Genetic Diversity and Structure of Wild Tunisian Myrtus communis L. (Myrtaceae) Populations |
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Authors: | Chokri Messaoud Mohamed Laarbi Khoudja Mohamed Boussaid |
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Institution: | (1) National Institute of Applied Sciences and Technology (INSAT) Department of Biology, Laboratory of Plant Biotechnology Centre Urbain Nord, BP. 676, 1080 Tunis Cedex, Tunisia;(2) National Institute of Research in Genie Rural, Water and Forests (INRGREF), BP. 10, Ariana, 2080, Tunisia |
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Abstract: | Myrtus communis L. (Myrtaceae), in Tunisia, is closely associated with Quercus suber L. forest which stretched continuously from the North to parts of Cap Bon and Tunisian Dorsal. The destruction of the primary
oak forests associated to an over-exploitation of Myrtus for its essential oil quality had led to discontinuous populations exhibiting various levels of degradation. Using starch
gel electrophoresis, we analyzed the polymorphism of nine isozymes in order to assess genetic diversity and structuring of
17 natural populations prospected in the three geographical regions and coinciding with subhumid, humid inferior and semi-arid
superior bioclimates. The analysis of the level and the distribution of the genetic diversity in this species might help in
its conservation. Out of the 18 loci detected for all populations and isozymes analyzed, 12 loci were polymorphic. Allelic
frequencies differed according to populations and particular alleles characterized ecological groups. A high level of genetic
variation within populations was observed. The mean number of alleles per polymorphic locus was Ap = 1.67, the percentage
of polymorphic loci was P = 60.3% and the observed (Ho) and the expected (He) heterozygosities were respectively 0.144 and
0.215. Populations belonging to subhumid (Cap Bon) and semi-arid superior (Tunisian Dorsal) climates, located in degraded
sites exhibited the highest level of inbreeding (0.425 < FIS < 0.450). A high level of differentiation (FST = 0.396) and a low gene flow (Nm = 0.337) among populations, as a result of habitat intermediate destruction, were revealed. The differentiation of populations
within the same bioclimate (or geographic) group was substantial and relatively higher for semi-arid superior populations
(FST = 0.262), which were more distant. The three ecological groups exhibited a high level of structuring (FST = 0.401). These differentiations might be due to geographic distances and to the variations of ecological factors between
sites, including human activities and environmental factors. Nei’s (1972) genetic distances calculated between pairs of populations
were globally low (0.006 < D < 0.367) with a mean of 0.15. They indicate a high level of similarity between populations. UPGMA clustering, established
through Nei’s genetic distances, showed three population aggregates according to their geographic/bioclimatic appartenances.
The high differentiation between populations and the low level of their genetic divergence indicated their recent isolation
under anthropic pressures. The species conservation (in situ or ex situ) strategies should take into account the genetic diversity level within populations and its variation between geographic
groups. |
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Keywords: | Conservation Isolation by distance Isozymes Habitat fragmentation Myrtus communis |
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