Meeting Abstract

S8-2.2  Sunday, Jan. 6  The origin of freshwater sponges: when, where, and why? LAVROV, Dennis; Iowa State University

All animal phyla originated in the sea but only a few of them have colonized freshwater. The transition to limnic ecosystems required multiple adaptations to cope with highly variable temperatures, salinities, oxygen concentrations, and other parameters that make freshwater environments hostile to animal life. Consequently, freshwater animals typically represent only a few lineages within each phylum that made the transition from marine waters. Freshwater sponges are globally distributed and common members of limnic biotas. They are currently classified in the suborder Spongillina within the class Demospongiae. However their phylogenetic relationship to marine species and the time of their transition to freshwater environments remain controversial. The earliest freshwater sponge spicules are found from two disjoint time periods: from Permo-Carboniferous deposits of Europe and from Jurassic deposits of Europe and North America. It is unclear, however, whether the observed gap in the fossil record is a paleontological artefact or a reflection of two independent transitions to fresh water. Similarly, although freshwater sponges have been traditionally grouped with marine haplosclerids, several recent molecular phylogenetic studies reject this relationship. Here I use complete mitochondrial genome sequences from key representatives of demosponges to explore the phylogenetic position of freshwater sponges and to compare molecular and paleontological estimates for the time of their origin.