The Newts' Sixth Sense A talk given by Stefan H. Reissmann, written in the year 2007 AD. ( Translation of a modified version of the German original . )

This essay is essentially the translated version of a talk in German. Therefore, the terms used in this translation may not in all cases be the ones most common or most appropriate.

Literature Sources Mainly : Fischer, J.H. & Freake, M.J. & Borland, S.C. & Phillips, J.B. (2001) : » Evidence for the use of magnetic map information by an amphibian«. Animal Behaviour 62 : 1-10. Phillips, John B. (1987) : » Laboratory studies of homing orientation in the Eastern Redspotted Newt Notophthalmus viridescens «. The Journal of Experimental Biology 131 : 215-229. Phillips, John B. & Borland, S. Chris (1994) : » Use of a specialized magnetoreception system for homing by the Eastern Red-spotted Newt Notophthalmus viridescens «. The Journal of Experimental Biology 188 : 275-291.

Stefan H Reissmann

The Newts' Sixth Sense

AD 2007-02-14

Additionally : Anonymus : » Eastern Newt «. Wikipedia – the free encyclopedia (en.wikipedia.org). Anonymus : » Grünlicher Wassermolch «. Wikipedia – die freie Enzyklopädie (de.wikipedia.org). Brassart, J. & Kirschvink, J.L. & Phillips, J.B. & Borland, S.C. (1999) : » Ferromagnetic material in the Eastern Red-spotted Newt Notophthalmus viridescens «. The Journal of Experimental Biology 202 : 3155-3160. Deutschlander, Mark E. & Phillips, John B. & Borland, S. Chris (1999) : » The case for light-dependent magnetic orientation in animals «. The Journal of Experimental Biology 202 : 891-908.

More Recent Reports (found after 2007 AD) : Diego-Rasilla : F.J. & Luengo : R.M. & Phillips : J.B. (2005) → » Magnetic compass mediates nocturnal homing by the alpine newt, Triturus alpestris «. @ Behav. Ecol. Sociobiol. 58 : 361-365. Phillips : J.B. & Borland : S.C. & Freake : M.J. & Brassart : J. & Kirschvink : J.L. (2002) → » ‘Fixed-axis’ magnetic orientation by an amphibian: non-shoreward-directed compass orientation, misdirected homing or positioning a magnetite-based map detector in a consistent alignment relative to the magnetic field? «. @ The Journal of Experimental Biology 205 : 3903-3914. Sharifi : M. + Akia : F. + Elahi : M. (2008) → » Orientation Capacity of the Yellow Spotted Newt Neurergus microspilotus (Caudata: Salamandridae) «. @ Russian Journal of Herpetology 00 : 14. Sinsch : Ulrich (2007) → » Magnetic compass mediates nocturnal homing by the alpine newt, Triturus alpestris «. @ Ethology, Ecology & Evolution 19 : 201-214.

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Stefan H Reissmann

The Newts' Sixth Sense

AD 2007-02-14

Contents 1. The life cycle of the North-American Eastern Newts 2. The problem of retrieving the birth water 3. The discovery of the magnetic sense of the Eastern Newts 4. Magnetic compass and magnetic-field map 5. The Eastern Newts can navigate ! 6. How do the magnetic senses of the newts function physiologically ? 7. How and why can they use them in their daily life ?

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Stefan H Reissmann

The Newts' Sixth Sense

AD 2007-02-14

Text This article deals with the Eastern Newt Notophthalmus viridescens, which occurs in the central, eastern and southeastern North America in four subspecies. In many parts of its range, it is the most abundant species of caudates. Like most amphibians of the temperate latitudes its life cycle comprises an aquatic larval stage as well as an amphibic (or semi-terrestrial) adult stage. Yet, this life cycle differs much from most others, for it includes also an intermediate purely terrestrial stage, where the appearance of the juvenile newts is very different from that of the adult newts. This stage takes a couple of years and is called the red-eft stage, for these terrestrial juvenile newts are coloured reddish, orange, while the corresponding ground colour of the adults is greenish. The whole life cycle runs roughly as follows : The development starts in the egg. When the larva hatches, it has external gills, through which it breathes, mainly, while it lives, grows, and develops for some months in its birth water (pool). Then it metamorphoses and leaves the water. The red-eft stage has begun. During it, which takes some years, it stays on land, on the ground of woods. Then, after two to eight years, the colour of its body changes and it returns into the water. There it now spends almost the whole year again. It may leave the water, though, for example, to escape high temperatures. Finally, after up to about 15 years, which it may live in the wild, it dies. Most, more than two thirds, of the eastern Newts return as adults to the pond, where they had spent the first months of their life. And most of the remaining 20% to 30% settle in stretches of water only up to a mile away. Yet: How do the newts find back to their home pond? This problem they share with many other amphibian, which often make every year considerable 4 / 6

Stefan H Reissmann

The Newts' Sixth Sense

AD 2007-02-14

wanderings to the birth-waters. For Eastern Newts spend their often quite long youth as efts entirely on land, in its course, they may get far away from the stretch of water where they had grown up as larva. Thus, it might not be a wonder, that their have evolved a very special, exceptional sense of direction, which apparently is also developed in at least some but not all other members of their family. This sense of direction was apparently first discovered among amphibians in this species at the University of Indiana. There, it was found, that Eastern Newts seem to have a magnetic sense which endows them with the ability to perceive certain properties of the magnetic field of the earth. Strictly speaking, they have at least two different magnetic senses, which perceive different properties of the geomagnetic field each. One sense seems to serve the recognition of the direction alias declination of the magnetic field, whereas the other one detects either the strength or the inclination, that is its vertical tilt or dip, or, perhaps, even both. Since all three of the attributes of the geomagnetic field mentioned vary in space, they spread out a coordinate system, in which a map-like representation of the earth surface may be drawn. And this the central nervous system of the Eastern Newts apparently does, for they seems capable of real navigation. This means, that they can find back to their home pond from any place which is within the borders of their mental map without knowing the way, that is, without being able to get their bearings from known landmarks or from a calculated estimation of the way back on the basis of a knowledge of length and course of the way there. In order to do this, they must, on one hand, be able to guess the relation of their current position relative to their home place, thus need a kind of mental map to know, in which direction they have to go. To master this task, they may use the perceived declination and inclination or intensity of the geomagnetic field for orientation. On the other hand, the newts 5 / 6

Stefan H Reissmann

The Newts' Sixth Sense

AD 2007-02-14

must be able to determine the direction of their walk, need therefore a kind of inner compass. [This statement probably holds true only under certain circumstances, namely, when the map alone does not allow a recognition and tracking of the respective current position during the walk, which would be the case, if the landscape on the map looks very homogeneous.] As such an inner compass, the newts apparently use a magnetic-compass sense, with which they perceive the direction of the geomagnetic field, its declination. Perhaps, the Eastern Newts own even two different magnetic-compass senses, which are used in different situations. One of the magnetic-compass senses seems to be connected with the optical system, since it yields wrong values when the newts are illuminated with longwave light only. The magnetic-field-intensity or -inclination sense is independent of the light. It may be based on magnetic particles in the body of the newts, whose presence there has been proven. How the both, or maybe even three magnetic senses function, is still completely unknown, though. Moreover, it is also still a mystery, how the newts may actually benefit from their magnetic sense in their natural environment, for the differences in the magnetic field to which they are exposed there are much, about a hundred times, smaller than those used in the experiment and are subject to (relatively large) temporal oscillations, making it doubtful, that they can be used as basis for a mental map.

Stefan H. Reißmann

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