Natural Experiments Indicate That Geomagnetic Variations Cause Spatial and Temporal Variations in Coconut Palm Asymmetry

Abstract

In plants with alternately arranged foliage, such as the coconut palm (Cocos nucifera), leaves are attached to the stem in either an ascending clockwise (left handed [L]) or counterclockwise (right handed [R]) spiral (Fig. 1). Foliar spiral direction (FSD) is not genetically determined in coconut palms: All crosses (R 3 R, R 3 L, L 3 R, L 3 L) yield R and L progeny in approximately equal numbers (Davis, 1962;Louis and Chidambaram, 1976;Toar et al., 1979). FSD is, thus, a classic case of morphological asymmetry in which dextral and sinistral forms are not inherited and are equally common within a species (Palmer, 2005). FSD would seem a simple stochastic process unworthy of further study if not for the observation by T.A. Davis, based on data collected from over 70,000 coconut palms in over 40 locations around the world, that the FSD of coconut palms varies with latitude: R trees predominate in the northern hemisphere and L trees predominate in the southern hemisphere (Davis and Davis, 1987). A reanalysis of Davis's data indicated that these hemispheric asymmetries in FSD are significantly better correlated with magnetic (dip) latitude than with geographic or geomagnetic (centered dipole) latitude, suggesting that latitudinal asymmetries in FSD might be associated with the temporally varying component of the Earth's magnetic field (Minorsky, 1998). Here, we report that asymmetries in FSD are also evident in populations of coconut palms on opposite sides of islands and that asymmetries between cohorts vary with an 11-year periodicity-two novel discoveries consistent with the hypothesis that geomagnetic variations underlie asymmetries in coconut palm FSD.Whereas the effects of the geomagnetic field on the orientation of magnetotactic bacteria and various animals, particularly insects and migratory birds, has been extensively studied, relatively little is known about the effects of geomagnetism on plants (Belyavskaya, 2004; Galland and Pazur, 2005). Important questions remain unanswered, such as whether or not plants perceive the geomagnetic field and, if they do, by what mechanisms and to what possible advantage, if any? At this early stage in our understanding of magnetoreception, several alternative mechanisms are being discussed by biophysicists concerning how cells might sense weak electromagnetic fields. Among the proposed modes of action are (1) torque on ferromagnetic particles; (2) modulation of biochemical reactions that involve spin-correlated radical pairs (radical-pair mechanism); (3) modulation of the transport rates and binding by ion-cyclotron resonance; and (4) quantum coherence mechanisms (for review, see Galland and Pazur, 2005). Regardless of the exact mechanisms involved in the physical reception of magnetic stimulation, considerable evidence suggests the involvement of biological membranes, in general (Balcavage et al.

Do geomagnetic variations affect plant function?

“…Based on these findings, Minorsky (1998) proposed that asymmetries in coconut palm FSD result from the Earth currents induced by variations in the vertical Z component of the geomagnetic field that cause a rotational bias in the axial migration of morphogens (e.g., auxin transporters) in coconut palm embryos. Minorsky and Bronstein (2006) presented two new lines of evidence that geomagnetic variations may underlie asymmetries in coconut palm FSD. First, they showed that asymmetries occur in the FSD of palm populations on opposite sides of islands, and second, that asymmetries in FSD vary with the sunspot cycle.…”

“…More recently, Minorsky and Bronstein (2006), studying coconut palms, have presented evidence that geomagnetic storms may affect another process in plants, namely the manner in which leaves are attached to the stem. In coconut palms, leaves are attached to the stem in either a left-handed (L) or right-handed (R) spiral.…”

“…Using data provided by Davis (1963), Minorsky and Bronstein (2006) also examined whether asymmetry in FSD varies with the solar cycle. Of the 384 trees in Davis's (1963) data set, 375 fell into one of nine cohorts of 22 trees or more.…”

“…The ''geomagnetic island effect'' is characterized by a complete reversal of the vertical Z component of short-period geomagnetic field anomalies at observation points on opposite sides of islands (Yamaguchi et al, 1992). To examine whether FSD varied around the circumferences of islands, Minorsky and Bronstein (2006) collected data on six islands (Puerto Rico, n ¼ 4850; Antigua, n ¼ 2038; Hawaii, n ¼ 3552; Maui, n ¼ 2175; Tahiti, n ¼ 1635; Moorea, n ¼ 2116).…”

“…In the last few years, there has been a reawakening of interest in the idea that plants may be sensitive to geomagnetic variations (Belyavskaya, 2004;Galland and Pazur, 2005;Minorsky and Bronstein, 2006). There are also numerous neglected reports in the botanical literature concerning unexplained periodic plant behaviors that exhibit frequencies similar to those of many well-known geophysical periodicities.…”