NICHOLS, Scott A.; Univ. of California, Berkeley: What molecules can do that morphology cannot: Sponge systematics.

Marine sponges are notorious for the extent of their conserved morphology. As a result of having few complex characters that can be used for systematics, species are frequently reported to have cosmopolitan distributions. The few data that we have regarding sponge life history and dispersal potential render hypotheses of cosmopolitanism improbable outside of specific instances of human-mediated dispersal. Because morphological characters often cannot resolve fine scale (e.g., species level) sponge phylogeny (or even distinguish O.T.U.’s in many cases), efforts to address many of the questions of interest to sponge ecologists and biologists hinge upon molecular systematic efforts alone. The search for informative molecular markers has recently revealed that the internal transcribed spacer regions (ITS) of the nuclear genome can resolve nodes that cannot be resolved using any known molecular markers of similar size. Here, I evaluate the effects of intra-genomic divergence of multiple-copy nuclear markers on phylogeny estimation and caution against the use of ITS without extensive taxonomic/geographic sampling in combination with the application of sub-cloning to detect intra-genomic divergence. Despite ontological and epistemological problems with using multi-copy nuclear markers, within an empirically sound framework they have the potential to finally shed light on the areas of sponge biology where morphology has failed.