Chloroplast DNA phylogeography of the argan tree of Morocco

Polymorphisms in the chloroplast genome of the argan tree (Sapotaceae), an endemic species of south‐western Morocco, have been detected by restriction site studies of PCR‐amplified fragments. A total of 12 chloroplast DNA (cpDNA) and two mitochondrial DNA (mtDNA) fragments were amplified and digested with a single restriction enzyme (HinfI). Polymorphisms were identified in six of the cpDNA fragments, whereas no mtDNA polymorphisms were detected in a survey of 95 individuals from 19 populations encompassing most of the natural range of the species. The cpDNA polymorphisms allowed the identification of 11 haplotypes. Two lineages, one in the south‐east and the other in the north‐west, divide the range of the argan tree into two distinct areas. The level of genetic differentiation measured at the haplotype level (GSTc= 0.60) (i.e. with unordered haplotypes) was smaller than when phylogenetic relationships were taken into account (NSTc= 0.71‐0.74) (ordered haplotypes), indicating that population history must be considered in the study of the geographical distribution of cpDNA lineages in this species. If contrasted with the level of nuclear genetic differentiation measured in a previous study with isozymes (GSTn= 0.25), the results indicate a relatively high level of gene flow by seeds, or conversely a relatively low level of gene flow by pollen, as compared with other tree species. Goats and camels could have played an important role in disseminating the fruits of this tree.

[1]  C. Birky.  Uniparental inheritance of mitochondrial and chloroplast genes: mechanisms and evolution. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[2]  F. Sorensen,et al.  Mitochondrial DNA products among RAPD profiles are frequent and strongly differentiated between races of Douglas‐fir , 1995, Molecular ecology.

[3]  R. Petit,et al.  A set of universal primers for amplification of polymorphic non‐coding regions of mitochondrial and chloroplast DNA in plants , 1995, Molecular ecology.

[4]  P. Taberlet,et al.  The use of chloroplast DNA to resolve plant phylogenies: noncoding versus rbcL sequences. , 1994, Molecular biology and evolution.

[5]  M. Byrne,et al.  Population divergence in the chloroplast genome of Eucalyptus nitens , 1994, Heredity.

[6]  R. Ennos.  Estimating the relative rates of pollen and seed migration among plant populations , 1994, Heredity.

[7]  R. Petit,et al.  Finite island model for organelle and nuclear genes in plants , 1993, Heredity.

[8]  J. Bousquet,et al.  The rbcL gene sequence from chestnut indicates a slow rate of evolution in the Fagaceae. , 1993, Genome.

[9]  L. Excoffier,et al.  Analysis of molecular variance inferred from metric distances among DNA haplotypes: application to human mitochondrial DNA restriction data. , 1992, Genetics.

[10]  D. Soltis,et al.  Chloroplast-DNA variation in Tellima grandiflora (Saxifragaceae) , 1991 .

[11]  J. Letouzey,et al.  Allozymic variability in beechwoods (Fagus sylvatica L.) over central Europe: spatial differentiation among and within populations , 1990, Heredity.

[12]  M. Lynch,et al.  The analysis of population survey data on DNA sequence variation. , 1990, Molecular biology and evolution.

[13]  P. Li,et al.  Range-wide patterns of allozyme variation in Douglas-fir (Pseudotsugamenziesii) , 1989 .

[14]  Wen-Hsiung Li,et al.  Rates of nucleotide substitution vary greatly among plant mitochondrial, chloroplast, and nuclear DNAs. , 1987, Proceedings of the National Academy of Sciences of the United States of America.

[15]  M. Clegg,et al.  The Nature of Nucleotide Sequence Divergence between Barley and Maize Chloroplast DNA. , 1984, Genetics.

[16]  N. Wheeler,et al.  Population structure, genic diversity, and morphological variation in Pinuscontorta Dougl. , 1982 .

[17]  K. Holsinger,et al.  Chloroplast DNA Haplotype Variation within and among Populations of Coreopsis grandiflora (Asteraceae) , 1995 .

[18]  E. Routman,et al.  Separating population structure from population history: a cladistic analysis of the geographical distribution of mitochondrial DNA haplotypes in the tiger salamander, Ambystoma tigrinum. , 1995, Genetics.

[19]  L. Excoffier,et al.  Using allele frequencies and geographic subdivision to reconstruct gene trees within a species: molecular variance parsimony. , 1994, Genetics.

[20]  P. Taberlet,et al.  Chloroplast Dna Polymorphism At The Intrageneric Level And Plant Phylogenies , 1994 .

[21]  R. Petit.  Polymorphisme de l'adn chloroplastique dans un complexe d'especes : les chenes blancs europeens. subdivision de la diversite des genes cytoplasmiques chez les plantes , 1992 .