B41A-01
Sensory signals and neuronal groups involved in guiding the sea-ward motor behavior in turtle hatchlings of Chelonia agassizi
Turtle hatchlings orient display sea-ward oriented movements as soon as they emerge from the nest. Although most studies have emphasized the role of the visual information in this process, less attention has been paid to other sensory modalities. Here, we evaluated the nature of sensory cues used by turtle hatchlings of Chelonia agassizi to orient their movements towards the ocean. We recorded the time they took to crawl from the nest to the beach front (120m long) in control conditions and in visually, olfactory and magnetically deprived circumstances. Visually-deprived hatchlings displayed a high degree of disorientation. Olfactory deprivation and magnetic field distortion impaired, but not abolished, sea-ward oriented movements. With regard to the neuronal mapping experiments, visual deprivation reduced dramatically c-fos expression in the whole brain. Hatchlings with their nares blocked revealed neurons with c-fos expression above control levels principally in the c and d areas, while those subjected to magnetic field distortion had a wide spread activation of neurons throughout the brain predominantly in the dorsal ventricular ridge The present results support that Chelonia agassizi hatchlings use predominantly visual cues to orient their movements towards the sea. Olfactory and magnetic cues may also be use but their influence on hatchlings oriented motor behavior is not as clear as it is for vision. This conclusion is supported by the fact that in the absence of olfactory and magnetic cues, the brain turns on the expression of c- fos in neuronal groups that, in the intact hatchling, are not normally involved in accomplishing the task.
B41A-02
Preliminary results of high resolution magneto-biostratigraphy of continental sequences in Chapala Basin, Southwestern Mexico
Chapala Lake is south from Guadalajara, Jalisco State (Southwestern Mexico). Belongs to a series of Pliocenic lakes along the Mexican Volcanic Belt. It is localized in the Chapala rift, and the entire area is controlled by the tectonic setting of the Colima, Tepic and Chapala rifts, constituting the triple junction rift-rift-rift. The deposits studied belong to volcanosedimentary sequences, composed by lacustrine and fluvial associations alternated with units of ash and pumice. The faunistic component reported consists at least of 27 mammals species, and the sediments were there're in have to work with special attention for seek rodents by handpicking. Probably these rodents will be the clue to determine the deposits correlation. Core demagnetization shows that they are low-coercivity magnetic minerals like magnetite or Ti-magnetite. It was verified that the characteristic magnetization corresponds to MNRp and the inversion test resulted good. Rodents are represented by Geomynae, Sigmondontinae and Sciurinae. The Geomynae family is the most common, and the faunistic association indicates Blancan age. This also allows a correlation with the polarity pattern in the GSS between 3,6 and 2,6 Ma. Actually, is known that this kind of studies in continental sequences supported with paleontological record of vertebrates could give us a more precised calibration of the age of such deposits. Allowing better understanding of the evolution of these mammals and their path trough geological record. This work shows the preliminary results of rodents palaeontology and high resolution magneto-stratigraphy in the units from to Chapala Basin.
B41A-03
Magnetite-based magnetoreception: the effect of repeated pulsing on the orientation of migratory birds
Previous studies have shown that a magnetic pulse affected the orientation of passerine migrants for a short period only: for about 3 days, the birds' headings were deflected eastward from their migratory direction, followed by a phase of disorientation, with the birds returning to their normal migratory direction after about 10 days. To analyze the processes involved in the fading of the pulse effect, migratory birds were subjected to a second, identical pulse 16 days after the first pulse, when the effect of that pulse had disappeared. This second pulse affected the birds' behavior in a different way: it caused an increase in the scatter of the birds' headings for 2 days, after which the birds showed normal migratory orientation again. These observations are at variance with the hypothesis that the magnetite-based receptor had been fully restored, but also with the hypothesis that the input of this receptor was ignored. They rather indicate dynamic processes, which include changes in the affected receptor, but at the same time cause the birds to weigh and rate the altered input differently. The bearing of these findings on the question of whether single domains or superparamagnetic particles are involved in the magnetite-based receptors is discussed.
B41A-04
Preliminary characterization of iron-containing material and of neuronal assembles responsive to magnetic stimulation in the monarch butterfly (Danaus plexippus)
Migration is a common process among animal groups. Most of the biological events underlying migratory behavior are yet unknown. This is especially true for the neural mechanisms and the sensory information used by migratory species to define their routes. Hence, the present work aimed at demonstrating that the Monarch butterflies (Danaus plexippus) may use magnetic cues to define their route of migration by mapping neuronal assembles responsive to magnetic stimuli. Because research conducted in other insect species suggests that magnetite-based receptors may transduce the magnetic information into neuronal codes, we also evaluated the presence of magnetite in the body of the monarch butterfly. Our electron microscopy results demonstrate that the butterfly's head, abdomen and thorax contain iron particles of about 1-5 mm in diameter. Accordingly, Prussian blue histochemical techniques revealed the presence of abundant ferric deposits in diverse regions of the nervous system and the ventral abdomen. In contrast, the thoracic segments have only a few deposits. Finally, magneto metric measures concord with the morphological results. With regard to the mapping of the neuronal assembles responsive to magnetic stimuli, we were able to revealed c-fos immunoreactivity in groups of neurons located in the retina, lamina, lobula and deutero-cerebrum in butterflies subjected to magnetic stimuli. In sum, we believe that our results provide preliminary evidence supporting the existence of 1) a neural pathway capable of processing magnetic information in the monarch butterfly and 2) the presence of magnetite-like material in the various segments of its body.