Biomedical subjects

Alfonso F Davila

Publications and source records attributed to Alfonso F Davila.

3 recordsLinked to original sources

PubMed2006

Magnetic optimization in a multicellular magnetotactic organism.

Unicellular magnetotactic prokaryotes, which typically carry a natural remanent magnetic moment equal to the saturation magnetic moment, are the prime example of magnetically optimized organisms. We here report magnetic measurements on a multicellular magnetotactic prokaryote (MMP) consisting of 17 undifferentiated cells (mean from 148 MMPs) with chains of ferrimagnetic particles in each cell. To test if the chain polarities of each cell contribute coherently to the total magnetic moment of the MMP, we used a highly sensitive magnetization measurement technique (1 fAm(2)) that enabled us to determine the degree of magnetic optimization (DMO) of individual MMPs in vivo. We obtained DMO values consistently above 80%. Numerical modeling shows that the probability of reaching a DMO > 80% would be as low as 0.017 for 17 randomly oriented magnetic dipoles. We simulated different scenarios to test whether high DMOs are attainable by aggregation or self-organization of individual magnetic cells. None of the scenarios investigated is likely to yield consistently high DMOs in each generation of MMPs. The observed high DMO values require strong Darwinian selection and a sophisticated reproduction mechanism. We suggest a multicellular life cycle as the most plausible scenario for transmitting the high DMO from one generation to the next.

Cell Aggregation↗

PubMed2006

Mapping the sources of urban dust in a coastal environment by measuring magnetic parameters of Platanus hispanica leaves.

Tree leaves accumulate atmospheric particles on their surface, and a fraction of these particles exhibits magnetic properties that can be used to determine the spatial distribution of atmospheric dust in an urban area. This observation is exploited here to map sources of atmospheric pollutants in the coastal city of Vigo. The magnetic carriers on the leaves were iron oxide spherules (5-10 microm) and larger iron-bearing particles (typically 10-50 microm). The maximum values of magnetic remanence were very restricted in space and could be directly related to nearby polluting activities, such as road and railway traffic and shipyard and harbor activities; hence, our data represent main sources of urban dust in the city and not sinks. The concentrations of Fe, Zn, Ni, Pb, and Cu on the leaves showed a strong positive inter-correlation and also with the magnetic remanence of the leaves, suggesting common sources for these heavy metals and for the magnetic carriers. Mn and Cr did not show any significant correlation and their presence was linked to natural accumulations as micronutrients by the trees. The iron spherules and the heavy metal species identified here coincide with materials commonly found in sediments of the adjacent Ria de Vigo. The identification of the main sources of urban dust and heavy metals in the industrial and urban areas can, therefore, help in controlling these emissions to the Ria de Vigo.

Air Pollutants↗

PubMed2005

Magnetic pulse affects a putative magnetoreceptor mechanism.

Clusters of superparamagnetic (SP) magnetite crystals have recently been identified in free nerve endings in the upper-beak skin of homing pigeons and are interpreted as being part of a putative magnetoreceptor system. Motivated by these findings, we developed a physical model that accurately predicts the dynamics of interacting SP clusters in a magnetic field. The main predictions are: 1), under a magnetic field, a group of SP clusters self-assembles into a chain-like structure that behaves like a compass needle under slowly rotating fields; 2), in a frequently changing field as encountered by a moving bird, a stacked chain is a structurally more stable configuration than a single chain; 3), chain-like structures of SP clusters disrupt under strong fields applied at oblique angles; and 4), reassemble on a timescale of hours to days (assuming a viscosity of the cell plasma eta approximately 1 P). Our results offer a novel mechanism for magnetic field perception and are in agreement with the response of birds observed after magnetic-pulse treatments, which have been conducted in the past to specifically test if ferrimagnetic material is involved in magnetoreception, but which have defied explanation so far. Our theoretical results are supported by experiments on a technical SP model system using a high-speed camera. We also offer new predictions that can be tested experimentally.

Animals↗