Marine Biology

, Volume 151, Issue 6, pp 2183–2193 | Cite as

Cryptic speciation in the recently discovered American cycliophoran Symbion americanus; genetic structure and population expansion

  • Jessica M. Baker
  • Peter Funch
  • Gonzalo GiribetEmail author
Research Article


Symbion americanus was recently described as the second species in the phylum Cycliophora, living commensally on the American commercial lobster Homarus americanus. A previous genetic analysis of American and European populations of cycliophorans suggested that haplotype divergence in S. americanus was much greater than in its European counterpart S. pandora. This study examined the population structure and demographics of 169 individuals thought to belong to S. americanus collected from lobsters over 13 North American localities (Nova Scotia, Canada to Maryland, USA) between October 2003 and January 2006. Cytochrome c oxidase subunit I sequence data clearly suggested the presence of three cryptic lineages in a species complex, often co-occurring in the same lobster specimens. One of these lineages, named the “G” lineage, was represented by very few individuals and therefore was excluded from subsequent statistical analyses. The other two sympatric lineages, named the “T” and “C” lineages, showed different population structure and demography. Although limited geographic structure was found in the T lineage, the C lineage showed higher nucleotide and haplotype diversity values, as well as more variation between localities. The data also indicated that the T lineage underwent a recent population expansion, suggesting that the C and T lineages may have speciated in allopatry but a subsequent population expansion may have been responsible for their current sympatric distribution. Studies on the anatomy and ecology of the sympatric lineages of this species complex should provide further information on the identity of the holotype of S. americanus, which currently cannot be ascribed to any of the three cryptic lineages.


Mismatch Distribution GeneAmp Polymerase Chain Reaction System Dwarf Male Recent Population Expansion Cryptic Lineage 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We are indebted to Matthias Obst for his continuous advice and support, which made this study possible. Financial support for this study was provided by the Danish Research Agency (contract grant no. 21-02-0455 to P.F. and G.G.) and by internal funds from the Museum of Comparative Zoology, Harvard University. Three anonymous reviewers provided comments that helped to improve this study.


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Jessica M. Baker
    • 1
  • Peter Funch
    • 2
  • Gonzalo Giribet
    • 1
    Email author
  1. 1.Department of Organismic and Evolutionary Biology, Museum of Comparative ZoologyHarvard UniversityCambridgeUSA
  2. 2.Department of Ecology and Genetics, Institute of Biological SciencesUniversity of AarhusAarhus CDenmark

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