ISSN 10227954, Russian Journal of Genetics, 2013, Vol. 49, No. 8, pp. 839–846. © Pleiades Publishing, Inc., 2013.
Original Russian Text © V.B. Itskovich, O.V. Kaluzhnaya, S.I. Belikov, 2013, published in Genetika, 2013, Vol. 49, No. 8, pp. 966–974.
839
INTRODUCTION
Sponges (Porifera) are the most ancient and prim
itive metazoans aged about 580 million years [1].
Sponges are characterized by considerable biodiversity
(about 7000 species have been described). They live in
seawater and fresh water from the tropics to Antarctica
[2]. Due to their ability to bioaccumulate, sponges are
indicators of the state of the environment. In addition,
sponges are the source of a great number of biologi
cally active compounds, that makes the development
of correct taxonomy of this group quite timing.
Freshwater sponges (order Haplosclerida, suborder
Spongillina) include about 200 species [3]. The taxon
omy of sponges is based on the specific structure of
their skeletal elements, spicules, which are greatly
variable in morphology. In unfavorable environmental
conditions cosmopolitan freshwater sponges can form
gemmules. The structure of gemmules and gemmo
scleres is the important diagnostic criterion. More
over, endemic sponge genera, which inhabit ancient
lakes, lose the ability to form gemmules due to con
stant living conditions.
Baikal sponges (Lubomirskiidae and Spongillidae
families) are important components of the littoral eco
systems of the lake. The endemic Lubomirskiidae
family is represented by a complex of closely related
species and is a unique object for studying evolution at
the molecular level. According to the existing system
atics, Lake Baikal is inhabited by 12 species and 2 sub
species of the Lubomirskiidae family [4, 5]. The tax
onomy of this family is complicated, and phylogenetic
relationships among the species are not resolved. The
species of this family do not form gemmules, and their
systematics is based on the limited number of morpho
logical characters, including the form and lengths of
megascleres, and skeletal characteristics. A recent
revision of the systematics of the family allowed to
describe the new species. However, in the collections,
there are the samples with unclear taxonomic position
[5, 6].
Molecular methods are successfully applied to the
phylogenetic analysis of freshwater sponges [7–11].
Based on an analysis of the 18S rRNA and
COXI
genes,
it was demonstrated that endemic genera from ancient
lakes originated from several founder species. More
over, the Spongillidae family is paraphyletic relative to
Lubomirskiidae [8]. The molecular phylogenetic anal
ysis of freshwater sponges indicated the insufficient
variability of the 18S rRNA and
COXI
genes for the
analysis of closely related species. An analysis of the
rRNA internal transcribed spacers, ITS1 and ITS2,
showed that the endemic Lubomirskiidae family was
monopyletic and originated from the spongillids rela
tive to
Ephydatia muelleri
[9]. Furthermore, genetic
distances between the Baikal species were low, and the
distribution of the species into genera was not sup
ported. These data indicate the need for the taxonomic
revision of Lubomirskiidae.
Correct phylogenetic reconstructions require the
use of a set of nuclear and mtDNA markers with dif
ferent rates of evolution. Since introns and intergenic
regions are characterized by considerably higher rates
of mutation fixation and their use as molecular taxo
Investigation of Nuclear and Mitochondrial DNA Polymorphism
in Closely Related Species of Endemic Baikal Sponges
V. B. Itskovich, O. V. Kaluzhnaya, and S. I. Belikov
Limnological Institute, Siberian Branch of the Russian Academy of Sciences, Irkutsk, 664033 Russia
email: itskovich@mail.ru
Received September 11, 2012
Abstract
—In order to investigate the phylogenetic relationships among endemic Baikal sponges of the family
Lubomirskiidae and to clarify their taxonomy, the sequence variation at the silicateinencoding gene and the
mtDNA intergenic region was examined. Phylogenetic analysis of the silicatein
α
1 gene exonic regions in six
freshwater sponge species revealed considerable interspecific variability of this region. The analysis performed
did not support the monophyly of the genera
Lubomirskia
and
Baikalospongia
. The mtDNA region between
the
COX2
and
ATP6
genes was examined in five species from the Lubomirskiidae family, including multiple
samples for analyzing intraspecific variations. According to the data obtained, the genus
Baikalospongia
was
paraphyletic with respect to
Lubomirskia
, while
B. bacilifera
and
B. recta
did not form monophyletic groups.
Molecular data indicate that taxonomy of Lubomirskiidae should be revised. It was demonstrated that, in
endemic Baikal sponges, the accelerated evolution was accompanied by an increase in the length of the non
coding regions in both mitochondrial and nuclear genes.
DOI: 10.1134/S1022795413080036
ANIMAL GENETICS
@Phil_Robichaud
@deepthiw
@JoseServera