Conservation of morphology and gene expression patterns in the developmental programs of D. discoideum and D. purpureum. (a) An illustration of the developmental programs. Both species begin the developmental program by aggregation of starving cells into centers that contain approximately 50,000 cells. The aggregates undergo morphological transformations from loose aggregates to tight aggregates to tipped aggregates while the cells differentiate into prespore and prestalk cells (not shown). Later in development, D. purpureum slugs (right) migrate while leaving a cellular stalk behind them whereas D. discoideum slugs do not. After culmination, the fruiting bodies are similar in size and shape and both consist of a ball of spores (sorus) carried on top of a cellular stalk as indicated. They differ in that D. purpureum fruiting bodies lack a basal disc at the bottom of the stalk and their sori are purple rather than yellow. (b) Developmental morphologies. A top view with light microscopy of cells developing on dark nitrocellulose filters is shown. Species names and developmental times are indicated. Scale bar: 0.5 mm. (c) The heat maps represent the patterns of change in standardized mRNA abundance for all the genes in the D. discoideum and the D. purpureum genomes. Each row represents an average of 85 genes and each column represents a developmental time point (hours). The colors represent relative mRNA abundances (see scale). The genes are ordered according to their regulation pattern in each species. The black lines divide the transcripts, from top to bottom, into: down-regulated, intermediate regulation and up-regulated. The dendrograms represent the differences between the transcriptomes at each time point. (d) The maximal similarity between each D. purpureum developmental time point (x-axis) to each D. discoideum time point (y-axis) across the 7,560 orthologs. The dashed line represents a hypothetical comparison between perfectly synchronous developmental programs.