W�RHEIDE, G; SOL�-CAVA, A M; GZG Geobiology, Univ. of G�ttingen, Germany; Inst. Biologia, Univ. Fed. Rio de Janeiro, Brazil: What do genetic markers tell about sponge populations that we do not already know?

Molecular markers have transformed our understanding of processes acting at the population level in marine invertebrates, including sponges. Due to the high level of morphological conservativeness over wide geographic distances, panmixia of sponge populations was assumed. However, allozyme studies of over 60 sponge species demonstrated that morphologically very similar allopatric populations almost invariably belonged to different species. Hence, cosmopolitanism in sponges is likely to be very rare, which has resulted in a profound change in modern sponge taxonomy. The application of DNA markers allowed for a shift towards more genealogical approaches, but mtDNA, most commonly used in other taxa, seems to be too conserved in sponges to be useful at the population level. CO1 sequences in populations of the demosponge Astrosclera willeyana, for example, are nearly invariant between Red Sea and Central Pacific. Up to now, most population-level analyses in sponges have concentrated on the rDNA internal transcribed spacers (ITS), which seem to provide good resolution at larger spatial scales. For example, analyses of ITS sequences have allowed inferences about historical and ecological factors shaping present day distributions of the Indo-Pacific coral reef calcareous sponge Leucetta chagosensis. However, because of the risk of paralogy, levels of intragenomic variation in the ITS multi-copy array must be investigated before it can be routinely used in phylogeographic studies. Additional markers such as microsatellites or single-copy nDNA markers (e.g. Introns) are only beginning to emerge. The application of such markers may provide data of higher resolution to improve our understanding of sponge genetics and phylogeography.