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

BACKGROUND

Hybridization 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 native var. A.Rich. (dune ecotype) and invasive Poir. to investigate the potential for introgression of adaptive genes to have facilitated spread in Australia.

METHODS

We used amplified fragment length polymorphisms (141 loci) and nuclear microsatellites (2 loci) to genotype a total of 118 adults and 223 seeds from var. and at 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.

RESULTS

We 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 for var. and respectively). One hybrid seed was detected at Ballina where a gap of approximately 150 m was present between species (2% of total seeds sampled for ).

CONCLUSIONS

We 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 from var. is unlikely to have facilitated invasions in Australia. Revisitation of one site after two years could find no remaining var. , suggesting that contact zones between these species are dynamic and that var.  may be at risk of displacement by in coastal areas.