Evolution and ecology of antarctic sponges

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.