The Evolutionary Theory along the Phylogenetic Tree of Eukaryotes after the Acquirement of Mitochondria

Abstract

According to the phylogeny of organisms reconstructed by the analyses on nucleotide base changes, the eukaryotes acquired the mitochondria first show the divergence of unicellular ones, then the divergence of fungi and sea algae occurs, and finally the animals and land plants appear from the unicellular eukaryotes other than fungi and sea algae.  The main purpose of the present paper is to resolve the problems how the animal and land plant have acquired many kinds of genes necessary for multicellularity and cell differentiation and they have shown explosive divergence afterward. First, it is proposed theoretically that the conjugation of unicellular monoploids to exchange homologous chromosomes yields the monoploid variant receiving more new genes generated from gene duplication than the monoploid having solely experienced gene duplication in a stepwise manner. Then, the evolutionarty line from such a cell differentiated monoploid to multicellular diploids is illustrated from a series of present-day green plants. Secondarily, a theoretical method for explaining the explosive divergence of morphological characters is proposed on basis of the breeding style of diploid eukaryotes. This method indicates that different combinational sets of new genes for cell differentiation arise from the successive hybridization of various silent variants with the latent variants yielded on the way to establish a new style diploid homologously when a new style diploid carrying a set of new genes heterogeneously appears under the high biological activity.  Such hybridization process continues until the fraction of silent variants is decreased in the original population. In contrast, the fungi and sea algae have directly attempted the multicellularity and cell differentiation in the diploid state but cannot accumulate the material and energy sufficient for further evolution of forming egg and seed, respectively. The landing of animals by metamorphosis is also discussed from the aspect of genome size and biological activity.