Taxophylogeny of calcareous sponges (TAXOCALC)

• Applicants: Dr. Oliver Voigt; Professor Dr. Gert Wörheide
• Subject Area: Systematics and Morphology (Zoology) ; Evolution, Anthropology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 559126114

Accurate species identification and a clearly defined phylogenetic classification are crucial for biological research, as they play a key role in ecological studies, ensure the reproducibility of laboratory experiments, and enable evolutionary questions to be asked. However, significant knowledge gaps persist in many marine taxa, such as sponges, which play crucial ecological roles in aquatic ecosystems from the deep sea to freshwater systems. Among those, calcareous sponges (Porifera, class Calcarea) are particularly challenging to grasp, as molecular phylogenies contradict morphology-based classifications, and many non-monophyletic taxa below the subclass level (orders, families, genera) have been proposed. Calcareous sponges show varying degrees of morphological complexity, especially regarding the organization of their aquiferous systems and the composition and arrangement of their skeletons. The evolution of these traits remains poorly understood. The gradual progression from simpler to more complex morphologies, which underlies traditional morphology-based classifications, fails to fully explain the differences in complexity. Phylogenetic analyses based on a limited number of genes have proven inadequate for fully resolving deeper evolutionary relationships and distinguishing between closely related species. The proposed project aims to close these knowledge gaps by first clarifying the deeper relationships among taxa, which is essential for necessary taxonomic revisions, and second tackling the complex challenge of species delimitation, especially for cryptic or polymorphic species. To achieve this, we will employ a cost-effective method using synthetic RNA baits to enrich and sequence ultraconserved element regions (UCE) and their more variable flanking regions from genomic libraries. This approach will enable us to obtain many phylogenetically informative loci from closely and distantly related species. The captured loci will be used to reconstruct a robust backbone phylogeny for calcareous sponges, which will serve as the foundation for understanding their morphological evolution. The project also aims to understand the role of secondary simplification and convergent evolution in shaping the observed complexity patterns of these traits in extant calcareous sponges.

• DFG Programme: Research Grants