Article

Longitude Perception and Bicoordinate Magnetic Maps in Sea Turtles

Department of Biology, University of North Carolina, Chapel Hill, Chapel Hill, NC 27599, USA.
Current biology: CB (Impact Factor: 9.92). 02/2011; 21(6):463-6. DOI: 10.1016/j.cub.2011.01.057
Source: PubMed

ABSTRACT Long-distance animal migrants often navigate in ways that imply an awareness of both latitude and longitude. Although several species are known to use magnetic cues as a surrogate for latitude, it is not known how any animal perceives longitude. Magnetic parameters appear to be unpromising as longitudinal markers because they typically vary more in a north-south rather than an east-west direction. Here we report, however, that hatchling loggerhead sea turtles (Caretta caretta) from Florida, USA, when exposed to magnetic fields that exist at two locations with the same latitude but on opposite sides of the Atlantic Ocean, responded by swimming in different directions that would, in each case, help them advance along their circular migratory route. The results demonstrate for the first time that longitude can be encoded into the magnetic positioning system of a migratory animal. Because turtles also assess north-south position magnetically, the findings imply that loggerheads have a navigational system that exploits the Earth's magnetic field as a kind of bicoordinate magnetic map from which both longitudinal and latitudinal information can be extracted.

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Available from: Kenneth Lohmann, Dec 05, 2014
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    • "As with most populations of sea turtles, there is no information regarding oceanic navigation in hawksbill hatchlings and juveniles from Brazil. Numerous studies on loggerheads from the eastern coast of Florida, U.S.A. have shown that hatchlings inherit detailed orientation instructions with respect to spatial variation in the Earth's magnetic field (Fuxjager et al., 2011; Lohmann et al., 2001, 2012; Putman et al., 2011). Specifically, pairings of magnetic intensity and inclination angle that exist along the North Atlantic Gyre elicit directional swimming responses in newly hatched turtles under laboratory conditions (Lohmann et al., 2012). "
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    ABSTRACT: Long-distance dispersal and ontogenetic shifts in habitat use are characteristic of numerous marine species and have important ecological, evolutionary, and management implications. These processes, however, are often challenging to study due to the vast areas involved. We used genetic markers and simulations of physical transport within an ocean circulation model to gain understanding into the origin of juvenile hawksbill sea turtles (Eretmochelys imbricata) found at Ascension Island, a foraging ground that is thousands of kilometers from known nesting beaches. Regional origin of genetic markers suggests that turtles are from Western Atlantic (86%) and Eastern Atlantic (14%) rookeries. In contrast, numerical simulations of transport by ocean currents suggest that passive dispersal from the western sources would be negligible and instead would primarily be from the East, involving rookeries alongWestern Africa (i.e., Principe Island) and, potentially, from as far as the Indian Ocean (e.g.,Mayotte and the Seychelles). Given that genetic analysis identified the presence of a haplotype endemic to Brazilian hawksbill rookeries at Ascension, we examined the possible role of swimming behavior by juvenile hawksbills from NE Brazil on their current-borne transport to Ascension Island by performing numerical experiments in which swimming behavior was simulated for virtual particles (simulated turtles). We found that oriented swimming substantially influenced the distribution of particles, greatly altering the proportion of particles dispersing into the North Atlantic and South Atlantic. Assigning location-dependent orientation behavior to particles allowed them to reach Ascension Island, remain in favorable temperatures, encounter productive foraging areas, and return to the vicinity of their natal site. The age at first arrival to Ascension (4.5–5.5years) of these particles corresponded well to estimates of hawksbill age based on their size.Our findings suggest that ocean currents and swimming behavior play an important role in the oceanic ecology of sea turtles and other marine animals.
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    • "As with most populations of sea turtles, there is no information regarding oceanic navigation in hawksbill hatchlings and juveniles from Brazil. Numerous studies on loggerheads from the eastern coast of Florida, U.S.A. have shown that hatchlings inherit detailed orientation instructions with respect to spatial variation in the Earth's magnetic field (Fuxjager et al., 2011; Lohmann et al., 2001, 2012; Putman et al., 2011). Specifically, pairings of magnetic intensity and inclination angle that exist along the North Atlantic Gyre elicit directional swimming responses in newly hatched turtles under laboratory conditions (Lohmann et al., 2012). "
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    • "Whilst it is now well established that loggerhead turtle hatchlings can respond behaviourally to changes in magnetic inclination and intensity (Lohmann et al. 2001; Merrill and Salmon 2010; Putman et al. 2011), it remains equivocal whether such information could only be used proWtably by adult turtles when they are large and powerful swimmers able to swim strongly relative to currents (e.g. Luschi et al. 2007; Mencacci et al. 2010). "
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    ABSTRACT: Whilst a range of animals have been shown to respond behaviourally to components of the Earth’s magnetic field, evidence of the value of this sensory perception for small animals advected by strong flows (wind/ocean currents) is equivocal. We added geomagnetic directional swimming behaviour for North Atlantic loggerhead turtle hatchlings (Caretta caretta) into a high-resolution (1/4°) global general circulation ocean model to simulate 2,925-year-long hatchling trajectories comprising 355,875 locations. A little directional swimming (1–3 h per day) had a major impact on trajectories; simulated hatchlings travelled further south into warmer water. As a result, thermal elevation of hatchling metabolic rates was estimated to be between 63.3 and 114.5% after 220 days. We show that even small animals in strong flows can benefit from geomagnetic orientation and thus the potential implications of directional swimming for other taxa may be broad.
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