Analysis Of Magnetic Elements In Otoliths Of The Macula Lagena In Homing Pigeons With Inductively Coupled Plasma Mass Spectrometry

There are otolithic organs in the inner ear of vertebrates. During the evolution of vertebrates from fishes, to amphibians and reptiles, and then to birds and mammals, otolithic organs also evolve. Mammals have two otolithic organs, the utricle and the saccule. The macula lagena is another otolithic organ in the inner ear of non-mammals, and the lagena of more advaced birds develops better than that of lower animals. The particular status of the lagena during evolution attracts many researchers. Especially, the role of the lagena in birds'nervous systemn is of much interest.The macula lagena in birds is located at the apical end of the cochlea and contains many tiny otoliths. The macula lagena is innervated and has neural projections to the brainstem, but its physiological function is still unclear. It remains disputable that birds can obtain geomagnetic information for homing because otoliths in the lagena are rich in elements Fe and Zn. One of the key steps to clarify whether homing pigeons depend on magnetic elements in lagenal otoliths for navigation is to accurately find out whether the lagenal otoliths contain higher content of magnetic elements than the saccular and utricular otoliths. In the present study, I analyzed the contents of ferromagnetic elemetns (Fe, Co, Ni) and other metal elements in lagenal otoliths of adult homing pigeons with inductively coupled plasma mass spectrometry (ICP-MS) of high sensitivity(all the contents were normalized to Ca), and compared with those in saccular and utricular otoliths.The present study found that the contents of ferromagnetic elements (Fe, Co, Ni) in lagenal otoliths of adult homing pigeons were less than 0.7% (normalized to Ca element) and were the same order in magnitude as those in saccular and utricular otoliths. The content of Fe in lagenal otoliths was not significantly different from that in utricular otoliths and was even slightly lower than that in saccular otoliths. The content of Co in lagenal otoliths was slightly lower than that in saccular otoliths and slightly higher than that in utricular otoliths. The content of Ni in lagenal otoliths was not significantly different from that in saccular otoliths and was slightly higher than that in utricular otoliths. The contents of other metal elements Na, Mg, K, Al, Mn and Pb in lagenal otoliths were not significantly different from those in utricular and saccular otoliths. The contents of metal elements Zn, Ba and Cu in lagenal otoliths were slightly lower than those in saccular otoliths.Therefore, the present study does not support the hypothesis that birds depend on high contents of Fe and Zn in lagenal otoliths for sensation of geomagnetic information. Similarities in morphology, element ingredient and element content between otoliths in the lagena and those in the utricule suggest that the two types of otolithic organs may play a similar role in sensing gravitational and acceleration signals.