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Learned magnetic map cues and two mechanisms of magnetoreception in turtles

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Kayla Goforth at Texas A&M University
Kayla Goforth
Catherine Lohmann at University of North Carolina at Chapel Hill
Catherine Lohmann
Andrew Gavin
Andrew Gavin
Andrew Gavin
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Reyco Henning
Reyco Henning
Reyco Henning
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Abstract and Figures

Growing evidence indicates that migratory animals exploit the magnetic field of the Earth for navigation, both as a compass to determine direction and as a map to determine geographical position¹. It has long been proposed that, to navigate using a magnetic map, animals must learn the magnetic coordinates of the destination2,3, yet the pivotal hypothesis that animals can learn magnetic signatures of geographical areas has, to our knowledge, yet to be tested. Here we report that an iconic navigating species, the loggerhead turtle (Caretta caretta), can learn such information. When fed repeatedly in magnetic fields replicating those that exist in particular oceanic locations, juvenile turtles learned to distinguish magnetic fields in which they encountered food from magnetic fields that exist elsewhere, an ability that might underlie foraging site fidelity. Conditioned responses in this new magnetic map assay were unaffected by radiofrequency oscillating magnetic fields, a treatment expected to disrupt radical-pair-based chemical magnetoreception4, 5–6, suggesting that the magnetic map sense of the turtle does not rely on this mechanism. By contrast, orientation behaviour that required use of the magnetic compass was disrupted by radiofrequency oscillating magnetic fields. The findings provide evidence that two different mechanisms of magnetoreception underlie the magnetic map and magnetic compass in sea turtles.
Results from conditioning experiments in which turtles learned to discriminate between magnetic fields replicating those that exist near New Hampshire, USA, and in the Gulf of Mexico a, Map showing relative locations of the two treatment fields. The map was created using Natural Earth (https://www.naturalearthdata.com; credit Tom Patterson and Nathaniel Vaughn Kelso). b, In tests conducted immediately after the conditioning period, turtles exhibited significantly higher levels of turtle dance behaviour when experiencing the field in which they had been fed (two-tailed Wilcoxon signed-rank test, w = 123, P = 0.003, Hedge’s g = 0.88, n = 16). See Methods for details of analysis. c, Turtles were tested a second time, 4 months after the initial experiments, without experiencing either the rewarded or unrewarded field in the interim. Turtles still discriminated between the two fields (two-tailed Wilcoxon signed-rank test, w = 118, P = 0.01, Hedge’s g = 0.62, n = 16). Error bars represent s.e.m. To facilitate plotting the large range of responses from individuals, the vertical axis is presented with a square-root transformation to improve visibility of individual data points. Extended Data Fig. 1 shows the same data plotted on a linear scale. Source data
Results from conditioning experiments in which turtles learned to discriminate between magnetic fields replicating those that exist near New Hampshire, USA, and in the Gulf of Mexico a, Map showing relative locations of the two treatment fields. The map was created using Natural Earth (https://www.naturalearthdata.com; credit Tom Patterson and Nathaniel Vaughn Kelso). b, In tests conducted immediately after the conditioning period, turtles exhibited significantly higher levels of turtle dance behaviour when experiencing the field in which they had been fed (two-tailed Wilcoxon signed-rank test, w = 123, P = 0.003, Hedge’s g = 0.88, n = 16). See Methods for details of analysis. c, Turtles were tested a second time, 4 months after the initial experiments, without experiencing either the rewarded or unrewarded field in the interim. Turtles still discriminated between the two fields (two-tailed Wilcoxon signed-rank test, w = 118, P = 0.01, Hedge’s g = 0.62, n = 16). Error bars represent s.e.m. To facilitate plotting the large range of responses from individuals, the vertical axis is presented with a square-root transformation to improve visibility of individual data points. Extended Data Fig. 1 shows the same data plotted on a linear scale. Source data
… 
Results of four additional map assay experiments, in which turtles discriminated between a magnetic field in which they were fed and a magnetic field in which they were not a–d, Turtles differentiated between magnetic fields that exist near: Delaware, USA, and Cuba (a; two-tailed Wilcoxon signed-rank test, w = 108, P = 0.04, Hedge’s g = 0.50, n = 16); Maine and Florida, USA (b; two-tailed Wilcoxon signed-rank test, w = 121, P = 0.004, Hedge’s g = 0.63, n = 16); Newfoundland, Canada and Virginia, USA (c; two-tailed Wilcoxon signed-rank test, w = 115, P = 0.01, Hedge’s g = 0.60, n = 16); and the Turks and Caicos Islands and Haiti (d; two-tailed Wilcoxon signed-rank test, w = 97, P = 0.003, Hedge’s g = 0.60, n = 14). The data in c represent a second conditioning experiment conducted with the same turtles used in b and thus indicate that turtles can learn magnetic fields that exist at multiple locations. Remaining conventions are as in Fig. 1. Extended Data Fig. 2 shows the same data plotted on a linear scale. The maps were created using Natural Earth (https://www.naturalearthdata.com; credit Tom Patterson and Nathaniel Vaughn Kelso). Source data
Results of four additional map assay experiments, in which turtles discriminated between a magnetic field in which they were fed and a magnetic field in which they were not a–d, Turtles differentiated between magnetic fields that exist near: Delaware, USA, and Cuba (a; two-tailed Wilcoxon signed-rank test, w = 108, P = 0.04, Hedge’s g = 0.50, n = 16); Maine and Florida, USA (b; two-tailed Wilcoxon signed-rank test, w = 121, P = 0.004, Hedge’s g = 0.63, n = 16); Newfoundland, Canada and Virginia, USA (c; two-tailed Wilcoxon signed-rank test, w = 115, P = 0.01, Hedge’s g = 0.60, n = 16); and the Turks and Caicos Islands and Haiti (d; two-tailed Wilcoxon signed-rank test, w = 97, P = 0.003, Hedge’s g = 0.60, n = 14). The data in c represent a second conditioning experiment conducted with the same turtles used in b and thus indicate that turtles can learn magnetic fields that exist at multiple locations. Remaining conventions are as in Fig. 1. Extended Data Fig. 2 shows the same data plotted on a linear scale. The maps were created using Natural Earth (https://www.naturalearthdata.com; credit Tom Patterson and Nathaniel Vaughn Kelso). Source data
… 
Data from all map assay experiments analysed cumulatively a, Turtles learned to discriminate between a magnetic field in which they received food and one in which they did not (two-tailed Wilcoxon signed-rank test, w = 2,676, P = 1.6 × 10⁻⁸, Hedge’s g = 0.50, n = 78). Each dot represents an individual response. Remaining conventions are as in Fig. 1. Extended Data Fig. 3 shows the same data plotted on a linear scale. b, Percentage change in turtle dancing responses in the rewarded field relative to the unrewarded field for all conditioned turtles. For each turtle, percentage change was defined as: Rewardedfieldturtledancing−unrewardedfieldturtledancingunrewardedfieldturtledancing×100\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\frac{{\rm{R}}{\rm{e}}{\rm{w}}{\rm{a}}{\rm{r}}{\rm{d}}{\rm{e}}{\rm{d}}\,{\rm{f}}{\rm{i}}{\rm{e}}{\rm{l}}{\rm{d}}\,{\rm{t}}{\rm{u}}{\rm{r}}{\rm{t}}{\rm{l}}{\rm{e}}\,{\rm{d}}{\rm{a}}{\rm{n}}{\rm{c}}{\rm{i}}{\rm{n}}{\rm{g}}-{\rm{u}}{\rm{n}}{\rm{r}}{\rm{e}}{\rm{w}}{\rm{a}}{\rm{r}}{\rm{d}}{\rm{e}}{\rm{d}}\,{\rm{f}}{\rm{i}}{\rm{e}}{\rm{l}}{\rm{d}}\,{\rm{t}}{\rm{u}}{\rm{r}}{\rm{t}}{\rm{l}}{\rm{e}}\,{\rm{d}}{\rm{a}}{\rm{n}}{\rm{c}}{\rm{i}}{\rm{n}}{\rm{g}}}{{\rm{u}}{\rm{n}}{\rm{r}}{\rm{e}}{\rm{w}}{\rm{a}}{\rm{r}}{\rm{d}}{\rm{e}}{\rm{d}}\,{\rm{f}}{\rm{i}}{\rm{e}}{\rm{l}}{\rm{d}}\,{\rm{t}}{\rm{u}}{\rm{r}}{\rm{t}}{\rm{l}}{\rm{e}}\,{\rm{d}}{\rm{a}}{\rm{n}}{\rm{c}}{\rm{i}}{\rm{n}}{\rm{g}}}\times 100$$\end{document}. The red dashed line indicates a 0% change in turtle dancing behaviour relative to the unrewarded field. The dots represent the percentage change in turtle dancing for individual turtles. The percentage change in turtle dancing behaviour was significantly greater than 0 (one-tailed Wilcoxon signed-rank test, w = 2,833, P = 6.2 × 10⁻¹¹, Hedge’s g = 0.55, n = 78). Source data
Data from all map assay experiments analysed cumulatively a, Turtles learned to discriminate between a magnetic field in which they received food and one in which they did not (two-tailed Wilcoxon signed-rank test, w = 2,676, P = 1.6 × 10⁻⁸, Hedge’s g = 0.50, n = 78). Each dot represents an individual response. Remaining conventions are as in Fig. 1. Extended Data Fig. 3 shows the same data plotted on a linear scale. b, Percentage change in turtle dancing responses in the rewarded field relative to the unrewarded field for all conditioned turtles. For each turtle, percentage change was defined as: Rewardedfieldturtledancing−unrewardedfieldturtledancingunrewardedfieldturtledancing×100\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\frac{{\rm{R}}{\rm{e}}{\rm{w}}{\rm{a}}{\rm{r}}{\rm{d}}{\rm{e}}{\rm{d}}\,{\rm{f}}{\rm{i}}{\rm{e}}{\rm{l}}{\rm{d}}\,{\rm{t}}{\rm{u}}{\rm{r}}{\rm{t}}{\rm{l}}{\rm{e}}\,{\rm{d}}{\rm{a}}{\rm{n}}{\rm{c}}{\rm{i}}{\rm{n}}{\rm{g}}-{\rm{u}}{\rm{n}}{\rm{r}}{\rm{e}}{\rm{w}}{\rm{a}}{\rm{r}}{\rm{d}}{\rm{e}}{\rm{d}}\,{\rm{f}}{\rm{i}}{\rm{e}}{\rm{l}}{\rm{d}}\,{\rm{t}}{\rm{u}}{\rm{r}}{\rm{t}}{\rm{l}}{\rm{e}}\,{\rm{d}}{\rm{a}}{\rm{n}}{\rm{c}}{\rm{i}}{\rm{n}}{\rm{g}}}{{\rm{u}}{\rm{n}}{\rm{r}}{\rm{e}}{\rm{w}}{\rm{a}}{\rm{r}}{\rm{d}}{\rm{e}}{\rm{d}}\,{\rm{f}}{\rm{i}}{\rm{e}}{\rm{l}}{\rm{d}}\,{\rm{t}}{\rm{u}}{\rm{r}}{\rm{t}}{\rm{l}}{\rm{e}}\,{\rm{d}}{\rm{a}}{\rm{n}}{\rm{c}}{\rm{i}}{\rm{n}}{\rm{g}}}\times 100$$\end{document}. The red dashed line indicates a 0% change in turtle dancing behaviour relative to the unrewarded field. The dots represent the percentage change in turtle dancing for individual turtles. The percentage change in turtle dancing behaviour was significantly greater than 0 (one-tailed Wilcoxon signed-rank test, w = 2,833, P = 6.2 × 10⁻¹¹, Hedge’s g = 0.55, n = 78). Source data
… 
Mismatched field experiments a, Experimental design. Turtles conditioned to discriminate between magnetic fields near Maine and Florida (see Fig. 2b) were exposed to three magnetic fields: the rewarded field, the unrewarded field and one of two mismatched fields, consisting either of rewarded inclination and unrewarded intensity or unrewarded inclination and rewarded intensity. The map was created using Natural Earth (https://www.naturalearthdata.com; credit Tom Patterson and Nathaniel Vaughn Kelso). b, Amount of time spent turtle dancing. The field treatment was a significant predictor of time spent turtle dancing (see Extended Data Table 1; analysis of variance, F(2,30) = 5.9, P = 0.007). Benjamini–Hochberg pairwise comparisons indicated that turtles danced significantly longer in their rewarded field than in the unrewarded field (P = 0.01, Hedge’s g = 0.97) or to the mismatched fields (P = 0.01, Hedge’s g = 0.67); responses to the mismatched fields and the unrewarded field did not differ (P = 0.9, Hedge’s g = 0.032). Conventions are as in Fig. 3. c, Percentage change in turtle dancing behaviour relative to the unrewarded field. The red dashed line indicates a 0% change. One-tailed Wilcoxon signed-rank tests indicate that the percentage change significantly exceeded 0 for the rewarded field (w = 133, ***P = 0.00008, Hedge’s g = 0.88, n = 16), but not for either of the mismatched fields (w = 17, P = 0.58, Hedge’s g = 0.18, n = 8 for the unrewarded inclination and rewarded intensity field; w = 26, P = 0.16, Hedge’s g = 0.42, n = 8 for the rewarded inclination and unrewarded intensity field). Responses to the rewarded field were not equivalent to the responses to either of the mismatched fields (unrewarded inclination and rewarded intensity: Wilcoxon two one-sided tests (TOST), w = 50, P = 0.20); rewarded inclination and unrewarded intensity field: Wilcoxon TOST, w = 44, P = 0.12). The black dots represent individual responses. The boxes span the first to third quartile, the centre line represents the median, and the whiskers represent the 5th and 95th percentiles. NS, not significant. Source data
Mismatched field experiments a, Experimental design. Turtles conditioned to discriminate between magnetic fields near Maine and Florida (see Fig. 2b) were exposed to three magnetic fields: the rewarded field, the unrewarded field and one of two mismatched fields, consisting either of rewarded inclination and unrewarded intensity or unrewarded inclination and rewarded intensity. The map was created using Natural Earth (https://www.naturalearthdata.com; credit Tom Patterson and Nathaniel Vaughn Kelso). b, Amount of time spent turtle dancing. The field treatment was a significant predictor of time spent turtle dancing (see Extended Data Table 1; analysis of variance, F(2,30) = 5.9, P = 0.007). Benjamini–Hochberg pairwise comparisons indicated that turtles danced significantly longer in their rewarded field than in the unrewarded field (P = 0.01, Hedge’s g = 0.97) or to the mismatched fields (P = 0.01, Hedge’s g = 0.67); responses to the mismatched fields and the unrewarded field did not differ (P = 0.9, Hedge’s g = 0.032). Conventions are as in Fig. 3. c, Percentage change in turtle dancing behaviour relative to the unrewarded field. The red dashed line indicates a 0% change. One-tailed Wilcoxon signed-rank tests indicate that the percentage change significantly exceeded 0 for the rewarded field (w = 133, ***P = 0.00008, Hedge’s g = 0.88, n = 16), but not for either of the mismatched fields (w = 17, P = 0.58, Hedge’s g = 0.18, n = 8 for the unrewarded inclination and rewarded intensity field; w = 26, P = 0.16, Hedge’s g = 0.42, n = 8 for the rewarded inclination and unrewarded intensity field). Responses to the rewarded field were not equivalent to the responses to either of the mismatched fields (unrewarded inclination and rewarded intensity: Wilcoxon two one-sided tests (TOST), w = 50, P = 0.20); rewarded inclination and unrewarded intensity field: Wilcoxon TOST, w = 44, P = 0.12). The black dots represent individual responses. The boxes span the first to third quartile, the centre line represents the median, and the whiskers represent the 5th and 95th percentiles. NS, not significant. Source data
… 
Results of experiments with oscillating magnetic fields in the radiofrequency range (radiofrequency field experiments) a, Results of the map assay. Responses to the initial behavioural tests showed that turtles successfully learned to discriminate between magnetic fields that exist near Maine (the rewarded field) and near Florida (the unrewarded field); these data (grey bars) are reproduced from Fig. 2b as a convenient reference. In the radiofrequency field experiments, responses to the rewarded field did not differ regardless of whether radiofrequency (RF) was absent (blue bar) or present (red bar; two-tailed Wilcoxon signed-rank test, w = 65, P = 0.9, Hedge’s g = 0.076, n = 16). Each dot represents results from a single individual. Conventions are as in Fig. 3. b, Results from the compass and map assay. Turtles exposed to a magnetic field that exists near the Cape Verde Islands swam approximately westwards and were significantly oriented (Rayleigh test, r = 0.53, P = 0.0004, mean angle = 293.2° (95% CI = 269.5–324.5°), n = 26, left circular plot). Turtles exposed to the same Cape Verde field but with radiofrequency present had orientation statistically indistinguishable from random (Rayleigh test, r = 0.19, P = 0.42, mean angle = 47.9°, n = 24, right circular plot). The two distributions were significantly different (Watson test, U² = 0.35, P < 0.01). The dots represent the swimming directions of individual turtles; in the left circular diagram, the black arrow represents the mean swimming direction of the entire group, and the dashed lines represent 95% confidence intervals. Data are plotted relative to magnetic north. In a,b, blue indicates treatments without radiofrequency fields, and red corresponds to treatments with radiofrequency fields. Source data
Results of experiments with oscillating magnetic fields in the radiofrequency range (radiofrequency field experiments) a, Results of the map assay. Responses to the initial behavioural tests showed that turtles successfully learned to discriminate between magnetic fields that exist near Maine (the rewarded field) and near Florida (the unrewarded field); these data (grey bars) are reproduced from Fig. 2b as a convenient reference. In the radiofrequency field experiments, responses to the rewarded field did not differ regardless of whether radiofrequency (RF) was absent (blue bar) or present (red bar; two-tailed Wilcoxon signed-rank test, w = 65, P = 0.9, Hedge’s g = 0.076, n = 16). Each dot represents results from a single individual. Conventions are as in Fig. 3. b, Results from the compass and map assay. Turtles exposed to a magnetic field that exists near the Cape Verde Islands swam approximately westwards and were significantly oriented (Rayleigh test, r = 0.53, P = 0.0004, mean angle = 293.2° (95% CI = 269.5–324.5°), n = 26, left circular plot). Turtles exposed to the same Cape Verde field but with radiofrequency present had orientation statistically indistinguishable from random (Rayleigh test, r = 0.19, P = 0.42, mean angle = 47.9°, n = 24, right circular plot). The two distributions were significantly different (Watson test, U² = 0.35, P < 0.01). The dots represent the swimming directions of individual turtles; in the left circular diagram, the black arrow represents the mean swimming direction of the entire group, and the dashed lines represent 95% confidence intervals. Data are plotted relative to magnetic north. In a,b, blue indicates treatments without radiofrequency fields, and red corresponds to treatments with radiofrequency fields. Source data
… 
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Nature | Vol 638 | 27 February 2025 | 1015
Article
Learned magnetic map cues and two
mechanisms of magnetoreception in turtles
Kayla M. Goforth1,3 ✉, Catherine M. F. Lohmann1, Andrew Gavin2, Reyco Henning2,
Andrew Harvey1, Tara L. Hinton1, Dana S. Lim1 & Kenneth J. Lohmann1
Growing evidence indicates that migratory animals exploit the magnetic eld of the
Earth for navigation, both as a compass to determine direction and as a map to
determine geographical position1. It has long been proposed that, to navigate using a
magnetic map, animals must learn the magnetic coordinates of the destination2,3, yet
the pivotal hypothesis that animals can learn magnetic signatures of geographical
areas has, to our knowledge, yet to be tested. Here we report that an iconic navigating
species, the loggerhead turtle (Caretta caretta), can learn such information. When
fed repeatedly in magnetic elds replicating those that exist in particular oceanic
locations, juvenile turtles learned to distinguish magnetic elds in which they
encountered food from magnetic elds that exist elsewhere, an ability that might
underlie foraging site delity. Conditioned responses in this new magnetic map assay
were unaected by radiofrequency oscillating magnetic elds, a treatment expected
to disrupt radical-pair-based chemical magnetoreception4–6, suggesting that the
magnetic map sense of the turtle does not rely on this mechanism. By contrast,
orientation behaviour that required use of the magnetic compass was disrupted by
radiofrequency oscillating magnetic elds. The ndings provide evidence that two
dierent mechanisms of magnetoreception underlie the magnetic map and magnetic
compass in sea turtles.
Diverse animals migrate immense distances between specific areas used
in foraging, reproduction and seasonal sheltering
7–9
. How long-distance
migrant animals navigate to specific locations has remained enigmatic,
but the ability to exploit the magnetic field of the Earth as a source of
both directional information (that is, for a magnetic compass sense)
and positional information (that is, for a magnetic map sense) is an
important element in the navigational repertoire of many species
1,8,10
.
Magnetically sensitive animals can derive compass information
either from the direction (polarity) of field lines or from the relation-
ship between the tilt of magnetic field lines and gravity
10
. Magnetic map
information can be derived from several geomagnetic parameters that
vary predictably across the globe, including the intensity, or strength, of
the field and the inclination angle (the angle formed between magnetic
field lines and the surface of the Earth)1. The particular magnetic field
parameters that exist at a location, which are sometimes collectively
referred to as the ‘magnetic signature’ or ‘magnetic coordinates’ of a
site, can potentially provide an animal with a way to recognize a place
and return to it11–13.
Navigating to a known destination with a magnetic map presumably
requires an animal to learn and remember the magnetic signature of the
goal
2,3,12,13
. Nevertheless, despite strong evidence that sea turtles and
other animals possess magnetic maps
1
, an ability to learn the magnetic
signature of a location has yet to be demonstrated. Here we describe a
new behavioural assay in an iconic navigating species, the loggerhead
turtle (C. caretta), that relies on the ability of turtles to detect magnetic
map information. Our work provides direct evidence that an animal can
learn and remember the natural magnetic signature of a geographical
area. This ability may enable turtles and other animals to learn the
locations of ecologically important destinations and return to them
after long migrations.
A noteworthy feature of this new magnetic map assay is that turtles
respond to learned magnetic signatures without using the magnetic
compass; thus, the new assay effectively decouples the magnetic map
and compass senses. We used this decoupling to explore two major
questions of magnetic navigation research: first, how sea turtles
and other animals sense the magnetic field of the Earth, and second,
whether the same biophysical mechanism underlies the magnetic map
and compass. Using the magnetic map assay in combination with a sec-
ond, established assay that requires the magnetic compass, we report
strong evidence that two different mechanisms of magnetoreception
exist in sea turtles.
Learning magnetic signatures (map assay)
Sea turtles are renowned for their long-distance migrations and extraor-
dinary navigational abilities. At the beginning of their lives, logger
-
head turtles respond to magnetic signatures along their transoceanic
migratory route by swimming in directions that help them to remain
within favourable ocean currents and advance along the migratory
pathway14,15. Following this initial migration, turtles take up residence
https://doi.org/10.1038/s41586-024-08554-y
Received: 30 November 2023
Accepted: 19 December 2024
Published online: 12 February 2025
Check for updates
1Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA. 2Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
3Present address: Department of Biology, Texas A&M University, College Station, TX, USA. ✉e-mail: kmgoforth@tamu.edu
Content courtesy of Springer Nature, terms of use apply. Rights reserved
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  • Jun 2022
  • MAR BIOL
To understand the demographic responses of green turtles to seagrass decline, we examined a data set from study of a mixed-stock foraging aggregation of immature green turtles, Chelonia mydas, collected in Bermuda (32o18’N, − 64o46’W) over five decades. Average turtle size (SCLmin) and mass declined by 22.3% and 58.2%, respectively. Aggregation size structure shifted to smaller sizes and now consists of more small turtles and fewer large turtles. Density (turtles ha⁻¹) increased significantly but biomass (kg ha⁻¹) remained unchanged and low compared to C. mydas biomass observed elsewhere. Green turtles exhibited reduced site fidelity during two portions of the study period, suggesting increased foraging effort. Reduction in turtle body condition index and seagrass coverage occurred from offshore to inshore. Changes in aggregation composition and behavior were consistent with expectations given a documented decline in seagrass availability, combined with increased output from source rookeries. Apparent response to resource decline is traced back to 1976, well before seagrass loss was first documented. Green turtles and their primary food source (Thalassia testudinum) are at the northern limit of their range in Bermuda, where seagrasses would be expected to have a reduced tolerance for natural grazing pressure and increased susceptibility to synergistic stressors, especially temperature, bioturbation and phosphorus limitation. Our results suggest that synergistic stressors, and not green turtles alone, have produced the observed reduction in seagrasses on the Bermuda Platform. Given that seagrass declines have been reported worldwide, our findings may suggest how green turtles will respond elsewhere.
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Searching for unity in diversity of animal magnetoreception: From biology to quantum mechanics and back
Article
Full-text available
  • Mar 2022
How animals sense the geomagnetic field remains a mystery today. A remarkable diversity has been revealed in animal magnetoreception and several sophisticated models have been put forward in the past few decades, but none have been commonly accepted yet. Cryptochrome (Cry) has been proposed in both the radical pair model and the MagR/Cry-based biocompass model. How exactly it participates in magnetic sensing is an ongoing discussion. Here we wish to suggest an intermolecular electron transport (ET) pathway conserved in evolution in MagR/Cry complex, in which electron travels stepwise along a flavin-tryptophan chain as described in the classic radical pair model, and further extends to iron sulfur clusters in MagR via a series of stepping-stone amino acids as an ET bridge. The hypothesis we presented here may provide a solution to unite different models, and a feasible explanation for the intrinsic magnetic features of MagR, as well as a mechanism for signaling in animal magnetoreception, which are of considerable interest in both biology and physics.
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Environmental sources of radio frequency noise: potential impacts on magnetoreception
Article
Full-text available
  • Jan 2022
  • J COMP PHYSIOL A
Radio frequency electromagnetic noise (RF) of anthropogenic origin has been shown to disrupt magnetic orientation behavior in some animals. Two sources of natural RF might also have the potential to disturb magnetic orientation behavior under some conditions: solar RF and atmospheric RF. In this review, we outline the frequency ranges and electric/magnetic field magnitudes of RF that have been shown to disturb magnetoreceptive behavior in laboratory studies and compare these to the ranges of solar and atmospheric RF. Frequencies shown to be disruptive in laboratory studies range from 0.1 to 10 MHz, with magnetic magnitudes as low as 1 nT reported to have effects. Based on these values, it appears unlikely that solar RF alone routinely disrupts magnetic orientation. In contrast, atmospheric RF does sometimes exceed the levels known to disrupt magnetic orientation in laboratory studies. We provide a reference for when and where atmospheric RF can be expected to reach these levels, as well as a guide for quantifying RF measurements.
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Magnetic maps in animal navigation
Article
Full-text available
  • Jan 2022
  • J COMP PHYSIOL A
In addition to providing animals with a source of directional or ‘compass’ information, Earth’s magnetic field also provides a potential source of positional or ‘map’ information that animals might exploit to assess location. In less than a generation, the idea that animals use Earth’s magnetic field as a kind of map has gone from a contentious hypothesis to a well-established tenet of animal navigation. Diverse animals ranging from lobsters to birds are now known to use magnetic positional information for a variety of purposes, including staying on track along migratory pathways, adjusting food intake at appropriate points in a migration, remaining within a suitable oceanic region, and navigating toward specific goals. Recent findings also indicate that sea turtles, salmon, and at least some birds imprint on the magnetic field of their natal area when young and use this information to facilitate return as adults, a process that may underlie long-distance natal homing (a.k.a. natal philopatry) in many species. Despite recent progress, much remains to be learned about the organization of magnetic maps, how they develop, and how animals use them in navigation.
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Exploring Equivalence Testing with the Updated TOSTER R Package
Preprint
  • Nov 2022
Equivalence testing is arguably under utilized by experimental researchers. Due to limited software support for such analyses, and little education on the topic in graduate programs, the utilization of equivalence testings still appares to be low. One option for equivalence testing is the use of two one-sided tests (TOST). The TOSTER R package and jamovi module, originally developed by Daniel Lakens in 2017, was created to make TOST more accessible to the average researcher. In the past two years, I have made significant changes to the TOSTER package in order to increase its accessibility and provide more robust analysis options for researchers. In this paper, I will detail the changes to the package and highlight new analysis options that will make TOST easier for the average quantitative researcher.
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Cryptochrome-dependent magnetoreception in heteropteran insect continues even after 24 hours in darkness
Article
  • Sep 2021
  • J EXP BIOL
Sensitivity to magnetic fields is dependent on the intensity and color of light in several animal species. The of light-dependent magnetoreception working model points to Cryptochrome (Cry) as a protein able to cooperate with its cofactor flavin, which possibly becomes a magnetically susceptible pair upon excitation by light. What type of Cry is involved as well as what pair of magnetosensitive radicals are responsible is still elusive. Therefore, we developed a conditioning assay for the firebug (the firebug) Pyrrhocoris apterus, an insect species that possesses only the mammalian Cryptochrome (Cry II). Here, using the engineered Cry II null mutant, we show that: i) vertebrate-like Cry II is an essential component of the magnetoreception response, and ii) magnetic conditioning continues even after 25 hours in darkness. The light-dependent and dark-persisting magnetoreception based on Cry II may inspire new perspectives in magnetoreception and Cryptochrome research.
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