Darci M. S. Esquivel

Magnetoreception in eusocial insects: an update

Behavioural experiments for magnetoreception in eusocial insects in the last decade are reviewed. Ants and bees use the geomagnetic field to orient and navigate in areas around their nests and along migratory paths. Bees show sensitivity to small changes in magnetic fields in conditioning experiments and when exiting the hive. For the first time, the magnetic properties of the nanoparticles found in eusocial insects, obtained by magnetic techniques and electron microscopy, are reviewed. Different magnetic oxide nanoparticles, ranging from superparamagnetic to multi-domain particles, were observed in all body parts, but greater relative concentrations in the abdomens and antennae of honeybees and ants have focused attention on these segments. Theoretical models for how these specific magnetosensory apparatuses function have been proposed. Neuron-rich ant antennae may be the most amenable to discovering a magnetosensor that will greatly assist research into higher order processing of magnetic information. The ferromagnetic hypothesis is believed to apply to eusocial insects, but interest in a light-sensitive mechanism is growing. The diversity of compass mechanisms in animals suggests that multiple compasses may function in insect orientation and navigation. The search for magnetic compasses will continue even after a magnetosensor is discovered in eusocial insects.

Simple homemade apparatus for harvesting uncultured magnetotactic microorganisms

Descrevemos um aparato simples para a captura de microrganismos magnetotacticos nao cultivados. Este aparato consiste em um recipiente de vidro com duas aberturas. Uma abertura maior na parte superior e usada para introduzir o sedimento e a agua. O sedimento e a agua sao previamente armazenados em um recipiente semitampado, previamente testado para a presenca de bacterias magnetotacticas. O aparato e exposto a um campo magnetico, devidamente alinhado, em uma bobina feita a mao e as bacterias sao removidas pela extremidade capilar da segunda abertura do recipiente. As bacterias coletadas podem entao ser usadas em estudos ultraestruturais usando a tecnica de imagem espectroscopica eletronica. Um grande numero de bacterias consistindo de cocos e bastonetes foi eficientemente coletado de diferentes ambientes. Este aparato e util para estudos microbiologicos sobre microrganismos magnetotacticos nao cultivaveis, especialmente em abordagens moleculares para investigacoes filogeneticas que fornecem informacoes sobre a diversidade natural de comunidades microbianas.

Electron paramagnetic resonance study of the migratory ant Pachycondyla marginata abdomens.

Electron paramagnetic resonance was used to investigate the magnetic material present in abdomens of Pachycondyla marginata ants. A g congruent with 4.3 resonance of high-spin ferric ions and a very narrow g congruent with 2 line are observed. Two principal resonance broad lines, one with g > 4.5 (LF) and the other in the region of g congruent with 2 (HF), were associated with the biomineralization process. The resonance field shift between these two lines, HF and LF, associated with magnetic nanoparticles indicates the presence of cluster structures containing on average three single units of magnetite-based nanoparticles. Analysis of the temperature dependence of the HF resonance linewidths supports the model picture of isolated magnetite nanostructures of approximately 13 nm in diameter with a magnetic energy of 544 K. These particles are shown to present a superparamagnetic behavior at room temperature. The use of these superparamagnetic particle properties for the magnetoreception process of the ants is suggested.

Antennae: the strongest magnetic part of the migratory ant.

Pachycondyla marginata (P.m.), a migratory and termitophageous ant, hunting only the termite species Neocapritermes opacus,migrates significantly oriented 13° with respect to the magnetic North-South axis. Results of hysteresis curves at room temperature of four Pachycondyla marginata heads, thorax, pairs of antennae and abdomens, oriented parallel to the magnetic field, indicate that the antennae give the strongest saturation magnetization, suggesting this sensory organ as being also a magnetic sensory organ. The total saturation magnetization in a whole P.m. is composed by 42±3%, 24±3%, 19±3% and 15±3% of antennae, head, thorax and abdomen contributions, respectively. The abdomen hysteresis curve presents a wasp-waisted loop with Hcr/Hc of 4.75, characteristic of mixed magnetic systems.

Seasonal patterns in the orientation system of the migratory ant Pachycondyla marginata

Abstract. Route directions of migrations by the neotropical termite-hunting ant Pachycondyla marginata at a forest reserve in Southeast Brazil were analysed by circular statistic. Colony movement patterns were compared between the rainy/hot and dry/cold seasons. Migrations during the dry/cold season are significantly oriented 13° with the magnetic North–South axis, while rainy/hot migrations do not exhibit a preferred direction. This result is discussed considering the hypothesis that P. marginata ants may use the geomagnetic field as an orientation cue for migrations in the dry/cold season. The presence of magnetic iron oxides in the head and abdomen of P. marginata is consistent with this suggestion.

Stingless Bee Antennae: A Magnetic Sensory Organ?

Magnetic material in the body parts of the stingless bee Schwarziana quadripunctata, heads, pairs of antennae, thorax and abdomens, were investigated by SQUID magnetometry and Ferromagnetic Resonance (FMR). The saturation, Js and remanent, Jr, magnetizations and coercive field Hc are determined from the hysteresis curves. From Hc and Jr/Js the magnetic particle sizes are estimated. The Js and the FMR spectral absorption areas yield 23±3%, 45±5%, 15±2% and 19±4% magnetic material contributions of head, pair of antennae, thorax and abdomen, respectively, similar to those observed in the migratory ant Pachycondyla marginata. This result is discussed in light of the hypothesis of antennae as a magnetosensor structure.

Magnetic properties of the microorganism Candidatus Magnetoglobus multicellularis

Magnetotactic microorganisms use the interaction of internal biomineralized nanoparticles with the geomagnetic field to orientate. The movement of the magnetotactic multicellular prokaryote Candidatus Magnetoglobus multicellularis under an applied magnetic field was observed. A method using digital image processing techniques was used to track the organism trajectory to simultaneously obtain its body radius, velocity, U-turn diameter, and the reorientation time. The magnetic moment was calculated using a self-consistent method. The distribution of magnetic moments and radii present two well-characterized peaks at (9 ± 2) × 10−15 and (20 ± 3) × 10−15 A m2 and (3.6 ± 0.1) and (4.3 ± 0.1) μm, respectively. For the first time, simultaneous determination of the distribution of the organism radii and magnetic moment was obtained from the U-turn method by a new digital imaging processing. The bimodal distributions support an organism reproduction process model based on electron microscopy observations. These results corroborate the prokaryote multicellular hypothesis for Candidatus M. multicellularis.

Do geomagnetic storms change the behaviour of the stingless bee guiruçu (Schwarziana quadripunctata)

Six behavioural experiments were carried out to investigate the magnetic field effects on the nest-exiting flight directions of the honeybee Schwarziana quadripunctata (Meliponini). No significant differences resulted during six experiment days under varying geomagnetic field and the applied static inhomogeneous field (about ten times the geomagnetic field) conditions. A surprising statistically significant response was obtained on a unique magnetic storm day. The magnetic nanoparticles in these bees, revealed by ferromagnetic resonance, could be involved in the observed effect of the geomagnetic storm.

A study of magnetic properties of magnetotactic bacteria.

The first direct measurements of magnetic properties of magnetotactic bacteria from natural samples are presented. Measurements were made at 4.2 K, using a Superconducting Quantum Interfering Device (SQUID) magnetometer. From the magnetization results an anisotropy is obtained that is typical of magnetized ferro- or ferri-magnetic materials. The average magnetic moment of the bacteria determined from the results is in good agreement with the estimated moment from electron microscopy.

Biomineralization of a New Material by a Magnetotactic Microorganism

Magnetotactic bacteria were first observed by R.Blakemore when studying water sediments collected in Woods Hole (Massachusetts, USA)1. After his experimental work it was found that magnetotaxis is an orientation mechanism common to a large population of microorganisms and magnetotactic cells orient in a magnetic field, showing that the cell possesses a permanent magnetic dipole. 2 This experimental evidence suggests that the magnetic detector of such organisms is composed of minerals with permanent magnetization. Electron transmission microscopy of magnetotactic cells shows the presence of electron-dense regions with dimensions ranging from 400 to 1.500nm and geometric shapes. Until now all magnetotactic bacteria analysed present small crystals of Fe3O4, sometimes in an ordered distribution in the interior of the cell. The identification of magnetite in the cell cytoplasm was first made using Mossbauer spectroscopy on samples of Aquaspirillum magnetotacticum but Fe3O4 was later found in several other species of magnetotactic bacteria. Electron microscopy studies show evidence that crystals of Fe3O4 are enveloped by a membrane forming the magnetosome, a specialized organelle common to all magnetotactic cells 3–7.