The spatial genetic structure of cytoplasmic (cpDNA) and nuclear (allozyme) markers within and among populations of the gynodioecious Thymus vulgaris (Labiatae) in southern France |
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Authors: | Tarayre M Saumitou-Laprade P Cuguen J Couvet D Thompson J |
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Affiliation: | 1. Centre d'Ecologie Fonctionnelle et Evolutive, CNRS, Route de Mende, BP 5051, F-34033 Montpellier Cedex, France;2. Génétique et Evolution des Populations Végétales, URA CNRS 1185, Université de Lille I, Bât. SN2, F-59655 Villeneuve d'Ascq Cedex, France;3. Université Paris VI - URA CNRS 258, Institut d'Ecologie, Bât. A, 7 quai St Bernard, F-75252 Paris Cedex 05, France |
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Abstract: | Recent advances in molecular biology have allowed the development of techniques to contrast spatial differentiation in nuclear and cytoplasmic genes and thus provide important data on relative levels of gene flow by pollen and seed in higher plants. In this paper, we compare the spatial structure of nuclear (allozymes) and cytoplasmic (cpDNA) genes among populations of the gynodioecious Thymus vulgaris in southern France. Based on a combination of three restriction enzymes (CfoI, EcoRV, and PstI), eight chlorotypes (combination of three restriction enzyme patterns revealed by Southern hybridization of Beta vulgaris cpDNA) were identified in the 13 studied populations. One chlorotype was particularly abundant and was detected in nearly all populations. Only one chlorotype was specific to a single population. Up to four different chlorotypes were observed in some populations. An FST of 0.238 (P < 0.002) for cpDNA haplotypes indicates spatial structure of cytoplasmic genes among the studied populations. Similar patterns were found within a single young population (CAB) structured in patches and surrounded by a continuous cover of T. vulgaris where the FST is 0.546 (P < 0.002). No significant correlation between sex and chlorotype nor between cpDNA diversity and female frequency was detected. Allozyme markers showed markedly less spatial structure (FST = 0.021 among populations and 0.019 in the CAB population, P < 0.001). This difference between cpDNA and nuclear allozyme markers suggests that pollen dispersal is more important than seed dispersal both among and within populations. |
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Keywords: | allozymes cpDNA gene flow gynodioecy Labiatae population structure Thymus vulgaris |
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