Effect of geographical discontinuity on genetic variation in Quercus ilex L. (holm oak). Evidence from enzyme polymorphism

Abstract

Allozymes at a maximum of eight loci were used to analyse the spatial patterns of genetic variation in 1942 hoim oak trees (Quercus ilex L.) from 57 provenances distributed in the six main disjunct areas of the species distribution area. Polymorphism and genetic diversity were high except in the six marginal populations growing in various locations under unfavourable climatic conditions. Ten per cent of the total genetic diversity (H = 0.262) was accounted for by among-population variation. In this long-lived species, the effect of geographical discontinuities on gene flow restriction was shown by the occurrence of: (i) numerous rare alleles limited to a single disjunct region; and (ii) allele frequency variation among the disjunct regions for four alleles. This result was obtained by comparing spatial autocorrelograms from the 57 populations of the entire distribution area and from the 31 populations of the Mediterranean continental region which constitutes the largest continuous area in that distribution. Life history traits (e.g. long life span and high outcrossing rate) and past changes in climate and geographical continuity are assumed to be the main factors responsible for the present genetic variation patterns observed in the species.

Sicily represents the Italian reservoir of chloroplast DNA diversity of Quercus ilex L. (Fagaceae)

“…The analysis of nuclear markers (isozymes) over the whole species distribution revealed that some Sicilian populations were characterised by the occurrence of private alleles [20]. Such evidences underline the need to increase conservation efforts for the preservation of biodiversity in this area, also considering that in Sicily unique tree species like Abies nebrodensis and Zelkova sicula survived as relict.…”

Endemic North African Quercus afares Pomel originates from hybridisation between two genetically very distant oak species (Q. suber L. and Q. canariensis Willd.): evidence from nuclear and cytoplasmic markers

“…Hybrid origin of an oak species Michaud et al (1995), Samuel et al (1995), Toumi and Lumaret (2001) and references therein). In addition, normal allele segregation was observed in intraspecific open pollinated Q. afares progeny.…”

Germination and seedling growth of holm oak (Quercus ilex L.): effects of provenance, temperature, and radicle pruning

“…Quercus ilex (Holm oak), is an evergreen oak species that can be found both in shrub and tree forms (Yaltirik 1984), in pure or mixed stands, and is a typical Mediterranean sclerophyll species (Palacios et al 2009). The holm oak is distributed primarily in three distinct areas: (i) north Africa from Tunisia to Morocco; (ii) on several large islands, e.g., Crete, Sicily, and Corsica; and (iii) in southern (continental) Europe, along a continuum from Turkey to Portugal (Michaud et al 1995). In Turkey, Q. ilex occurs in western Black Sea coasts and in southwestern Anatolia mixed with other pseudomaquis and maquis species, respectively.…”