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Gastrotricha of Sweden - Biodiversity and Phylogeny
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0001-7151-5915
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Gastrotricha are small aquatic invertebrates with approximately 770 known species. The group has a cosmopolitan distribution and is currently classified into two orders, Chaetonotida and Macrodasyida. The gastrotrich fauna of Sweden is poorly known: a couple of years ago only 29 species had been reported. In Paper I, III, and IV, 5 freshwater species new to science are described. In total 56 species have been recorded for the first time in Sweden during the course of this thesis. Common species with a cosmopolitan distribution, e. g. Chaetonotus hystrix and Lepidodermella squamata, as well as rarer species, e. g. Haltidytes crassus, Ichthydium diacanthum and Stylochaeta scirtetica, are reported. In Paper II molecular data is used to infer phylogenetic relationships within the morphologically very diverse marine family Thaumastodermatidae (Macrodasyida). Results give high support for monophyly of Thaumastodermatidae and also the subfamilies Diplodasyinae and Thaumastoder­matinae. In Paper III the hypothesis of cryptic speciation is tested in widely distributed freshwater gastrotrichs. Heterolepidoderma ocellatum f. sphagnophilum is raised to species under the name H. acidophilum n. sp. The results indicate that L. squamata may be a complex of at least two species. In Paper III and V the phylogeny of Chaetonotidae (Chaetonotida), the largest family within Gastrotricha, is inferred. The group suffers from a troubled taxonomy and is hypothesized to be non-monophyletic. Results show that members of Dasydytidae are nested within the group. Since only 3 of 17 sampled genera are monophyletic, it is hypothesized that the cuticular structures used in current classification do not reflect phylogenetic relationships. The phylogenetic hypothesis generated in Paper V indicates a marine origin of the predominantly limnic Chaetonotidae with a subsequent secondary invasion to marine environments of some taxa.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University , 2011. , 34 p.
Keyword [en]
taxonomy, systematics, phylogeny, new species, cryptic species, Chaetonotidae, Dasydytidae, Thaumastodermatidae
National Category
Biological Systematics
Research subject
Systematic Zoology
Identifiers
URN: urn:nbn:se:su:diva-63590ISBN: 978-91-7447-397-1 (print)OAI: oai:DiVA.org:su-63590DiVA: diva2:451130
Public defence
2011-12-16, Lilla hörsalen, Naturhistoriska riksmuseet, Frescativägen 40, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Gastrotricha of Sweden
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Accepted. Paper 5: Manuscript.Available from: 2011-11-24 Created: 2011-10-24 Last updated: 2014-10-28Bibliographically approved
List of papers
1. One new species and records of Ichthydium Ehrenberg, 1830 (Gastrotricha: Chaetonotida) from Sweden with a key to the genus
Open this publication in new window or tab >>One new species and records of Ichthydium Ehrenberg, 1830 (Gastrotricha: Chaetonotida) from Sweden with a key to the genus
2009 (English)In: Zootaxa, ISSN 1175-5326, no 2278, 26-46 p.Article in journal (Refereed) Published
Abstract [en]

The freshwater gastrotrich fauna of Sweden is poorly known. Only seven species of freshwater gastrotrichs have been reported so far. This paper is the first in a series of contributions about the Swedish freshwater gastrotrich fauna. Here we describe one new species, Ichthydium skandicum n. sp., from Jamtland, northern Sweden. The new species falls within the boundary of the subgenus Forficulichthys and is morphologically closest to Ichthydium tanytrichum from which it can be differentiated based on the presence of four pairs of dorsal, keeled scales in the posterior trunk region. Moreover, we provide morphometric data for three additional Ichthydium species: I. diacanthum, I. squamigerum and I. tanytrichum, Italian species all of which are reported for the first time outside Italy. Considering the accompanying fauna, a total of thirteen freshwater Gastrotricha are reported for the first time from Sweden. Finally we present a dichotomous key for Ichthydium along with distributional data of the species considered.

Keyword
Chaetonotidae, Freshwater fauna, Meiofauna, Taxonomy, Taxonomical key
National Category
Zoology
Research subject
Systematic Zoology
Identifiers
urn:nbn:se:su:diva-33232 (URN)
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2014-10-28Bibliographically approved
2. Phylogeny of Thaumastodermatidae (Gastrotricha: Macrodasyida) Inferred from Nuclear and Mitochondrial Sequence Data
Open this publication in new window or tab >>Phylogeny of Thaumastodermatidae (Gastrotricha: Macrodasyida) Inferred from Nuclear and Mitochondrial Sequence Data
2011 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 3, e17892- p.Article in journal (Refereed) Published
Abstract [en]

Background

Phylogenetic relationships within Gastrotricha are poorly known. Attempts to shed light on this subject using morphological traits have led to hypotheses lacking satisfactory statistical support; it seemed therefore that a different approach was needed.

Methodology/Principal Findings

In this paper we attempt to elucidate the relationships within the taxonomically vast family Thaumastodermatidae (Macrodasyida) using molecular sequence data. The study includes representatives of all the extant genera of the family and for the first time uses a multi-gene approach to infer evolutionary liaisons within Gastrotricha. The final data set comprises sequences of three genes (18S, 28S rDNA and COI mtDNA) from 41 species, including 29 thaumastodermatids, 11 non-thaumastodermatid macrodasyidans and a single chaetonotidan. Molecular data was analyzed as a combined set of 3 genes and as individual genes, using Bayesian and maximum likelihood approaches. Two different outgroups were used: Xenotrichula intermedia (Chaetonotida) and members of the putative basal Dactylopodola (Macrodasyida). Thaumastodermatidae and all other sampled macrodasyidan families were found monophyletic except for Cephalodasyidae. Within Thaumastodermatidae Diplodasyinae and Thaumastodermatinae are monophyletic and so are most genera. Oregodasys turns out to be the most basal group within Thaumastodermatinae in analyses of the concatenated data set as well as in analyses of the nuclear genes. Thaumastoderma appears as the sister taxon to the remaining species. Surprisingly, Tetranchyroderma is non-monophyletic in our analyses as one group of species clusters with Ptychostomella while another appears as the sister group of Pseudostomella.

Conclusions/Significance

Results in general agree with the current classification; however, a revision of the more derived thaumastodermatid taxa seems necessary. We also found that the ostensible COI sequences from several species do not conform to the general invertebrate or any other published mitochondrial genetic code; they may be mitochondrially derived nuclear genes (numts), or one or more modifications of the mitochondrial genetic code within Gastrotricha.

National Category
Zoology
Research subject
Systematic Zoology
Identifiers
urn:nbn:se:su:diva-63236 (URN)10.1371/journal.pone.0017892 (DOI)
Projects
Gastrotricha of Sweden
Available from: 2011-10-12 Created: 2011-10-12 Last updated: 2017-12-08Bibliographically approved
3. A Phylogenetic approach to species delimitation in freshwater Gastrotricha from Sweden
Open this publication in new window or tab >>A Phylogenetic approach to species delimitation in freshwater Gastrotricha from Sweden
2012 (English)In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 683, no 1, 185-202 p.Article in journal (Refereed) Published
Abstract [en]

Gastrotricha is a cosmopolitan group of aquatic invertebrates. To date approximately 765 species have been described. This study is the first to deal with species delimitation and cryptic species of freshwater Gastrotricha. Three commonly encountered species, Heterolepidoderma ocellatum, Lepidochaetus zelinkai and Lepidodermella squamata, are investigated for cryptic speciation. Most of the material is based on Swedish specimens but closely related species from other parts of the world are also included. Taxonomic revisions are supported by phylogenies based on 18S rRNA, 28S rRNA and COI mtDNA of freshwater Chaetonotidae from several genera and inferred from Bayesian and maximum likelihood approaches. Heterolepidoderma ocellatum f. sphagnophilum is raised to species level, becoming H. acidophilum n. sp. Moreover, genetic data based on COI indicates high variation between two morphologically very similar groups of Lepidodermella squamata. The extent of cryptic speciation in L. zelinkai appears low. Based on the phylogenetic hypothesis presented in this paper the new species, Lepidodermella intermedia n. sp., from northernSweden is also described. The phylogenetic hypothesis generated show that Chaetonotidae is a non-monophyletic group.  

Keyword
Chaetonotidae, Freshwater fauna, Phylogeny, Taxonomic revisions, New species
National Category
Zoology
Research subject
Systematic Zoology
Identifiers
urn:nbn:se:su:diva-63237 (URN)10.1007/s10750-011-0956-1 (DOI)000299925200014 ()
Projects
Gastrotricha of Sweden
Available from: 2011-10-12 Created: 2011-10-12 Last updated: 2017-12-08Bibliographically approved
4. New species and new records of freshwater Chaetonotida (Gastrotricha) from Sweden
Open this publication in new window or tab >>New species and new records of freshwater Chaetonotida (Gastrotricha) from Sweden
2011 (English)In: Zootaxa, ISSN 1175-5326, E-ISSN 1175-5334, Vol. 3115, 29-55 p.Article in journal (Refereed) Published
Abstract [en]

Gastrotricha is a small phylum of acoelomatic aquatic invertebrates common in both marine and freshwater environments. The freshwater gastrotrich fauna of Sweden is poorly known and to date only twenty species have been reported. In this study two species of the genus Heterolepidoderma: Heterolepidoderma joermungandri n. sp. and H. trapezoidum n. sp. are described as new to science. Moreover nine species are presented as new to the Swedish fauna. Additional taxonomic information is also given for four species previously reported from the country. In total 7 genera spanning two families, Chaetonotidae and Dasydytidae, are presented and the number of reported freshwater gastrotrichs from the country is increased to 31.

Keyword
Chaetonotidae, Dasydytidae, Freshwater fauna, Taxonomy
National Category
Zoology
Research subject
Systematic Zoology
Identifiers
urn:nbn:se:su:diva-63238 (URN)
Projects
Gastrotricha of Sweden
Available from: 2011-10-12 Created: 2011-10-12 Last updated: 2017-12-08Bibliographically approved
5. Phylogeny of Chaetonotidae (Gastrotricha) inferred from nuclear and mitochondrial genes
Open this publication in new window or tab >>Phylogeny of Chaetonotidae (Gastrotricha) inferred from nuclear and mitochondrial genes
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Chaetonotidae is the largest family within Gastrotricha with almost 400 nominal species, represented in both freshwater and marine habitats. The group is probably non-monophyletic and suffers from a troubled taxonomy. Current classification is to a great extent based on shape and distribution of cuticular structures, characters that are highly variable. We present the most densely sampled molecular study so far where 17 out of 31 genera belonging to Chaetonotida are represented. Bayesian and maximum likelihood approaches based on 18S rDNA, 28S rDNA and COI mtDNA are used to reconstruct relationships within Chaetonotidae. The use of cuticular structures for supra-specific classification within the group is evaluated and the question of dispersal between marine and freshwater habitats is addressed. Moreover the subgeneric classification of Chaetonotus is tested in a phylogenetic context. Our results show high support for a clade containing Dasydytidae nested within Chaetonotidae. Within this clade only 3 genera are monophyletic following current classification. Genera containing both marine and freshwater species never form monophyletic clades and group with other species according to habitat. Marine members of Aspidiophorus appear to be the sister group of all other Chaetonotidae and Dasydytidae, indicating a marine origin of the clade. Halichaetonotus and marine Heterolepidoderma form a monophyletic group in a sister group relationship to freshwater species, pointing towards a secondary invasion to marine environments of these taxa. Our study shows the problems of current classification based on cuticular structures, characters that show homoplasy for deeper relationships.

Keyword
Paucitubulatina, Xenotrichulidae, Chaetonotus, Bayesian, Maximum likelihood, 18S rDNA, 28S rDNA, COI mtDNA
National Category
Zoology
Research subject
Systematic Zoology
Identifiers
urn:nbn:se:su:diva-63551 (URN)
Projects
Gastrotricha of Sweden
Available from: 2011-10-22 Created: 2011-10-22 Last updated: 2014-10-28Bibliographically approved

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