4

Spin Control Related

to Chemical Compass

of Migratory Birds

4.1

Introduction ...................................................................................... 145

4.2

Historical Background Study of the Radical Pair

Mechanism Models .......................................................................... 146

Magnetic Field Efects on Chemical Reactions via Radical Pair

Recombination • Magnetic Field Efects on Biological Systems via

Radical Pair Recombination

Hideyuki Okano

4.3

Magnetic Sense via Radical Pair Mechanism............................... 155

4.4

Radical Pair-Based Magnetoreceptor and Cryptochrome..........161

Chemical Characteristics of Cryptochrome • Magnetic Sense and

Tsukasa Shigemitsu

Cryptochrome

4.5

Discussion and Conclusions ........................................................... 169

Shoogo Ueno

References...................................................................................................... 177

4.1 Introduction

For all living organisms, sensing stimuli from the external environment such as light, sound, tempera­

ture, pressure, and chemical substances and taking actions in response to stimuli are important to sur­

vive. Tese living organisms have developed highly sensitive and specifc sensors in order to adapt to

their own environment. In particular, it is known that many bacteria, plants, and animals can perceive

the geomagnetic feld (GMF), which is a weak magnetic feld of about 50 μT, by using a certain kind of

highly sensitive magnetic sensor in their own bodies.

It is currently widely accepted that birds possess at least two, maybe even three (Wu and Dickman,

2011, 2012; see for a review, Mouritsen and Hore, 2012), magnetosensory systems: (1) a visually based

magnetosensor assumingly based on radical pair forming molecules in the retina (Ritz et al., 2000;

Mouritsen et al., 2004, 2005; Heyers et al., 2007; Zapka, 2009), and (2) a magnetoreceptor innervated

by the ophthalmic branch of the trigeminal nerve (V1) assumingly magnetite iron oxide nanoparticles

based and located in the upper beak (Beason and Semm, 1987; Semm and Beason, 1990; Fleissner et al.,

2003, 2007; Mora et al., 2004; Falkenberg et al., 2010; Heyers et al., 2010).

In the case of the radical pair forming molecules in the retina, it is strongly suggested that a blue-

light photoreceptor protein, “cryptochrome (CRY),” may play a crucial role as one of the highly sensitive

magnetic sensors (Ritz et al., 2000, 2004, 2009; Mouritsen and Ritz, 2005; Mouritsen and Hore, 2012; Lau

et al., 2012; Wiltschko and Wiltschko, 2014, Bolte et al., 2016; Kerpal et al., 2019; Wiltschko et al., 2021).

Challenging research studies have been conducted especially on migratory birds which may have highly

sensitive magnetic sensors (Ritz et al., 2000, 2004, 2009; Mouritsen and Ritz, 2005; Mouritsen and Hore,

DOI: 10.1201/9781003181354-4

145