Genetic diversity of selected petrosiid sponges

Sponges are simple animals that mostly inhabit the marine
ecosystem. The role of sponges in the marine ecosystem and the
potential of their bioactive compounds for the pharmaceutical
industry have already been reviewed. Because of the extensive
investigations of sponges within those two disciplines, marine
ecology and chemistry, sponges are among the best-studied Metazoa.
Likewise, sponges have been selected as animal models for
investigating the origin of the multicellularity because sponges
have a simple body structure and physiology (e.g., lack of nervous
and circulatory organs). Due to their diversity and abundance in
the tropics, particularly in the Indo-Pacific, sponges have also
attracted taxonomists, systematists and ecologists to assess their
diverseness and their phylogenetic and phylogeographic
relationships. Resolving those research questions is difficult,
because sponges are categorised as comparatively character poor
taxa. By using only conservative taxonomy or systematics, the
sponge diversity might therefore be underestimated. Inevitably,
sponge biologists have to employ molecular methods as additional
tools. In this research, molecular tools were used in order to
analyse the taxonomy, phylogeny and phylogeographic relationships
of selected sponge species. Xestospongia testudinaria &
Neopetrosia exigua (Family Petrosiidae, Order Haplosclerida) were
selected because of their conspicuousness in the Indo-Pacific coral
reef ecosystems, whereby Xestospongia testudinaria is prominently
known as the Indo-Pacific giant barrel sponge. Additionally, the
order Haplosclerida has been described as an example of sponge
order that has been examined systematically for a number of years
and displays major discrepancy between morphology and molecular
phylogenies. Molecular data suggests that the order needs revision
at all taxonomic levels, which is the cause for further conflicts
between taxonomists and systematists. In my research I focused
mostly on sponge samples that originated from South East Asia or
the Indo-Australian Archipelago (IAA). This region represents one
of the best-explored marine regions in the Indo-Pacific. The aim of
my research is to discover to what extent molecular tools are
suitable to detect a phylogenetic signal, a phylogeographical break
or a genotypic difference in the two selected sponge taxa. Several
markers from the mitochondrial (mtDNA), ribosomal (rRNA) and
nuclear (nucDNA) have been utilised. The 3' partition of the
cytochrome oxidase subunit 1 (I3-M11 of cox1) from the mtDNA could
be used to detect a genetic structure in Xestospongia testudinaria
in a geographical narrow scale study of < 200 km2 in Lembeh,
North Sulawesi, Indonesia (Chapter 6) and throughout the
Indo-Pacific despite limitations in the sample datasets (Chapter
2). In addition, the presence of a species complex in X.
testudinaria was detected with the aid of phylogenetic
reconstructions from a concatenation of mtDNA sequences (I3-M11 of
cox1 and the Adenosine Triphosphate Synthase F0 subunit 6 / ATP6),
and a nucDNA marker, the Adenosine Triphosphate Synthase β subunit
intron (ATPS-β intron) (Chapter 6). At the same time, the presence
of a species complex in X. testudinaria was recognised in a broader
scale study of the Indo-Australian Archipleago (IAA) (Chapter 3).
As a result, selected mtDNA and nucDNA markers in this thesis are
useful for the investigation of the taxonomical status and
phylogeographical relationships of X. testudinaria. A
phylogeographical break in the IAA region due to the Pleistocene
low sea level and Holocene recolonisation events (Chapter 3) could
not be recovered among X. testudinaria in a phylogeographical
analysis. Similarly, overlapping I3-M11 cox1 haplotypes between X.
testudinaria, X. muta and X. bergquistia were recovered. This might
be due to the presence of ancient polymorphisms on the barrel
sponge mtDNA markers. Molecular tools are also used to help
identifying my second selected sponge species (Chapter 4). The use
of selected cox2 mtDNA and 28S rRNA markers contributed
significantly to the identification of. Neopetrosia exigua used to
be a congeneric of X. testudinaria. During my examinations of
self-collected and holotype specimens I discovered that the species
named N. exigua bears a wrong name. For this reason, a taxonomical
revision is suggested and, more importantly, according to my
findings and the principle of priority in the ICZN (International
Code of Zoological Nomenclature) I use the species name
‘chaliniformis’ instead of the species name ‘exigua’. Furthermore,
the use of selected nucDNA marker, the Lysidyl Aminoacyl Transfer
RNA Synthetase (LTRS) intron, also contributes to the detection of
phylogeographical breaks in N. chaliniformis of the IAA (Chapter
5). In a nutshell, the success of unravelling sponge taxonomies,
phylogenies, and phylogeographic relationships always depends on
the suitability of the utilised molecular markers and the
significance of environmental influences on the sponges.
Haplosclerid sponges possess limited morphological features. These
hurdles create several problems, e.g. difficulties with taxa
delimitation and unresolved phylogeography relationships. Even
though the application of molecular techniques generated some
limitations and obstacles in these studies, it has already
contributed significantly to a better understanding of the
phylogenies, phylogeographic relationships and taxonomical problems
of X. testudinaria and N.chaliniformis, the species I selected for
my research.