Variations In The Nuclear DNA Content Of The Homoploid Hybrid Species In Senecio

The nuclear content is one of crucial biological characters, closely relating to physiological property, ecological environment and evolutionary history of each species. Homoploid hybridization speciation is one of important, but rare processes in origin of new species. This speciation pattern without a change in ploidy (homoploid hybrid speciation) is well-established in a few plant lineages. A notable example of recent homoploid hybrid speciation is Senecio squalidus (2n=2x=20), which originated in the UK in the 18th Century following introduction of hybrid materials from a hybrid zone between S. chrysanthemifolius (2n=2x=20) and S. aethnensis (2n=2x=20) on Mount Etna, Sicily. To investigate variations of the nuclear DNA contents in this species and between it and parental species, we used the flow cytometry to detect their nuclear DNA contents, using Vigna radiata cv. Berken as internal reference. The results suggested major differences in the nuclear DNA contents between sampled materials. These changes are potentially related to the local adaptation of each species. The nuclear DNA content of S. squalidus is non-additive, however, between those of two parental species. Two possible factors may account for such a DNA content change. First, S. squalidus is a "new" species with a very short history. It is too short for it to produce stable transgressive characteristics, which needs additive effects of the diverse genes. Second, as a successful invasive species, S. squalidus has inherited advantageous genes from parents to occupy new habitats. It is not necessary for it to accumulate additive genes. In addition, we found the northern and southern populations are not differentiated in their DNA contents.