Evolution of size and pattern in the social amoebas.
Bottom Line: The foundation is a recently constructed molecular phylogeny of the Dictyostelia, which was used to examine trends in the evolution of novel forms and in the divergence of genes that shape these forms.The role of cAMP in aggregation arose through co-option of a pathway that originally acted to coordinate fruiting body formation.The genotypic changes that caused this innovation and the role of dynamic cAMP signaling in defining fruiting body size and pattern throughout social amoeba evolution are discussed.
Affiliation: College of Life Sciences, University of Dundee, MSI/WTB/JBC complex, Dow Street, Dundee DD1 5EH, UK. email@example.comShow MeSH
Mentions: Comparison of conserved DNA or protein sequences is a more direct and reliable method to establish genetic relationships. Two family trees of the social amoebas were constructed by comparing the DNA sequences of their small subunit ribosomal RNA (SSU rRNA) gene on one hand and the amino-acid sequences of their α-tubulin protein on the other. Both trees show that the similarities in fruiting body architecture only partially reflect an underlying genetic similarity.24 Instead, both the α-tubulin tree and the SSU rRNA tree shown here (Fig. 3) subdivide the 75 known species of social amoebas into four major groups. There are dictyostelids in all four groups. The acytostelids and all white polysphondylids are members of group 2, but the purple polysphondylid P. violaceum occupies a position between groups 3 and 4, and forms a small clade with the dictyostelid D. laterosorum. This indicates that at least two out of the three previously proposed genera are polyphyletic. Multiple origins for the polyspondylids were also predicted by a family tree that was based on 18 combined morphological traits.29
Affiliation: College of Life Sciences, University of Dundee, MSI/WTB/JBC complex, Dow Street, Dundee DD1 5EH, UK. firstname.lastname@example.org