Meeting Abstract
P2.31 Sunday, Jan. 5 15:30 Early evolution of molecular complexity in metazoans: an analysis of transcriptomes from all four sponge classes RIESGO, A; FARRAR, N; WINDSOR, PJ; GIRIBET, G; LEYS, SP*; Universitat de Barcelona; University of Alberta; University of Alberta; Harvard University; University of Alberta sleys@ualberta.ca
Sponges (Porifera) are among the earliest evolving metazoans. Their filter-feeding body plan and absence of conventional eumetazoan features suggest they diverged very early from other multicellular animals. Analyses of the Amphimedon sponge genome supports this view of uniqueness – many key metazoan genes are absent – but whether this is generally true of other sponges is unknown. We studied the transcriptomes of 8 sponge genera in 4 classes (Hexactinellida, Demospongiae, Homoscleromorpha and Calcarea) specifically seeking genes and pathways considered to be involved in animal complexity. For reference, we also sought these genes in transcriptomes and genomes of 3 unicellular opisthokonts and two bilaterian taxa. Our analysis showed that all sponge classes share an unexpectedly large complement of genes with other metazoans. Although some genera have more genes associated with bacteria, possibly explained by the large number of endosymbionts they possess, the complement of genes in other genera was more similar to that of bilaterians than other basally placed metazoans. We were surprised to find representatives of most molecules involved in cell-cell communication, signalling, complex epithelia, immune recognition and germ-lineage/sex, with only a few, but potentially key, absences. A noteworthy finding was that all demosponge transcriptomes generally showed evidence of loss of some important genes, which might reflect divergence from main-stem lineages including hexactinellids, calcareous sponges, and homoscleromorpha. In all, we conclude that the molecular complexity of sponges in all probability underpins a high level of physiological and morphological complexity.
