Schuster, A. (2017). Molecular paleobiology of 'lithistid' demosponges. Ludwig-Maximilians-Universität München. PhD thesis.

472856

10.5282/edoc.21655 [view]

Schuster, A.

2017

PhD thesis

Publication

https://edoc.ub.uni-muenchen.de/21655/

Available for editors   [request]

’Lithistid’ demosponges possess irregularly articulated siliceous spicules called desmas. They form polyphyletic sponge group regarded as pivotal among all Demospongiae as they display the richest and most continuous fossil record among the Class Demospongiae, reaching from the Cambrian to Recent. Therefore, ’lithistids’ present a promising group for investigat- ing demosponge divergence using a molecular paleobiological approach. However, to date, molecular phylogenetic studies including ’lithistids’ are scarce and their phylogenetic affini- ties to other demosponges as well as their classification is yet not completely understood. Most major ’lithistid’ assemblages are found in the deep-sea, on seamounts, steep slopes and caves, which challenge the sampling of those sponges. As a result many remote areas such as the Gal´apagos Archipelago or the Tropical Western Atlantic remain less investigated. In the context of a molecular paleobiological approach, this thesis contains eight Chapters on various aspects on the taxonomy, phylogeny and evolution of ’lithistid’ demosponges. The introductory chapter provides basic information on the current knowledge of Re- cent and fossil ’lithistid’ demosponges and the aims of this thesis. Chapter 2 provides the first comprehensive molecular and morphological investigation of ’lithistid’ demosponges, which sets the phylogenetic groundwork for the subsequent stud- ies. Embedded in a historical taxonomic overview on family and genus level, the formal reallocation of 8 out of 13 families to the order Astrophorina is proposed. Several fami- lies such as Corallistidae, Theonellidae and Phymatellidae were shown to be monophyletic, whereas Pleromidae and Scleritodermidae are polyphyletic. The polyphyletic Desmanthi- dae groups within Bubarida and Vetulinidae is confirmed to be sister to Spongillida and should be placed in its own order Sphaerocladina. Finally, we demonstrated that mega- and microscleres within ’lithistids’ possibly evolved and/or were lost several times independently. Chapter 3 reveals that the order Tetracinellida, including the ’lithistid’ family Scler- itodermidae, is a hotspot of mitochondrial group I introns. Analyzing the largest dataset on sponge mitochondrial group I introns (>95 specimens), we demonstrate that introns in sponges aggregate in the most conserved regions of COI, thus hamper its amplification. Fur- xxv thermore, horizontal and vertical gene transfer as well as secondary losses of introns are proven. Additionally, we confirm the possible fungal origin of most sponge group I introns. Chapters 4, 6 and 7 describe 11 species new to science using the phylogenetic and/or morphological species concept. In Chapter 4 we investigated the deep-water ’lithistid’ fauna of the Gal´apagos Archipelago provided descriptions of seven new species, most likely endemic to this remote marine area. In Chapter 6 and 7 new species of the genus Vetulina are described from the Caribbean, Indian Ocean and the Philippines indicating their high genetic similarity and disjunct distribution. The possible origin of Vetulina species in the Tethys Sea was tested using molecular clock analyses. Our dated phylogeny supports that Vetulina presents a relict fauna with its origin in the Tethys Sea. Chapter 5 presents the first dated phylogeny based on complete mitochondrial genomes of Demospongiae. The rich and continuous fossil record of ’lithistids’ were used for calibration and the fossilized birth-death clock model was applied. Results support a Neoproterozoic origin of Demospongiae, a divergence time estimation for the split of freshwater and marine sponges in the Carboniferous, and the possible divergence times of Tetractinellidae (~315 Ma), the Astrophorina (~240 Ma), the Spirophorina (~120 Ma) and the family Corallistidae (~188 Ma). Discrepancies of our dated phylogeny with their putative first fossil appearance dates were observed and discussed for each sponge group. Chapter 8 provides the currently largest molecular (249 specimens) and morphological (71 specimens) dataset on Tropical Western Atlantic ’lithistid’ demosponges. Our obtained phylogenies of COI and 28S provide novel insights into the phylogenetic relationships of TWA ’listhistids’, suggesting the revision of the higher-taxa relationships. Several new species, one new genus and one new suborder are proposed, including two new records from the TWA: Herengeria and Awhiowhio. On this groundwork the phylogenetic diversity and bathymetric distribution were analysed, demonstrating that Theonellidae and Corallistidae dominate the fauna, while Neopeltidae and Macandrewiidae are comparatively rare. Additionally, Theonel- lidae are more abundant in depths <300 m, while Corallistidae dominates deeper habitats >300 m. This dissertation contributes to a better understanding of the evolution of ’lithistid’ de- mosponges. It integrates for the first time both molecular, morphological as well as fossil data in a molecular paleobiological framework to answer pivotal questions on the phylogeny, taxonomy and evolution of this paleontologically immensely important demosponge group. This thesis forms the groundwork for many future investigations on ’lithistid’ demosponges enhancing the understanding of their evolution, divergence times and phylogeographic dis- tribution processes

Molecular systematics, Molecular biology
Paleontology, Fossils, Paleobiology
Systematics, Taxonomy

Porifera

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