Chloroplast DNA and nuclear DNA variation in the sympatric alder species, Alnus cordata (Lois.) Duby and A. glutinosa (L.) Gaertn.

Abstract The European alder species, Alnus cordata and A. glutinosa have sympatric distributions on Corsica and southern Italy, where they often grow in mixed populations. An assessment was made of the levels of genetic variation in the chloroplast and nuclear genomes of individual trees from 22 alder populations from Corsica and Italy. The distribution of 10 chloroplast DNA polymorphisms generated by the PCR-RFLP method shows strong geographic structuring of cpDNA haplotypes. Conversely, variation in the nuclear genome, as determined by ISSR analysis, is strongly correlated to the taxonomic affinities of the individual trees analysed. Approximately 50% of ISSR variation ( P =0.00, AMOVA) could be attributed to differences between species. Possible reasons for the incongruence between variation in the chloroplast and nuclear genomes are discussed.