Two cryptic species of the Hediste diversicolor group (Polychaeta, Nereididae) in the Baltic Sea, with mitochondrial signatures of different population histories
A presence of two cryptic biological species of Hediste diversicolor complex polychaetes was corroborated in a geographical survey of some 30 populations from the eastern and southern coasts of the Baltic Sea, with data from four completely diagnostic allozyme characters. Species A was dominant in the northernmost part of the Baltic Hediste range (Bothnian Sea), whereas Species B alone was found in the south (Poland, Germany, Denmark). In the intervening region, comprising the majority of the sites studied in southern Finland and Estonia, the two species were usually found together, with no evidence of recent hybridisation (i.e., no heterozygote genotypes). While mitochondrial DNA also distinguished the two taxa, it was not similarly completely diagnostic, but there were rare cases (ca 5%) of lineage mismatch indicating that some introgression has occurred in the past. Comparison with published data suggests that species A also inhabits the North Sea–NE Atlantic–Mediterranean coasts, and species B is also present in the North Sea and the NW Atlantic (Canada). Within the Baltic, the two species show distinctly different patterns of mtDNA diversity, plausibly related to different colonisation histories. Species A shows a generally high haplotype and nucleotide diversity, whereas in species B we found only four deeply diverged groups of closely related haplotypes. Hypothetically this could indicate a recent expansion of species B from a small number of colonising individuals. Moreover, species B showed marked intraspecific geographical structuring, with co-incident genetic changes along the N Estonian–S Finnish coasts both in mtDNA and an allozyme marker; this pattern suggests a contact between two genetically distinct invasion waves of different origins. In all, species A and B represent good, reproductively isolated and partly sympatric species which require to be recognised in ecological work. A formal taxonomical description is needed, but awaits better, range-wide distributional and ecological characterisation and working out of morphological differences that enable a practical identification.
KeywordsCryptic Species Incongruence Length Difference Mitochondrial Introgression Invasion Wave Strong Geographic Structure
We thank all those who kindly sent us samples or helped in the field, including D. Daunys, M. Daneliya, J. Kotta, R. Nikula and M. Reinikainen. Special thanks to S. Nielsen for help with most of the sampling, even after losing his car to thieves (hence the absence of frozen samples from Latvia). We also thank three anonymous referees for insightful comments. The study has been supported by grants from the Walter and Andrée de Nottbeck Foundation and the University of Helsinki research funds.
- Audzijonytė A, Väinölä R (2005) Diversity and distributions of circumpolar fresh- and brackish-water Mysis (Crustacea: Mysida): descriptions of M. relicta Lovén, 1862, M. salemaai n. sp., M. segerstralei n. sp. and M. diluviana n. sp., based on molecular and morphological characters. Hydrobiologia 544:89–141. doi: 10.1007/s10750-004-8337-7 CrossRefGoogle Scholar
- Avise JC (2000) Phylogeography. Harvard University Press, CambridgeGoogle Scholar
- Blank M, Laine AO, Jürss K, Bastrop R (2008) Molecular species identification key based on PCR/RFLP for discrimination of three polychaete sibling species of the genus Marenzelleria, and their current distribution in the Baltic Sea. Helgol Mar Res 62:129–141. doi: 10.1007/s10152-007-0081-8 CrossRefGoogle Scholar
- Folmer O, Black M, Hoen W, Lutz R, Vrijenhoek R (1994) DNA primers for amplification of mitochondrial cytochrome c oxidase subunit I from diverse metazoan invertebrates. Mol Mar Biol Biotechnol 3:294–299Google Scholar
- Hall TA (1999) Bioedit: a user-friendly biological sequence alignment editor and analysis program for Windows 95/98/NT. Nucleic Acids Symp Ser 41:95–98Google Scholar
- Murphy RW, Sites JW, Buth DG Jr, Haufler CH (1996) Proteins: isozyme electrophoresis. In: Hillis DM, Moritz C, Mable BK (eds) Molecular systematics, 2nd edn, Sinauer Associates, Sunderland, MA, pp 51–120Google Scholar
- Nei M (1987) Molecular evolutionary genetics. Columbia University Press, New YorkGoogle Scholar
- Swofford DL (2003) PAUP*. Phylogenetic analysis using parsimony (*and other methods), Version 4. Sinauer Associates, Sunderland, MAGoogle Scholar
- Thorpe JP (1983) Enzyme variation, genetic distance and evolutionary divergence in relation to levels of taxonomic separation. In: Oxford GS, Rollison D (eds) Protein polymorphism: adaptive and taxonomic siginificance. Academic Press, London, pp 131–152Google Scholar
- Väinölä R (1986) Sibling species and phylogenetic relationships of Mysis relicta (Crustacea: Mysidacea). Ann Zool Fenn 23:207–221Google Scholar