Magnetoreception in Rhodnius prolixus: Magnetic properties and behavioral experiments
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1
Universidad de los Andes, Biological Sciences Department, Colombia
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2
Universidad de los Andes, Physics Department, Colombia
Magnetoreception is a sensory system with a wide phylogenetic distribution present in bacteria, vertebrates and invertebrates. These organisms use this sensory mechanism for navigation and orientation. The three hypotheses of how organisms detect magnetic fields are: electromagnetic induction, radical pair mechanism and magnetite. The magnetite hypothesis predicts that crystals of magnetite associated to neurons will move when there is a change in the magnetic field, which leads to signal transduction. Rhodnius prolixus (vector of Chagas disease) is an insect with active dispersion from sylvatic populations. Understanding the mechanism of orientation in Rhodnius could help develop strategies of Chagas disease control.
In the present study magnetoreception by magnetite was tested in R. prolixus using behavioral and anatomical approaches. For the behavioral experiments adults of both sexes were tested individually during two and a half hours inside a closed petri dish divided in 4 quadrants. The number of body rotations and changes between quadrants were measured when a 1 mT artificial field was applied (using a Helmholtz coil) in a constant direction for 45 min and then rotated 180° every 5 min for 45 min. The same parameters were analyzed for 30 min once the field was turned off. A 30 min acclimation period was given and the field was turned on, turned off and rotated by an automation system. Insects were tested under dark conditions and recorded with a video camera under infrared light. In anatomical experiments, macerated bodies of R. prolixus and eight abdomens of Apis mellifera (as positive controls) were tested for magnetite using a VSM (vibrating sample magnetometer). Three different measurements were carried out for R. prolixus: i) complete body (N=4), ii) abdomen only (N=8), iii) head, thorax, and appendages (N=8).
The number of quadrant changes and body rotations of insects did not increase whether the artificial field was applied in a constant direction or rotated. A hysteresis curve was obtained for A. mellifera abdomens indicating the presence of ferromagnetic material in the tissue and the effectiveness of the VSM. When the whole body and separate parts of R. prolixus were tested a straight line with a negative slope was obtained in all cases, suggesting a diamagnetic behavior of the tissue and indicating no presence of magnetic material in the body.
Both approaches indicate that the magnetite model for magnetoreception is not present in R. prolixus. Nevertheless magnetoreception by radical pairs cannot be refuted. This is the first study to use a VSM magnetometer instead of a SQUID magnetometer for measurements in insect tissue. Although the SQUID methodology is more sensitive, some advantages make the VSM an interesting option for magnetoreception studies in animals: helium is not necessary, data processing is faster and it is more economic. The VSM is proposed as an alternative technique for detection of ferromagnetic material in insect tissue.
Acknowledgements
Financial support: Colciencias project 1204-459-21479 and Magnetism Laboratory Physics Department Universidad de los Andes.
Keywords:
Apis mellifera,
Magnetite,
Magnetoreception,
Rhodnius prolixus,
vibrating sample magnetometer
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for student poster award)
Topic:
Orientation and Navigation
Citation:
Giraldo
DA,
Hernández
CR and
Molina
JA
(2012). Magnetoreception in Rhodnius prolixus: Magnetic properties and behavioral experiments.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00435
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Received:
09 May 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Mr. Diego A Giraldo, Universidad de los Andes, Biological Sciences Department, Bogota, Colombia, da.giraldo263@uniandes.edu.co