Speciation Versus Phenotypic Plasticity in Coral Inhabiting Barnacles: Darwin's Observations in an Ecological Context |
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Authors: | O Mokady Y Loya Y Achituv E Geffen D Graur S Rozenblatt I Brickner |
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Institution: | (1) Institute for Nature Conservation Research, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel, IL;(2) Department of Zoology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel, IL;(3) Faculty of Life Sciences, Bar Ilan University, Ramat Gan 52900, Israel, IL;(4) Department of Molecular Microbiology and Biotechnology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel, IL |
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Abstract: | 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.
Received: 18 January 1999 / Accepted: 9 May 1999 |
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Keywords: | : Phylogenetic reconstruction — Speciation — Phenotypic plasticity — Pyrgomatine barnacles — Cantellius— Savignium— 12S mt rDNA |
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