Background. Hybridization between native and invasive species can facilitateintrogression of native genes that increase invasive potential by providing exotic specieswith pre-adapted genes suitable for new environments. In this study we assessed theoutcome of hybridization between native Senecio pinnatifolius var. pinnatifolius A.Rich.(dune ecotype) and invasive Senecio madagascariensis Poir. to investigate the potentialfor introgression of adaptive genes to have facilitated S. madagascariensis spread inAustralia.Methods. We used amplified fragment length polymorphisms (141 loci) and nu-clear microsatellites (2 loci) to genotype a total of 118 adults and 223 seeds fromS. pinnatifolius var.pinnatifolius and S. madagascariensis at one allopatric and two sharedsites. We used model based clustering and assignment methods to establish whetherhybrid seed set and mature hybrids occur in the field.Results. We detected no adult hybrids in any population. Low incidence of hybrid seedset was found at Lennox Head where the contact zone overlapped for 20 m (6% and22% of total seeds sampled for S. pinnatifolius var. pinnatifolius and S. madagascariensisrespectively). One hybrid seed was detected at Ballina where a gap of approximately150 m was present between species (2% of total seeds sampled for S. madagascariensis).Conclusions. We found no evidence of adult hybrid plants at two shared sites. Hybridseed set from both species was identified at low levels. Based on these findings weconclude that introgression of adaptive genes from S. pinnatifolius var. pinnatifoliusis unlikely to have facilitated S. madagascariensis invasions in Australia. Revisitationof one site after two years could find no remaining S. pinnatifolius var. pinnatifolius,suggesting that contact zones between these species are dynamic and that S. pinnatifoliusvar. pinnatifolius may be at risk of displacement by S. madagascariensis in coastal areas.
- Biological invasions