Phylogeny

Evolution of Long-distance Migration

In general long-distance migration is viewed as a very plastic trait due to the rapid changes seen in migratory patterns. Many of the driving forces behind migration are ecological factors, each of which can act as a selective pressures on the evolution of long-distance migration.[1]  Many of the common ecological factors the drive long-distance migration was listed in Table 1.


Table 1. Factors affected the evolution and and ecology in long-distance migrants and their likely implications on migration. [1]

Evolution of Magnetic Orientation

Because the mechanisms of magnetic orientation and reception are just beginning to be uncovered, there is very little knowledge on the precise evolutionary path of the magnetoreception.  Some current opinions state that magnetoreception most likely evolved before the radiation of the animal phyla because due to the widespread distribution of organisms that use a magnetic sense.   Thus this hypothesis suggests that magnetic orientation is often taken to be an ancestral trait which did not evolve separately within groups. Kirschvink et al. believe that magnetoreception evolved through exaptation, an evolutionary process in which an ancilliary system of an organism begins to serve an adaptive role of which it was not originally selected for [9].



Evolution of Biogenic Magnetite

                                Typical octahedral bacterial magnetosomes seen through electron mircoscopy. [7, 8]      
  

Magnetite in bacteria in is found as a long chain which is surrounded by a phospohlipid bilayer, an organelle called the magnetosome.  There is a very deep fossil record of bacterial biogenic magnetite that goes back to about 2 million years ago. This evidence suggests that biogenic magnetite originated in bacteria and transfered to other organisms via endosymbiosis. [9,10]