Fig. 5: Gene expression across Ephydatia muelleri development.

Heatmap shows relative expression of differentially expressed genes (scale at right of heatmap) across the course of E. muelleri development, with triplicate samples for Stages 1–3 and 5 of growth. Note the large changes in gene expression that occur between Stages 1 and 2, and between Stages 3 and 5. These changes in expression are coincident with the occurrence of a silica-based skeleton (beginning Stage 2) and a fully formed aquiferous system including an osculum (Stage 5). Also shown on this figure are the GO terms matched by these genes (categories at right of heatmap) and the origin point of these genes—whether they are sponge/Ephydatia novelties, or found more generally across the animal tree of life. E. muelleri specific genes are found more commonly in Stage 1, likely a result of the specialist needs of the gemmule stage tissue represented by this sample. Images at right are of (top: bottom) a Stage 1 gemmule, taken with an SEM/light microscope (inset), a Stage 3 hatching sponge, showing the occurrence of spicules (see image top right, labelled with silicatein in green), and a Stage 5 juvenile sponge, with a well-developed aquiferous system (inset shows choanocyte chambers with collars labelled red for actin, flagella green for tubulin and nuclei, blue). Scale bars: top 100 µm, middle 50 µm, and bottom 10 µm. In these images only one replicate is shown for illustrative purposes, but in all cases the number of individual gemmules or sponges observed with these patterns was >10, for >3 replicates. Source data are provided as a Source Data file.