Spontaneous preferences for magnetic compass direction in the American red-spotted newt, Notophthalmus viridescens (Salamandridae, Urodela)

Abstract

In addition to other sensory modalities, migratory vertebrates are able to use the earths' magnetic field for orientation and navigation. The magnetic cue may also serve as a reference for other orientation mechanisms. In this study, significant evidence is shown that, even in darkness, newts (Notophthalmus viridescens, Salamandridae) spontaneously align according to the natural or to the deviated earth's magnetic field lines, thereby demonstrating a magnetic compass sensitivity. All newts preferred compass directions close to east or west or chose the E/W axially and hence sought to maintain a specific angle or axis relative to the magnetic field vector. Such an active alignment is considered an essential precondition for magnetic orientation. When the horizontal magnetic vector was experimentally compensated, animals became disoriented. We infer that the animals have either learned the preferred magnetic direction/axis individually or that these choices are innate and could even be seasonally different as in migrating birds. It is still an unanswered question as to how and where the physical and physiological mechanisms of magnetic transduction and reception take place. The visual system and other light-dependent (radical pairs) mechanisms alone are often claimed to be in function, but this must now be reconsidered given the results from animals when deprived of light. The results may therefore point to putative receptor mechanisms involving magnetite elements in specialized magneto-receptors.

Innate preference for magnetic compass direction in the Alpine newt, Triturus alpestris (Salamandridae, Urodela)?

“…obvious ''landmarks''). So far, we can only tentatively suggest this for N. viridescens, as we were not able to obtain offspring (Schlegel 2006), but, for T. alpestris, strong hints of innate and learned magnetic alignment will now be demonstrated by comparing the magnetic aligning of parents and the F 1 generation.…”

“…These were the same as described in Schlegel (2006), i.e. normal = natural local field, reversed (mN = S; horizontal vector angle deviated by 180°, vector strength as under natural conditions), and comp.…”

“…The performance of urodeles to align according to magnetic fields in the dark was studied by a classical method adapted from Wiltschko and Merkel (1966) Wiltschko (1968) and Wiltschko andWiltschko (1972, 1988); see Schlegel (2006).…”

“…Schlegel 2006) clearly demonstrated that all specimens tested (adults) of N. viridescens spontaneously and significantly preferred magnetic directions close to the E/W axis, regardless of holding conditions. The majority of adults tested in their very first sessions even preferred magnetic E to W (17:5, in their 22 first sessions ;Schlegel 2006). These animals had not been conditioned to particular (magnetic) directions in a known behavioural situation, as in shoreline orientation (Phillips 1986), but presumably followed their innate target direction.…”

Photoreceptor-based magnetoreception: optimal design of receptor molecules, cells, and neuronal processing

“…Behavioural studies have provided more information about the functional properties of magnetic compasses in a variety of animals (Rappl et al 2000;Wiltschko et al 2000aWiltschko et al ,b, 2001Wiltschko et al , 2002bWiltschko et al , 2003aWiltschko et al , 2004aWiltschko et al ,b, 2005Wiltschko et al , 2006Wiltschko et al , 2007aÅ kesson et al 2001;Phillips et al 2001Phillips et al , 2002Muheim et al 2002Muheim et al , 2006Irwin & Lohmann 2003;Mouritsen et al 2003Mouritsen et al , 2004aCochran et al 2004;Prior et al 2004;Vacha & Soukopova 2004;Freake & Phillips 2005;Gould 2005;Thalau et al 2006;Pazur et al 2007;Schlegel 2007;Voss et al 2007;Dommer et al 2008;Feenders et al 2008;Rogers et al 2008;Stapput et al 2008;Vacha et al 2008aVacha et al ,b, 2009Keary et al 2009;Zapka et al 2009;Hein et al 2010;Wilzeck et al 2010) and biophysical and physiological studies have provided more information about the cryptochrome suggestion (Giovani et al 2003;Möller et al 2004;Mouritsen et al 2004bAhmad et al 2007;...…”