The American Journal of Botany, Dec 1997 v84
n12 p1675(10)
The spatial genetic structure of
cytoplasmic (cpDNA) and nuclear (allozyme) markers within and among populations
of the gynodioecious Thymus vulgaris (Labiatae) in southern France. Michele Tarayre; Pierre
Saumitou-Laprade; Joel Cuguen; Denis Couvet; John D. Thompson.
Author's Abstract: COPYRIGHT 1997 Botanical Society of America, Inc.
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 [F.sub.ST] 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 [F.sub.ST] 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 ([F.sub.ST] =
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.
Key words: allozymes; cpDNA; gene flow; gynodioecy; Labiatae; population
structure; Thymus vulgaris.
