Evolution and ecology of antarctic sponges

• Main Author: Vargas Ramirez, Sergio
• Format: Thesis
• Language: English
• Published: Ludwig-Maximilians-Universität München 2012
• Subjects: Antarctica, Demospongiae, Hexactinellida, Sponges, Porifera, Ross Shelf, Weddell Sea; 500; 550; FOS Earth and related environmental sciences; Antarctic; Southern Ocean; Weddell Sea; Ross Sea; Weddell; Antarc*; Antarctica
• Online Access: https://dx.doi.org/10.5282/edoc.14126; https://edoc.ub.uni-muenchen.de/id/eprint/14126

Sponges are abundant and species-rich in Antarctic waters, and play important roles in the benthic ecosystems of the continent. The taxonomy of Antarctic sponges is, to some extent, well established, yet the phylogenetic relationships of this fauna remain unknown. Here, the first contributions to the knowledge of the evolution of Antarctic sponges are presented. A molecular phylogeny for the common Antarctic shelf glass sponge genus Rossella is provided. Based on nuclear and mitochondrial markers, it is shown that many of the species described for the genus, which usually are morphologically poorly defined and difficult to differentiate, likely, represent a single species (Rossella racovitzae) or a species complex. The deep Southern Ocean has yielded numerous, most likely new, species of the demosponge Familiy Cladorhizidae. Cladohizidae groups sponges largely known by their carnivorous habit, which is usually accompanied by the lack, or strong modification, of the sponge aquiferous system and by a distinct stipitate body shape. Cladorhizids are also important for the broader understanding of the phylogenetic relationships of the Order Poecilosclerida. In this study, the debated phylogenetic position of the genus Abyssocladia is clarified using recent collections of cladorhizid sponges and a (remarkable) new species of the genus Phelloderma (Phellodermidae) from the Southern Ocean, and partial sequences of the (nuclear) 28S rDNA and of the (mitochondrial) COI. The results show that Abyssocladia is a cladorhizid sponge and that Cladorhizidae is monophyletic, the consequences of these results for the prevalent interpretation of the evolution of poecilosclerid sponges are also discussed. The diversity of Antarctic sponges occurring on the shelf has been compared to that of tropical and subtropical ecosystems. Less is known about the sponge communities inhabiting the deeper waters of the Southern Ocean. The lack of information on deep benthic habitats, mainly due to the fact that sampling remote ecosystem such as Antarctica or the deep sea is expensive and technically difficult, hampers the determination of the number of species that inhabit the vast area of the deep Southern Ocean. In this work, estimation methods are used to predict lower bounds for the number of deep sea sponge species occurring in the Weddell Sea, Western Antarctica, and to show that the deep sea can be as rich as the shelf and that the total number of sponge species in Antarctica could be more than previously considered. Finally, a middle throughput DNA barcoding workflow for processing sponges was established and the performance of this analytical pipeline was analyzed based on a large collection (∼8300 specimens) of sponges from Australia avail- able for DNA barcoding. The barcoding workflow was also used to provide a comprehensive DNA-barcode database for the Ross Sea comprising ∼50 species of demosponges and covering ∼80% of the sponge species characteristic for this area. The generated barcode database was used to provide evidence for a long history of in situ evolution in Antarctic sponges, which is congruent with previous biogeographic hypotheses suggesting an ancient origin for Antarctic sponges.