Sponges (Porifera) are among the earliest evolving metazoans. Their filter-feeding body plan based on choanocyte chambers organized into a complex aquiferous system is so unique among metazoans that it either reflects an early divergence from other animals prior to the evolution of features such as muscles and nerves, or that sponges lost these characters. Sponges are host to a multitude of symbiont organisms that provides them with nutritional reserves or natural defensive products, which entail functional advantages in many habitats. Analyses of gene pathways involved in the establishment of a multicellular complex organism and the enabling of the symbiotic relationships gained through transcriptomic sequencing can shed light into the origins of metazoans.

Our analyses showed that all sponge classes share an unexpectedly large complement of genes with other metazoans. Interestingly, hexactinellid, calcareous, and homoscleromorph sponges share more genes with bilaterians than with nonbilaterian metazoans. We were surprised to find representatives of most molecules involved in cell–cell communication, signaling, complex epithelia, immune recognition, and germ-lineage/sex, with only a few, but potentially key, absences.Our results suggest that genetic complexity arose early in evolution as shown by the presence of these genes in most of the animal lineages, which suggests sponges either possess cryptic physiological and morphological complexity and/or have lost ancestral cell types or physiological processes. The transcriptomic approach to the recolonization of symbiont-deprived sponges enabled us to observe patterns of gene expression that may reflect biologically important interactions occurring between the symbiotic partners.

Ponente: Ana Riesgo, Postdoctoral Juan de la Cierva, Departamento de Biología Animal, Universitat de Barcelona

Presenta: Andrés Barbosa, Dpto. Biodiversidad y Biología Evolutiva. MNCN-CSIC

Producción y edición: Mediateca MNCN-CSIC.

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