Experimental evidence for a magnetic sense in Neotropical migrating butterflies (Lepidoptera: Pieridae)
Section snippets
Experimental disruption of the magnetic sense
Information that arises from the geomagnetic field may be disrupted by application of a strong magnetic field. This technique has been used successfully with migrating passerine birds (Wiltschko et al. 1994) and monarch butterflies (Perez et al. 1999). We applied a strong magnetic field to experimental butterflies, whereas a control group was handled in the same manner but a strong magnetic field was not applied. We predicted that unmanipulated control butterflies would adopt the natural
Natural Flight Directions
We captured butterflies flying over the Panama Canal (Lake Gatún) between 0900 and 1200 hours for midday experiments and for experiments the following morning (refer to Srygley et al. 1996 for a map of the flyway and Oliveira et al. 1998 for the phenology of the Aphrissa migration). Data were collected during the migratory seasons of 2001, 2002 and 2003 (specifically 24 June–7 July 2001, 13 May–23 July 2002 and 21 May–6 June 2003). Prior to capture of each butterfly as it migrated naturally
Strong Magnet Experiments
When released, control butterflies were significantly oriented on an axis (68° and 248°; axial analysis, Rayleigh test: r = 0.36, N = 57, P < 0.01; Fig. 1a). Before capture, these same butterflies had a mean orientation of 215° (±9°, 95% confidence interval; Fig. 1b). The 95% confidence interval for the released control butterflies (±28°) overlapped with the 95% confidence interval of the mean orientation before capture, but their axial orientation upon release was obviously different from their
Discussion
We have presented experimental evidence for a magnetic sense in migratory A. statira butterflies. Orientations of butterflies experimentally exposed to a strong magnetic field were significantly more dispersed than those of control butterflies. Significant differences between experimental and control groups indicate behavioural sensitivity to magnetic perturbation, although additional factors pertain in the interpretation of the orientational distributions. In addition, butterflies released
Acknowledgments
This research was funded with a grant from the National Geographic Society Committee for Research and Exploration. In addition, R.B.S. was supported by a Senior Postdoctoral Fellowship from the Smithsonian Institution Office of Fellowships and Grants, Washington, DC and the Korean Science and Engineering Foundation supported preparation of the manuscript. E.G.O. was supported by a CNPq Postdoctoral Fellowship. We thank the National Geographic Society and the Smithsonian Tropical Research
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Cited by (0)
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R. Dudley is at the Department of Integrative Biology, University of California-Berkeley, Berkeley, CA 94720-3140, U.S.A.
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E. G. Oliveira is at the Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, 30161-970 Belo Horizonte, MG, Brazil.
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A. J. Riveros is now at the Center for Insect Science, Arizona Research Laboratories, University of Arizona, 611 Gould-Simpson Science Building, 1040 E. Fourth, Tucson, AZ 35721-0101, U.S.A.