Exploring the species boundaries in terrestrial clitellates (Annelida: Clitellata)
Abstract
The biological diversity in the soil is much higher than most people can imagine, and a very important group of animals living there are earthworms and other clitellate worms. It has been found that several clitellate morphospecies are in fact complexes of so called cryptic species, and the number of species in this group may be much higher than previously believed. In this thesis, I explore the species boundaries of terrestrial clitellates by combining various data sources and methods as a basis for taxonomical decisions. A widely used approach for studying cryptic species is DNA-barcoding, where a single standardised marker is used for the identification of organisms and discovering new species. For animals, the marker generally used is the mitochondrial COI gene.
In the thesis, I present four different cases, from three different clitellate families: 1) A variety of Rhyacodrilus falciformis was shown to be a distinct species, whereas other COI clusters were found to be part of the same species. 2) Extensive cryptic diversity was found in the genus previously known as Cognettia, a group that includes C. sphagnetorum, a well-studied model in soil biology. This taxon and C. glandulosus were both found to be complexes of cryptic species. The generic taxonomy of Cognettia was revised and the genus split into its two senior synonyms, Euenchytraeus and Chamaedrilus, and the species in the C. sphagnetorum complex were revised and described. 3) In the earthworm Aporrectodea longa, two well separated COI lineages were found to be part of the same species. 4) In the earthworm genus Lumbricus, the previously noted split between L. terrestris and L. herculeus was verified using nuclear data, and in the morphospecies L. rubellus seven cryptic species were found. The first evidence of limited hybridisation within the genus was also found, between L. terrestris and L. herculeus, as well as and between species within L. rubellus s.lat.
To conclude, I have shown that the species diversity among terrestrial clitellates is larger than previously known based on morphology, and that species can be robustly delimited using a combination of mitochondrial and nuclear markers, supported with morphology. I have also found that using DNA-barcoding alone will often overestimate the number of clitellate species, and caution is required when using it.
Parts of work
I. Martinsson, S., Achurra, A., Svensson, M. & Erséus C. (2013). Integrative taxonomy of the freshwater worm Rhyacodrilus falciformis s.l. (Clitellata: Naididae), with the description of a new species. Zoologica Scripta, 42(6), 612–622. ::doi::10.1111/zsc.12032 II. Martinsson, S. & Erséus, C. (2015). Cryptic diversity in the well-studied terrestrial worm Cognettia sphagnetorum (Clitellata: Enchytraeidae). Pedobiologia, 57(1), 27-35. ::doi::10.1016/j.pedobi.2013.09.006 III. Martinsson, S., Rota, E. & Erséus, C. (2014). Revision of Cognettia (Clitellata, Enchytraeidae): re-establishment of Chamaedrilus and description of cryptic species in the sphagnetorum complex. Systematics and Biodiversity, 13(3), 257-277. ::doi::10.1080/14772000.2014.986555 IV. Martinsson, S., Rhodén, C. & Erséus, C. (2015). Barcoding gap, but no support for cryptic speciation in the earthworm Aporrectodea longa (Clitellata: Lumbricidae). Mitochondrial DNA, 1-9. ::doi::10.3109/19401736.2015.1115487 V. Martinsson, S., & Erséus, C. (2017) Cryptic speciation and limited hybridization within Lumbricus earthworms (Clitellata: Lumbricidae). Molecular Phylogenetics and Evolution, 106, 18-27. ::doi::10.1016/j.ympev.2016.09.011
Degree
Doctor of Philosophy
University
University of Gothenburg. Faculty of Science
Institution
Department of Biological and Environmental Sciences ; Institutionen för biologi och miljövetenskap
Disputation
Fredagen den 18 november 2016 kl. 10.00, Hörsalen, Zoologen, Medicinaregatan 18A
Date of defence
2016-11-18
svante.martinsson@bioenv.gu.se
Date
2016-10-26Author
Martinsson, Svante
Keywords
Oligochaeta
species delimitation
Clitellata
Annelida
DNA-barcoding
cryptic species
Enchytraeidae
Lumbricidae
Naididae
Publication type
Doctoral thesis
ISBN
978-91-628-9987-5
978-91-628-9988-2
Language
eng