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: 9.57). 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.
    Full-text · Article · Jan 2014 · Journal of Experimental Marine Biology and Ecology
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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). "

    Full-text · Dataset · Dec 2013
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    • "More controversial has been the question as to whether pigeons, and birds in general, use magnetic field intensity for position determination (“map”-step) during navigation, especially given that the discovery of an avian magnetoreceptor for a magnetic intensity seems as elusive as ever [3]. The likely existence of a magnetic map has been, however, demonstrated in the last decade in other animal groups with evidence for magnetic positioning-fixing having been accumulated for such a diverse array of species as lobsters [4], newts [5]–[6], marine turtles [7]–[8], and migratory birds [9]–[10]. "
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    ABSTRACT: It has long been thought that birds may use the Earth's magnetic field not only as a compass for direction finding, but that it could also provide spatial information for position determination analogous to a map during navigation. Since magnetic field intensity varies systematically with latitude and theoretically could also provide longitudinal information during position determination, birds using a magnetic map should be able to discriminate magnetic field intensity cues in the laboratory. Here we demonstrate a novel behavioural paradigm requiring homing pigeons to identify the direction of a magnetic field intensity gradient in a "virtual magnetic map" during a spatial conditioning task. Not only were the pigeons able to detect the direction of the intensity gradient, but they were even able to discriminate upward versus downward movement on the gradient by differentiating between increasing and decreasing intensity values. Furthermore, the pigeons typically spent more than half of the 15 second sampling period in front of the feeder associated with the rewarded gradient direction indicating that they required only several seconds to make the correct choice. Our results therefore demonstrate for the first time that pigeons not only can detect the presence and absence of magnetic anomalies, as previous studies had shown, but are even able to detect and respond to changes in magnetic field intensity alone, including the directionality of such changes, in the context of spatial orientation within an experimental arena. This opens up the possibility for systematic and detailed studies of how pigeons could use magnetic intensity cues during position determination as well as how intensity is perceived and where it is processed in the brain.
    Preview · Article · Sep 2013 · PLoS ONE
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