Can Molecular Techniques Change Our Ideas About the Species Concept?

  • Linda K. Medlin
  • Martin Lange
  • Gary L. A. Barker
  • Paul K. Hayes
Part of the NATO ASI Series book series (volume 38)


Molecular techniques can now be used to address many important questions concerning taxonomic affinity, genetic diversity, gene flow and dispersal. These data (protein or nucleic acid sequence information) can augment our understanding of a species in the marine environment. There is growing evidence that speciation and dispersal mechanisms in the marine environment are very different from terrestrial systems and occur at different rates. We have examined species/genetic diversity in three ecologically important members of the marine phytoplankton: the prymnesiophytes Phaeocystis and Emiliania huxleyi and the diatom Skeletonema costatum. All are high dispersal taxa. Differences among Phaeocystis species as measured by 18S rDNA sequence comparison indicate that extant Phaeocystis species probably arose from a cosmopolitan warm-water ancestor. Speciation events in this genus appear to have responded to major global cooling events. Two species complexes are apparent: one corresponds to taxa from polar regions and the other to taxa from temperate to tropical regions. Emiliania huxleyi, a much younger species, has dispersed across many océanographie barriers during much colder climatic conditions. Sequence data from coding and non-coding regions confirm that it is a single taxon, but RAPD techniques reveal extensive genetic diversity with both spatial and short-term temporal resolution. Sequence comparison of isolates of Skeletonema costatum, a cosmopolitan neritic form, reveals at least one cryptic species, which can also be differentiated by certain morphological features, and a cluster of isolates that may be sibling species. It may be that in many planktonic forms molecular speciation has proceeded, whereas morphological divergence has not. The abundance of sibling species in the marine environment is only now being revealed (Knowlton 1993). The fitness of form resulting in similar if not identical morphotypes has analogies at all taxonomic levels in the sea (Knowlton 1993, Sournia 1988).


Sibling Species Species Concept Skeletonema Costatum Emiliania Huxleyi Crypthecodinium Cohnii 
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Copyright information

© Springer-Verlag Berlin Heidelberg 1995

Authors and Affiliations

  • Linda K. Medlin
    • 1
  • Martin Lange
    • 1
  • Gary L. A. Barker
    • 2
  • Paul K. Hayes
    • 2
  1. 1.Alfred-Wegener-InstituteBremerhavenGermany
  2. 2.School of Biological SciencesUniversity of BristolBristolUK

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