Speciation versus phenotypic plasticity in coral inhabiting barnacles: Darwin's observations in an ecological context

O. Mokady*, Y. Loya, Y. Achituv, E. Geffen, D. Graur, S. Rozenblatt, I. Brickner

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Speciation and phenotypic plasticity are two extreme strategic modes enabling a given taxon to populate a broad ecological niche. One of the organismal models which stimulated Darwin's ideas on speciation was the Cirripedia (barnacles), to which he dedicated a large monograph. In several cases, including the coral-inhabiting barnacle genera Savignium and Cantellius (formerly Pyrgoma and Creusia, respectively), Darwin assigned barnacle specimens to morphological 'varieties' (as opposed to species) within a genus. Despite having been the subject of taxonomic investigations and revisions ever since, the significance of these varieties has never been examined with respect to host-associated speciation processes. Here we provide evidence from molecular (12S mt rDNA sequences) and micromorphological (SEM) studies, suggesting that these closely related barnacle genera utilize opposite strategies for populating a suite of live- coral substrates. Cantellius demonstrates a relatively low genetic variability, despite inhabiting a wide range of corals. The species C. pallidus alone was found on three coral families, belonging to distinct higher-order classification units. In contrast, Savignium barnacles exhibit large between- and within-species variations with respect to both micromorphology and DNA sequences, with S. dentatum 'varieties' clustering phylogenetically according to their coral host species (all of which are members of a single family). Thus, whereas Savignium seems to have undergone intense host-associated speciation over a relatively narrow taxonomic range of hosts, Cantellius shows phenotypic plasticity over a much larger range. This dichotomy correlates with differences in life-history parameters between these barnacle taxa, including host-infestation characteristics, reproductive strategies, and larval trophic type.

Original languageEnglish
Pages (from-to)367-375
Number of pages9
JournalJournal of Molecular Evolution
Issue number3
StatePublished - 1999


  • 12S mt rDNA
  • Cantellius
  • Phenotypic plasticity
  • Phylogenetic reconstruction
  • Pyrgomatine barnacles
  • Savignium
  • Speciation


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