower nocturnal blood pressure dip than Danes had. Angiotensin II in plasma and urine excretion of potassium were higher among Greenlanders compared with Danes, irrespective of diet and place of residence. Aldosterone and urine excretion of sodium were significantly higher among participants in Denmark compared with participants in Greenland. Brain natriuretic peptide and atrial natriuretic peptide were independently and negatively associated with diastolic blood pressure, and vasopressin was positively associated with systolic blood pressure and pulse pressure. Ethnic differences in the effect of vasoactive hormones or urinary sodium and potassium excretion could not explain the difference in blood pressure. CONCLUSION: It is suggested that a high dietary intake of potassium and low sodium intake among Greenlanders may affect blood pressure. Further attention should be drawn to the occurrence of high pulse pressure and high activity in the renin-angiotensin system in Inuit populations.