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1Lost? Ask a Turtle: Navigation and Migration in Loggerheads by Giovanni Casotti Department of Biology West Chester University, West Chester, PA
2Terminology Navigation Migration Homing Moving along a course Moving from one region to anotherHomingReturning back to a specific pointThree definitions that deal with moving from point A to B.
3Migration Reproductive success Sockeye salmon (lifecycle migration and homing)Why migrate?There are numerous reasons for the migratory pathways seen in animals. Some have to do with reproduction. For example, Sockeye salmon in Alaska. Juveniles hatch and emerge from specific streams of the lake and inhabit the lake for 1-3 years. They then move out to sea and feed for another for another 2-3 years. When they reach sexual maturity they then migrate back to the lakes that they hatched from and spawn before dying. How salmon are able to navigate in the open ocean is not known.Salmon are able to return back to their birth streams as adults using chemical cues to help locate their natal rivers once they have arrived in the general vicinity of the river mouth; such cues also help guide salmon up the correct branches of rivers as they migrate to their spawning grounds.
4Migration Reproductive success Loggerhead turtles Elephant seals Loggerheads that hatch off the eastern coast of the U.S. migrate in a north east direction towards Europe then south following the coastline of Africa before turning west north west back towards the United States. The journey takes about 20 years. They return to the same beach that they originally hatched from and laying their eggs before heading back out to sea.Northern elephant seals travel between colonies along the west coast of North America and foraging areas in the North Pacific. They return to their home colonies to reproduce and rear their young.
5Case Study Loggerhead turtles How do hatchlings navigate to the ocean? What dangers are faced by newly emerging turtles hatchlings?Once in the water, what mechanism do hatchling turtles use to make their way toward open ocean?Once off the coast, juveniles make their way to the North Atlantic Current (Gyre). Describe this pathway.Answer these 3 questions in the case study based on the material covered in lecture and your readings from the journal articles.
6Migration Food acquisition Humpback whales A second reason to migrate is to acquire food. Humpback whales have the longest migratory pathway of any animal. In the winter they migrate toward the icecaps in both the northern and southern hemisphere to feed on fish and plankton which are in large supply. In the spring and summer they migrate toward warmer water of the equator to breed and give birth to their young.The best place to breed is not always the best place to feed.
7Navigation Strategies Trail followingEmployed by invertebrates only (ants)PilotingUsing landmarks to navigate (pigeons)There are 5 strategies involved when navigating.Trail following is used by invertebrates such as ants that leave a pheromone for others to follow, thus olfaction is the sense used. In this strategy each ant mirrors the path of the ant before it. I am sure you have seen this type of behavior before.Piloting is the use of local landmarks to navigate. Used in short navigational routes such as by pigeons. Experiments with homing pigeons and fitting them with translucent contact lenses shows that the birds can find their way back home but they cannot pinpoint their particular lofts accurately. This tells us that pigeons use visual cues to navigate, similar to what we as humans do.
8Navigation Strategies Path integrationEmployed by invertebrates only (ants)Path Integration This is a mechanism used by invertebrates such as ants. The animal is able to integrate compass headings and distance together away from a source then decrease the distance back to the original source by integrating information from the two.Return journey
9Navigation Strategies Map and compass navigationUsed by long distance migrators (whales and turtles)In addition to providing a source of compass information, the Earth’s field also provides a potential source of positional or ‘map’ information. Several geomagnetic elements vary in a predictable way across the surface of the Earth and might, in principle, be used to assess geographic location. For example, at each location on the globe, the magnetic field lines intersect the Earth’s surface at a specific inclination angle. At the magnetic equator, the field lines are parallel to the Earth’s surface, but become progressively steeper as one moves toward the magnetic poles. Thus, inclination angle varies predictably with latitude, and an animal able to detect this field element may be able to determine whether it is north or south of a particular area. Similarly, the intensity of the total field, or the intensity of the horizontal and vertical field components, might also hypothetically be used in position finding.
10Terrestrial Animals Compass navigation Using Earth’s magnetic field Compass navigation is a mechanism of navigation proposed to be used by sea turtles. In this experiment a line was connected to a harness and each turtle was tethered to an electronic tracking system in the center of a circular pool of water. Turtles could therefore swim in any direction while the tracking system monitored the direction toward which the turtle swam. This information was relayed to a computer.The pool of water was surrounded by a large coil consisted of numerous strands of wire. When the coil system was turned on, it reversed the direction of the magnetic field around the turtles.Turtles exposed to a magnetic field equivalent to that existing 337 km north of the test site oriented themselves roughly southwards. By contrast, those exposed to a field matching that of an area 337 km south of the test site swam approximately northwards. The two distributions are significantly different indicating that turtles can distinguish between the magnetic fields that characterize different geographic locations within their usual environment.The results demonstrate that hatchling loggerhead and leatherback sea turtles have the ability to detect the Earth's magnetic field and use it as an orientation cue.Source: Lohmann, K. J. and Lohmann, C.E. (1994). Detection of magnetic inclination angle by sea turtles: A possible mechanism for determining latitude. J. Exp. Biol. 194:
11Watch the video on turtle navigation: Case StudyWatch the video on turtle navigation:As you go through the video carefully listen the description of the different types on navigation cues used by the turtles.
12Magnetite Receptors Located in beaks of birds The video talks about particles called magnetite located in the heads of the turtles. Many birds possess the same mechanism.Magnetoreceptors in the bill of a homing pigeon. (A) Pigeon head showing location of nerves in the upper beak thought to play a role in magnetoreception. (B) The upper beaked viewed from below showing the location (the six white spots) of iron oxide particles. (C) Diagram of the end of a neuron (dendrite) containing a non-magnetic vesicle, several clusters of magnetite crystals, and chains of iron-bearing platelets (From: Pósafi and Dunin-Borkowski 2009)Each dendrite senses only one direction of the magnetic field (Fleissner et al. 2007), but there are several dendrites with different alignments so birds can monitor different directions of the magnetic field.
13Magnetite Receptors 2 possible mechanisms of action Top, A chain of magnetite crystals is attached by protein strands to ion channels in a nerve cell membrane. Ion channels open, causing nervous impulses, and close in response to the magnetic field (indicated by the arrow). B). Bottom, Vesicles (black circles) filled with magnetite particles are attached to a membrane by protein strands and, in response to the external magnetic field (arrow, B) the vesicles move towards each other, deforming the membrane, opening the ion channels, and triggering a nervous impulse (From: Pósfai and Dunin-Borkowski 2009).Changes in the direction and strength of the magnetic field cause ion channels associated with the magnetoreceptors to open or close (Figure above), and the resulting nervous impulses provide birds with information about the magnetic field. Because of the differing alignments of the dendrites, these receptors appear to act as a three-axis magnetometer, allowing birds to sense both magnetic field duration and the strength or intensity of the magnetic field
14Case StudyQuestionHow do hatchling and adult turtles find their way along their migratory pathway? What methods did scientists use to identify the mechanism responsible for long distance navigation in sea turtles?Question #1. Their migratory pathway being the North Atlantic Gyre.
15Navigation Strategies Compass navigationUsing the sun (starlings)SunlightSome animals use the sun. Experiments with starlings show that these animals migrate along certain compass bearings depending on the location of the sun.Fig. A. Birds were placed in a circular cage with a window through which sunlight was shone. Birds fluttered to align themselves in the direction they would normally travel if they were free.Fig. B. The angle of the sun was deflected with a mirror. Birds maintained the same relative position as in Fig. A. These experiments demonstrate that the birds use the sun as a compass.Adapted from Fig , page 603 In: Hickman CP, Roberts, L.S. Keen, SL, Larson, A., I’Anson, H and Eisenhour, D.J. (2008). Integrated Principles of Zoology. 14th ed. McGraw-Hill, Boston. ISBN
16Navigation Strategies Compass navigationUsing the stars (Indigo buntings)Indigo buntings use the stars to navigate. In a planetarium experiment if the star position is reversed (numbers represent degree of orientation) buntings alter their position and attempt to migrate in the opposite direction.Modified from: Emlen, ST (1967). Migration orientation in the Indigo Bunting, Passerina cyanea: Part 1 Evidence for the use of celestial cues. The Auk, 84: (3)
17Navigation Strategies Olfactory cues: Detection of dimethyl sulphide (DMS)Over the seemingly featureless ocean environment sea birds such as petrels and albatrosses can detect local emissions of scents released by phytoplankton such as dimethyl sulphide.These are important because such features enable birds to detect shelf breaks and seamounts. These studies suggest an odor landscape that may provide birds with orientation cues.In the experimental results above (A) heart rate increased in birds exposed to DMS. In (B) birds were able to detect MDS presented to them in a maze as opposed to C control and NC, made no choice.
18Case StudyQuestionsBirds might use DMS to navigate. What produces DMS and what methods did researchers use to determine this? In what oceans has DMS been measured?What about seals? Why do the researchers think that seals use visual cues to navigate?Over the seemingly featureless ocean environment, local emissions of scents released by phytoplankton reflect bathymetric features such as shelf breaks and seamounts. These features suggest an odor landscape that may provide birds with orientation cues.One of the journal articles you are asked to read is on navigation in seals. These animals are also long transoceanic migrators. The researchers state that these animals rely heavily on visual cues in sight of landfall. Why do the researchers think that?
19Case StudyQuestionsWhy did the researchers discount the possibility of geomagnetic, celestial, acoustic and olfactory cues as navigational tools in seals?Migrating in the open ocean can be more challenging than a land migration. Describe these differences.Along those same lines the researchers discount other possibilities such as geomagnetic, celestial, acoustic and olfactory senses. Why did they discount these as possibilities?Finally, put together your knowledge of open ocean and land migration and describe differences between the two landscapes.
21Slide 8Created by author.Slide 9NASA,Slide 10Schematic of experimental setup and photo of turtle in harness provided by The Lohman Lab, Department of Biology, University of North Carolina, Chapel Hill, NC (http://www.unc.edu/depts/geomag/), used with permission.Slide 12Figure 7 in:Pósafi, M., and R. E. Dunin-Borkowski Magnetic nanocrystals in organisms. Elements 5: Used with the permission of the Mineralogical Society of America.Slide 13Panels B and C of Figure 4 in:Slide 15Adapted from Fig , page 603 In: Hickman CP, Roberts, L.S. Keen, SL, Larson, A., I’Anson, H and Eisenhour, D.J. (2008). Integrated Principles of Zoology. 14th ed. McGraw-Hill, Boston. ISBNSlide 16Modified from: Emlen, ST (1967). Migration orientation in the Indigo Bunting, Passerina cyanea: Part 1 Evidence for the use of celestial cues. The Auk, 84: (3) https://sora.unm.edu/sites/default/files/journals/auk/v084n03/p0309-p0342.pdfSlide 17Figure 1 in: Nevitt, G. A. and Bonadonna, F Sensitivity to dimethyl sulphide suggests a mechanism for olfactory navigation by seabirds. 1: Available online at Used with permission.