Heterozygote excess in a self-incompatible and partially clonal forest tree species -- Prunus avium L. uri icon

abstract

  • Wild cherry (Prunus avium L.), a partially asexual self-incompatible forest tree, shows heterozygote excess, which is a poorly studied phenomenon. In three natural populations, we found significant heterozygote excess at almost all investigated loci (eight microsatellites and markers for the self-incompatibility locus). We examined four hypotheses to account for this observed heterozygote excess. First, negative F-IS can result from a lack of selfed progeny in small populations of outcrossing species. A second explanation for negative F-IS is selection during the life cycle of the most heterozygous individuals. A third explanation is negative assortative mating when reproduction occurs between individuals bearing phenotypes more dissimilar than by chance. The last explanation for negative F-IS relies on asexual reproduction. Expectations for each hypothesis were tested using empirical data. Patterns of F-IS differed among loci. Nevertheless, our experimental results did not confirm the small sample size hypothesis. Although one locus is probably under a hitch-hiking effect from the SI locus, we rejected the effect of the self-incompatibility locus for the genome as a whole. Similarly, although one locus showed a clear pattern consistent with the selection of heterozygous individuals, the heterosis effect over the whole genome was rejected. Finally, our results revealed that clonality probably explains significant negative F-IS in wild cherry populations when considering all individuals. More theoretical effort is needed to develop expectations and hypotheses, and test them in the case of species combining self-incompatibility and partially asexual reproduction.

publication date

  • 2006
  • 2006