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. 2017 Sep 8;7(1):11042.
doi: 10.1038/s41598-017-11459-8.

Insight into shark magnetic field perception from empirical observations

James M Anderson  1   2 , Tamrynn M Clegg  3 , Luisa V M V Q Véras  4 , Kim N Holland  3   5
Affiliations

Insight into shark magnetic field perception from empirical observations

James M Anderson et al. Sci Rep. .

Abstract

Elasmobranch fishes are among a broad range of taxa believed to gain positional information and navigate using the earth's magnetic field, yet in sharks, much remains uncertain regarding the sensory receptors and pathways involved, or the exact nature of perceived stimuli. Captive sandbar sharks, Carcharhinus plumbeus were conditioned to respond to presentation of a magnetic stimulus by seeking out a target in anticipation of reward (food). Sharks in the study demonstrated strong responses to magnetic stimuli, making significantly more approaches to the target (p = < 0.01) during stimulus activation (S+) than before or after activation (S-). Sharks exposed to reversible magnetosensory impairment were less capable of discriminating changes to the local magnetic field, with no difference seen in approaches to the target under the S+ and S- conditions (p = 0.375). We provide quantified detection and discrimination thresholds of magnetic stimuli presented, and quantify associated transient electrical artefacts. We show that the likelihood of such artefacts serving as the stimulus for observed behavioural responses was low. These impairment experiments support hypotheses that magnetic field perception in sharks is not solely performed via the electrosensory system, and that putative magnetoreceptor structures may be located in the naso-olfactory capsules of sharks.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Behavioural responses of unimpaired sharks to presented magnetic stimulus. (A) Histogram showing median number of passes over the target for all sharks, in each 1 minute time bin. S+ minute is shaded red, all other 1 minute time bins (S−) are shaded grey. Error bars show standard error. (B) Box & Whisker plot showing mean proportion of passes over the target, per shark, across the series of ten unimpaired trials, mean value is denoted by x. S+ minute is shaded red, all other 1 minute time bins (S−) are shaded grey. Friedman Rank Sum tests were used to determine any differences in time bins. Wilcoxon Signed Rank Tests were used to compare mean proportion of passes over the target, averaged per shark in the eleventh minute time bin with each other one minute time bin. Averaged per shark, a significantly higher proportion of passes over the target was seen in the S+ (11th) minute. *p < 0.01.
Figure 2
Figure 2
Placement of magnets designed to impair magnetic stimulus perception. Neodymium magnets were embedded horizontally in gelatine within a sealed container and aligned with the longitudinal axes of the olfactory organs.
Figure 3
Figure 3
Behavioural responses of sensory impaired sharks to presented magnetic stimulus. (A) Histogram showing median number of passes over the target for all sharks, in each 1 minute time bin. S+ minute is shaded red. Error bars show standard error. (B) Box & Whisker plot showing mean proportion of passes over the target, averaged per shark, across the series of ten sensory-impaired trials, mean value is denoted by x. S+ minute is shaded red, all other 1 minute time bins (S−) are shaded grey. Friedman Rank Sum tests were used to determine any differences in time bins. No difference was found under S+ or S− conditions when animals had undergone magnetic impairment treatment.
Figure 4
Figure 4
Measured profiles of total magnetic intensity. Changes in magnetic field intensity (μT) associated with magnetic stimulus presentation were measured across the diameter of the tank at increments of 3 ft (0.9144 m), from centre (0 m) to periphery (3.5 m) (coil axis is the centre of the tank). Y axis values correspond to magnetic field changes (Δ µT) associated with use of 12 volt and 6 volt power sources. Z axis values correspond to magnetic field changes (δ µT) associated with use of 1.5 volt power source, with 5.6k Ω of resistance built into the circuit. Vertical red line indicates tank periphery.
Figure 5
Figure 5
Electrical field measurements associated with background electrical noise. Electrical field artefacts occurring during presentation of the magnetic stimulus were measured using a Trifield® Natural EM Meter (AlphaLab Inc., Salt Lake City, UT, USA), capable of taking measurements every millisecond. Grey shaded region indicates period of magnetic field activation (S+ minute; 600–660 seconds). N.b. the constant and random fluctuation of background electrical noise in the environment, both before, during and after magnetic field activation. Maximum range of recorded background electrical field oscillation (noise) during the period of stimulus activation was 51 mV, occurring at rate of 1.02 mV/cm/s−1. Peak voltage (maximum “spike” above zero) was 33 mV, or 3.3e nV which occurred 17 seconds after stimulus activation.
Figure 6
Figure 6
Calculated induced voltage gradient associated with magnetic stimulus. Modelled gradients correspond to changes in total magnetic field intensity of 3 μT (red line) and 0.029 μT (blue line) respectively. Red line corresponds to Y axis, blue line corresponds to Z (secondary) axis. Voltage gradients induced by modification of the local magnetic field within the tank were calculated from centre (coil axis – 0 m) to periphery (3.5 m) at increments of 3 ft (0.9144 m). Induced voltages increased linearly with distance, peaking at 73.3 nV cm−1 at the tank periphery when a magnetic field modification of 0.029 µT was applied. Calculated time to reach peak induced voltage gradient following onset of magnetic stimulus was 2.7 milliseconds.
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References

    1. Wiltschko R, Wiltschko W. Magnetoreception. Bioessays. 2006;28.2:157–168. doi: 10.1002/bies.20363. - DOI - PubMed
    1. Mann S, Sparks N, Board R. Magnetotactic bacteria: microbiology, biomineralization, palaeomagnetism and biotechnology. Adv. Microb. Physiol. 1990;31:125–181. doi: 10.1016/S0065-2911(08)60121-6. - DOI - PubMed
    1. Blakemore R. Magnetotactic bacteria. Science. 1975;190:377–379. doi: 10.1126/science.170679. - DOI - PubMed
    1. Torres FF, Botanica D, Paulo S. Magnetite magnetotaxis algae. Biophys. J. 1986;50:375–378. doi: 10.1016/S0006-3495(86)83471-3. - DOI - PMC - PubMed
    1. Brown F, Webb H, Barnwell F. A compass directional phenomenon in mud-snails and its relation to magnetism. Biol. Bull. 1964;127:206–220. doi: 10.2307/1539220. - DOI

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