A geomagnetic declination compass for horizontal orientation in fruit flies

Abstract

The Earth's geomagnetic field (GMF) is known to act as a sensory cue for magnetoreceptive animals such as birds, sea turtles, and butterflies in long-distance migration, as well as in flies, cockroaches, and cattle in short-distance movement or body alignment. Despite a wealth of information, the way that GMF components are used and the functional modality of the magnetic sense are not clear. A GMF component, declination, has never been proven to be a sensory cue in a defined biological context. Here, we show that declination acts as a compass for horizontal food foraging in fruit flies. In an open-field test, adopting the food conditioning paradigm, food-trained flies significantly orientated toward the food direction under ambient GMF and under eastward-turned magnetic field in the absence of other sensory cues. Moreover, a declination change within the natural range, by alteration only of either the east-west or north-south component of the GMF, produced significant orientation of the trained flies, indicating that they can detect and use the difference in these horizontal GMF components. This study proves that declination difference can be used for horizontal foraging, and suggests that flies have been evolutionarily adapted to incorporate a declination compass into their multimodal sensorimotor system.

Blue light-dependent human magnetoreception in geomagnetic food orientation

“…In the testing room, the ambient GMF had a total intensity of 50 μT, inclination of 53°, and declination of −7° (Daegu city, Republic of Korea). To provide the subjects with different GMF-like magnetic fields, i.e., with the same total intensity and inclination, but different direction for magnetic north, a rectangular Helmholtz coil system used in our previous studies [10, 47] was double-wrapped and electrically-grounded with copper mesh shielding [48], and used to generate static magnetic fields as described [10, 47]. Briefly, the dimensions of the coils were 1,890 × 1,890 mm, 1,890 × 1,800 mm, and 1,980 × 1,980 mm, for the X, Y, and Z axes, respectively.…”

Behavioral evidence for geomagnetic imprinting and transgenerational inheritance in fruit flies

“…Fly Stock. Flies from the Canton-S strain were obtained from the Bloomington Drosophila Stock Center (Indiana University, Bloomington, IN) and reared on a standard cornmeal-yeast-agar diet, as described in previous studies (17,19,31). Briefly, rearing conditions were 25°C ± 0.5°C, 60 ± 2% relative humidity, and a 12 h/12 h light/dark cycle under a full-spectrum (350 to 800 nm) light-emitting diode light (∼500 l× = 3.03 × 10 14 photons/cm 2 /s), which was turned on and off at 0900 and 2100 (local time), respectively.…”

“…MF Modulation. A rectangular, double-wrapped (32) Helmholtz coil system modified from previous studies (17,19,31) and consisting of 3 pairs of parallel coils arranged orthogonally for the 3 axes was used to generate GMF-like MFs. Briefly, the coil for the X-axis (north-south) was aligned with true north so that the Y-coil (east-west axis) could be modulated for the Y component of the GMF.…”

“…The Drosophila fruit fly can orient magnetically and is a useful model system for studying magnetoreception (14)(15)(16)(17). Recent studies have reported that a static MF can disrupt innate negative geotactic behavior in flies (18), and an earth-strength MF was found to be a sensory cue for positive geotaxis of starved fruit flies in a food-conditioning assay, modulating vertical foodsearch movement (19).…”

Declination affects geomagnetic field‐modulated geotaxis in fruit flies

“…Moreover, variation in the degree of declination is substantially enhanced by local magnetic anomalies attributable to natural structures, such as mountains, rocks and volcanic deposits, as well as manmade structures (Finlay et al 2010; Thébault et al 2015; Honsho et al 2016). In contrast to the total intensity or inclination, the potential effect of declination on horizontal magnetic movement has been explored in a few species, including birds, cockroaches and flies (Bazalova et al 2016; Chernetsov et al 2017; Lee et al 2018). However, the potential effect of declination on vertical movement in magnetosensitive organisms has not been reported.…”