Occasional hybridization between a native and invasiveSeneciospecies in Australia is unlikely to contribute to invasive success

Abstract

BackgroundHybridization between native and invasive species can facilitate introgression of native genes that increase invasive potential by providing exotic species with pre-adapted genes suitable for new environments. In this study we assessed the outcome of hybridization between nativeSenecio pinnatifoliusvar.pinnatifoliusA.Rich. (dune ecotype) and invasiveSenecio madagascariensisPoir. to investigate the potential for introgression of adaptive genes to have facilitatedS. madagascariensisspread in Australia.MethodsWe used amplified fragment length polymorphisms (141 loci) and nuclear microsatellites (2 loci) to genotype a total of 118 adults and 223 seeds fromS. pinnatifoliusvar.pinnatifoliusandS. madagascariensisat one allopatric and two shared sites. We used model based clustering and assignment methods to establish whether hybrid seed set and mature hybrids occur in the field.ResultsWe detected no adult hybrids in any population. Low incidence of hybrid seed set was found at Lennox Head where the contact zone overlapped for 20 m (6% and 22% of total seeds sampled forS. pinnatifoliusvar.pinnatifoliusandS. madagascariensisrespectively). One hybrid seed was detected at Ballina where a gap of approximately 150 m was present between species (2% of total seeds sampled forS. madagascariensis).ConclusionsWe found no evidence of adult hybrid plants at two shared sites. Hybrid seed set from both species was identified at low levels. Based on these findings we conclude that introgression of adaptive genes fromS. pinnatifoliusvar.pinnatifoliusis unlikely to have facilitatedS. madagascariensisinvasions in Australia. Revisitation of one site after two years could find no remainingS. pinnatifoliusvar. pinnatifolius, suggesting that contact zones between these species are dynamic and thatS. pinnatifoliusvar. pinnatifoliusmay be at risk of displacement byS. madagascariensisin coastal areas.